The journal of raptor research - Internet...

The Journal of

Raptor ResearchVolume 36 Number 4 December 2002

Published by

The Raptor Research Foundation* Inc

THE RAPTOR RESEARCH FOUNDATION, INC.

(Founded 1966)

OFFICERS

PRESIDENT: Brian A. Miu sap SECRETARY: Judith HenckelVICE-PRESIDENT: Keith L. Bildstein TREASURER: Jim Fitzpatrick

BOARD OF DIRECTORS

NORTH AMERICAN DIRECTOR #1:

Philip Detrich

NORTH AMERICAN DIRECTOR #2;

Iaurie J. Goodrich

NORTH AMERICAN DIRECTOR #3:

Jeff P. Smith

INTERNATIONAL DIRECTOR #1:

Eduardo Inigo-Elias


Ricardo Rodriquez-Estrella


Beatriz Arroyo

DIRECTOR AT LARGE #1: Jemima ParryJones

DIRECTOR AT LARGE #2: Petra Bohall WoodDIRECTOR AT LARGE #3: Michael W. Collopy

DIRECTOR AT LARGE #4: Carol McIntyre

DIRECTOR AT LARGE #5: Robert N. Rosenfield

DIRECTOR AT LARGE #6; Ed Henckel

EDITORIAL STAFF

EDITOR: James C. Bednarz, Department of Biological Sciences, P.O. Box 599, Arkansas State

University, State University, AR 72467 U.S.A.

ASSOCIATE EDITORS

James R. BeithoffClint W. Boai.

Joan L. MorrisonJuan Jose Negro

Marco Resiani

Ian G. WarkentinTroy I. Wellicome

BOOK REVIEW EDITOR: Jeffreys. Marks, Montana Cooperative Research Unit, University of Montana,Missoula, MT 59812 U.S.A.

SPANISH EDITOR: Cesar Marquez Reyes, Instituto Humboldt, Colombia, AA. 094766, Bogota 8, ColombiaEDITORIAL ASSISTANTS: Rebecca S. Maul, Kristina Baker, Joan Clark

The Journal of Raptor Research is distributed quarterly to all current members. Original manuscripts

dealing with the biology and conservation of diurnal and nocturnal birds of prey are welcomed fromthroughout the world, but must be written in English. Submissions can be in the form of research articles,

short communications, letters to the editor, and book reviews. Contributors should submit a typewritten

original and three copies to the Editor. All submissions must be typewritten and double-spaced on oneside of 216 X 278 mm (8% X 11 in.) or standard international, white, bond paper, with 25 mm (1 in.) mar-

gins. The cover page should contain a title, the author’s full name(s) and address (es). Name and address

should be centered on the cover page. If the current address is different, indicate this via a footnote. Ashort version of the title, not exceeding 35 characters, should be provided for a running head. Anabstract of about 250 words should accompany all research articles on a separate page.

Tables, one to a page, should be double-spaced throughout and be assigned consecutive Arabic numer-als. Collect all figure legends on a separate page. Each illustration should be centered on a single pageand be no smaller than final size and no larger than twice final size. The name of the author (s) and figure

number, assigned consecutively using Arabic numerals, should be pencilled on the back of each figure.

Names for birds should follow the A.O.U. Checklist of North American Birds (7th ed., 1998) or another

authoritative source for other regions. Subspecific identification should be cited only when pertinent to

the material presented. Metric units should be used for all measurements. Use the 24-hour clock (e.g.,

0830 H and 2030 H) and “continental” dating (e.g., 1 January 1999).

Refer to a recent issue of the journal for details in format. Explicit instructions and publication policy

are outlined in “Information for contributors , Raptor Res., Vol. 36(4), and are available from the editor.

Submit manuscripts to J. Bednarz at the address listed above.

COVER: Bald Eagles {Haliaeetus leucocephalus)

.

Painting byJohn Schmitt.

ContentsForaging Ecology of Nesting Bald Eagles in Arizona, w. Grainger Hunt, Ronald e.

Jackman, Daniel E. Driscoll, and Edward W. Bianchi 245

Vernal Migration of Bald Eagles from a Southern Colorado Wintering Area.

Alan R. Harmata 256

Does Northern Goshawk Breeding Occupancy Vary with Nest-stand Character-

istics ON THE Olympic Peninsula, Washington? Sean p. Finn, Daniel e. Variand, and

John M. Marzluff 265

Subordinate Males Sire Offspring in Madagascar Fish-Eagle {Hauaeetus vocife-

ROIDES) PoLYANDROUS BREEDING GROUPS. Ruth E. Tingay, Melanie Culver, Eric M.

Hallerman, James D. Fraser, and Richard T. Watson 280

Nesting and Perching Habitat Use of the Madagascar Fish-Eagle. James Berkeiman,

James D. Fraser, and Richard T Watson 287

Use of Vegetative Structure by Powerful Owls in Outer Urban Melbourne,

Victoria, Australia—Implications for Management. Rayiene Cooke, Robert Waiiis,

andJohn White 294

Nest-site Selection of the Crowned Hawk-Eagle in the Forests of Kwazulu-

NATAL, South Africa, and TaI, Ivory Coast. Gerard Malan and Susanne Shultz 300

Short Communications

Juvenile Dispersal of Madagascar Fish-Eagles Tracked by Satellite Telemetry. Simon

Rafanomezantsoa, Richard T. Watson, and Russell Thorstrom 309

Prey of the Peregrine Falcon (Falco Peregiunus cassini) in Southern Argentina and Chile. David

H. Ellis, Beth Ann Sabo, James K. Tackier, and Brian A. Millsap 315

An Elevated Net Assembly to Capture Nesting Raptors. Eugene A. Jacobs and Glenn A. Proudfoot 320

Florida Bald Eagle {Hauaeetus leucocephalus) Egg Characteristics. M. Alan Jenkins, Steve KSherrod, David A. Wiedenfeld, and Donald H. Wolfe, Jr. 324

Osprey Ecology in the Mangroves of Southeastern Brazil. Robson Silva e Silva and Fabio Olmos 328

Diet of Breeding Tropical Screech-Owls (Otus chouba) in Southeastern Brazil. Jose Carlos

Mottajunior 332

Letters

Comments of the First Nesting Record of the Nest of a Slaty-backed Forest Falcon {Micrastur

MIRANDOUEJ) IN THE ECUADORIAN AMAZON. Russell Thorstrom 335

Micrastur or Acupiter, That is the Question. Tjitte de Vries and Cristian Melo 337

Book Reviews. Edited byJeffery S. Marks 338

Information For Contributors 340

Index to Volume 36 344

The Raptor Research Foundation, Inc. gratefully acknowledges funds and logistical supportprovided by Arkansas State University to assist in the publication of the journal.

THE JOURNAL OF RAPTOR RESEARCHA QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.

VoL. 36 December 2002 No. 4

/. Raptor Res. 36(4):245-255

© 2002 The Raptor Research Foundation, Inc.

FORAGING ECOLOGY OF NESTING BALD EAGLES IN ARIZONA

W. Grainger Hunt/ Ronald E. Jackman, and Daniel E. DriscollPredatory Bird Research Group, Long Marine Laboratory,

University of California, Santa Cruz, CA 93060 U.S.A.

Edward W. BianchiEntrix, 7919 Folsom Blvd., Suite 100, Sacramento, CA 93826 U.S.A.

Abstract.—^We studied foraging ecology of nesting Bald Eagles (Haliaeetus leucocephalus) in Arizona

during 1987-89, with emphasis on the influence of dams and river flow regulation. We examined diet,

foraging modes, habitat selection, fish abundance, and factors associated with fish availability. Based onbiomass, prey remains yielded 76% fish, 14% mammals, and 10% birds. On rivers, eagles primarily

caught live fish as they spawned or foraged in shallow water, whereas, on reservoirs, most fish were

obtained as carrion or as they floated moribund on the surface. Fish communities differed among river

reaches and reservoirs, and ecological and life-history characteristics influenced vulnerability and sea-

sonal differences in exploitation, Water temperature, a principal factor determining fish communitystructure among eagle territories, was also associated with temporal differences in fish availability, as was

flow and turbidity. Few prey sources remained constant throughout the reproductive cycle, and prey

and habitat diversity buffered temporal changes in prey availability. We conclude that dams benefit

breeding eagles to the extent that they create water temperature discontinuities and additional aquatic

habitats, some that support large populations of fish. However, environments modified by dams are not

necessarily better for Bald Eagles than those on free-flowing sections of rivers; our data show that Bald

Eagle reproduction in the two settings is nearly identical.

Key Words: Bald Eagle, Haliaeetus leucocephalus; dams; habitat selection; home range, piscivory; radiotelem-

etry; rivers.

ECOLOGIA DEL FORRAJEO DE AGUILAS CALVAS NIDIFICANDO EN ARIZONA

Resumen.—Estudiamos la ecologia de forrajeo de aguilas calvas {Haliaeetus leucocephalus) nidificando enArizona durante 1987-89, con enfasis en la influencia de los embalses y la regulacion del flujo de los

rios. Examinamos la dieta, modos de forrajeo, seleccion de habitat, abundancia de peces, y factores

asociados con la disponibilidad de peces. Tomando como base la biomasa, los restos de presas arrojaron

76% peces, 14% mamiferos, y 10% aves. En los rios, las aguilas ante todo capturaron peces vivos cuandoestos desovaban o forrajeaban en aguas someras, mientras que, en los reservorios, la mayoria del pescado

fue obtenido como carrona o cuando flotaban moribundos sobre la superficie. Las comunidades de

peces difirieron entre los limites de los rios y las caracteristicas ecologicas y de su historia de vida las

cuales influyeron en la vulnerabilidad y las diferencias estacionales en la explotacion. La temperatura

del agua, un factor primordial determinante de la estructura de la comunidad ictica entre los territorios

de las aguilas, fue asociada ademas con las diferencias temporales en disponibilidad de peces, tal comolo fue con el flujo y la turbidez. Pocos recursos de presas permanecieron constantes a traves de todo el

ciclo reproductivo, y las presas y diversidad de habitats amortiguaron los cambios temporales en la

disponibilidad de presas. Concluimos que los embalses benefician las aguilas que estan reproduciendose

en el sentido en que crean discontinuidades en la temperatura y habitats acuaticos adicionales, algunos

^ Present address: The Peregrine Fund, 5568 West Flying Hawk Lane, Boise, ID 83709 U.S.A.; e-mail address:

[email protected]

245

246 Hunt et al. VoL. 36, No. 4

de los cuales soportan grandes poblaciones de peces. Sin embargo, los ambientes modificados por las

represas no son necesariaraente mejores para las aguilas pescadoras que aquellos que estan en secciones

de libre flujo en los rios; nuestros datos muestran que la reproduccion de las aguilas pescadores en los

dos escenarios son cercanamente identicos.

[Traduccion de Cesar Marquez]

Population persistence in raptors and other ter-

ritorial birds depends on an aggregate of breeding

locations that contribute to above-replacement-rate

reproduction (Hunt and Law 2000). Conserving

high-quality sites requires knowledge of key com-

ponents, some being physiographic, others de-

pending on the ecology, behavior, and life-history

characteristics of associated biota. Of particular in-

terest are factors relating to food acquisition. Re-

productive success requires that breeding pairs

have sustained access to prey within efficient com-

muting distance (Royama 1970). For species with

prolonged breeding cycles (ca. 5 mo for North

American eagles), during which numerous phe-

nological events transpire, food continuity may in-

volve switching from one prey type to another over

the course of the nesting season (Jamieson et al.

1982, Edwards 1988).

Prey remains collected from nests of inland-

breeding Bald Eagles {Haliaeetus leucocephalus) of-

ten show dietary diversity. This has been observed

not only for populations as a whole, but for indi-

vidual nests (Todd et al. 1982,Jackman et al. 1999).

Thus, it is tempting to hypothesize that prey variety

and, by inference, environmental variation within

the foraging range are important components of

Bald Eagle territories in some regions (Grubb

1995).

From January 1987-June 1989, we investigated

the effects of dams and flow regulation on the nest-

ing population of Bald Eagles in central Arizona

(Driscoll et al. 1999). We obtained information onthe spatial and temporal aspects of foraging. Werecorded shifts of eagle prey use, foraging behav-

ior, and ranging patterns that followed temporal

variation in factors influencing prey availability. Wefound that water temperature and clarity, the struc-

ture of various riverine and lacustrine habitats, and

life-histories and behavior of prey species were in-

terrelated with respect to food availability.

Study Area

General Description. Our study centered on Bald Ea-

gle breeding territories along the Salt and Verde rivers

in central Arizona (Fig. 1), a generally open, desert land-

scape of the Upper and Lower Sonoran Life-Zones (Lowe

1964, Brown 1998). Eagles nested at elevations ranging

from ,329-1719 mask Riparian environments in these re-

gions are composed of Sonoran Riparian Deciduous For-

est and Woodlands Biome, Sonoran Riparian Scrubland

Biome, and the Sonoran Interior Strands Biome. Up-lands in the Lower Sonoran Life Zone are all within Son-

oran Desertscrub Biome (Brown 1998). Upper SonoranLife Zone (Brown 1998) vegetative composition near

Bald Eagle breeding territories includes Great Basin Co-

nifer Woodland, Interior Chaparral, and Semidesert

Grassland Biomes. Mean annual precipitation ranges

from 39 cm at higher elevations to 25 cm in the low

desert where temperatures may reach 50°C.

The central Arizona landscape has been greatly altered

by human activity. Cattle grazing, particularly after railway

development in the late 1800s, resulted in dramatic ero-

sion (Hastings 1959, Hastings and Turner 1965, Hayden1965). This and woodcutting reduced riparian forests to

a scattering of isolated groves and trees. Soil loss drained

near-surface aquifers, creating drier soil conditions, andlivers became muddy torrents following rains. With the

increased need for flood control, water storage, and ir-

rigation, hve impoundments were constructed on the

Salt River and two on the Verde River during the early

1900s. Riverine environments downstream of the reser-

voirs were changed by flow regulation and sediment fil-

tration, and upstream by migrations of fish populations

such as common carp {Cyprinus carpio) and catfish (Ic-

taluridae) out of the reservoirs.

Fisheries. Three native species of fish, appropriate for

eagle exploitation, remain in substantial numbers within

the study area: desert sucker {Catostomus insignis), Sonora

sucker (C. clarki), and roundtail chub {Gila robusta)

(Minckley 1973). Introduced species of potential impor-

tance to eagles in rivers and/or reservoirs include chan-

nel catfish {Ictalurus punctaLus), bullhead {Ameiurus ne-

bulosus and A. natalis), flathead catfish {Pylodictis olivaris)

,

common carp, black crappie {Pomoxis nigromaculatus)

,

yellow bass (Morone mississippiensis)

,

largemouth bass {Mi-

cropterus salmoides), smallniouth bass {M. dolomieui), blue-

gill {Lepomis macwchirus)

,

green sunfish {L. cyanellus),

and walleye (Stizostedion vitreum).

Fish distribution in central Arizona, as elsewhere, is

strongly influenced by water temperature (Vannote et al

1980, this study). Trout (Salmonidae) inhabit cool head-

waters. Suckers, smallmouth hass, and then channel cat-

fish increase in abundance as water warms downstreamWith increasing water temperature, carp and catfish be-

come the primary species in size categories suitable for

Bald Eagle foraging. When a river enters a reservoir, per-

ciforms (hass, perch, and crappie) predominate, al-

though carp and catfish cemtribute importantly to overall

fish biomass in the reservoir. Water temperature and vol-

ume released from the reservoir influence the fish com-munity below the dam. Cool releases from the hypolim-

nion of deep, stratified reservoirs favor sucker

populations. If the reservoir is shallow or unstable and

December 2002 Bald Eagle Foraging Ecology 247

Figure 1. The Salt and Verde river systems of central Arizona. The six names in italics identify breeding territories

where Bald Eagle foraging was studied with radio telemetry.

fails to maintain a cool hypolimnion, or if releases issue

from the epilimnion, warm releases favor carp and catfish

in the river reach below the dam. During spring, spawn-

ing runs of carp and catfish from downstream reservoirs

may augment riverine fish populations.

Study Sites. We studied Bald Eagle foraging at six

breeding territories (defined here to include the forag-

ing range) chosen to compare regulated with unregulat-

ed (i.e., free-flowing) environments (Fig. 1). All six ter-

ritories have been occupied by eagles since the 1970s

(Driscoll et al. 1999). Two breeding territories (Ladders

and East Verde) were on free-flowing rivers far from res-

ervoirs. Two other pairs (Bardett and Blue Point) occu-

pied settings in which all flows were regulated by damreleases, i.e., reservoirs releasing cold water and fed by

other dams upstream. The remaining two breeding ter-

ritories (Horseshoe and Pinal) included both reservoir

systems and the free-flowing rivers that fed them.

Methods

Telemetry. We used radio-controlled bow nets, powersnares, and noosed fish (Jackman et al. 1993, 1994) to

capture territorial eagles for radio-tagging. We attached

65-g transmitters with a backpack configuration of teflon

ribbons adjoined with cotton string over the carina to

permit eventual loss of the radio (Hunt et al. 1992,

McClelland et al. 1994). Mercury (activity) switches

changed the pulse rate when tilted from near-vertical to

horizontal (Kenward 2001). We refined signal interpre-

tation on the basis of frequent visual verification.

From the early brooding period to fledging, tracking

teams collected data in 8-d sessions separated by 6-d pe-

riods of no data collection. The objective was to obtain

uninterrupted, minute-by-minute records (time lines) of

movements and activities of radio-tagged eagles. To over-

come the bias associated with observer location, trackers

spread out to strategic viewing sites and maintained com-


munication by hand-held radios. Tracking teams of three

to five members later conferred to eliminate duplicate

data points. To reference eagle locations, habitat vari-

ables, and prey, we marked river centerlines and reservoir

shorelines depicted on USGS topographic maps to show1-km and 0.1-km intervals. If we could not identify the

eagle’s location to the level of even a 1-km segment, wemarked the location within larger zones positioned be-

tween familiar landmarks.

We measured variables at prey-strike points as soon as

possible after a foraging event but without disturbing the

eagle. Recorded information included attack methodand aquatic habitat type, as follows: “pools” are depres-

sions in the streambed, with hydrologic control in the

downstream end and low current velocities relative to

prevailing streamflow; “runs” are moderately deep, usu-

ally narrow channels with relatively fast current, but little

or no white water; “riffles” are characterized by shallow,

fast-moving water flowing down gradients and over sub-

strates usually no larger than small boulders; “pocket wa-

ter” usually contains larger boulders, with fast water in-

terspersed across the width of the stream among frequent

pockets of quiet water; “cascades” are steep gradient

white water with less than 10% quiet water (Hunt et al.

1992). Microhabitat features measured at strike points in-

cluded water depth, water temperature, and turbidity

(Secchi disk). We collected evidence (e.g., scales) of prey

species identity, and estimated prey size and whether it

was obtained alive or as carrion.

Prey Delivery, Observers recorded prey deliveries to

the nests from points permitting clear views of nest bowls

and at distances of 125-400 m, typically beginning whenyoung were 2-3 wk of age. Prey items were assigned to

general taxonomic categories (e.g., class), then to morespecific categories (e.g., family, species), where possible.

For fish, diagnostic features included fin and scale char-

acteristics, body and mouth shapes, jaw configurations,

barbel presence, caudal peduncle thickness, and mark-

ings. Observers noted their confidence in each identifi-

cation; items identified with low confidence were as-

signed to a higher taxonomic level. We sometimes

confirmed identification with body parts (e.g., scales) col-

lected at eagle foraging sites. We did not distinguish be-

tween desert and Sonora suckers. We estimated prey size

by comparing the item with the length of the eagle’s bill

or with objects of known size in the nest.

Analysis of Tracking Data. Time line tracking data con-

sisted of 22 742 records of the movements and activities

ol nine radio-tagged adults in six breeding territories, for

a mean of 2327 records per tagged eagle. We recorded

the number of minutes an eagle remained at a location

and the frequency of visits to each location. The first

mea.sure (time) offered a relatively poor estimate of area

use compared to relocation frequency. Consider an ex-

ample in which an eagle loafed for 146 min at a location

300 m downstream of the nest (in sight of the nest), then

flew 2 km upstream where it perched for 5 min at each

of three locations, some 200 m apart. At the last of these,

the eagle caught a fish, after which it returned to the

nest area where it spent 62 rain. Clearly, a time-based

assessment awards small significance to the foraging area

where the eagle spent only 2% of its time. By contrast,

the relocation-based appraisal recognized each of the 0.1-

km segments (or larger zones) where the eagle perched.

Weighting each location equally as a measure of use was

supported by our data: in 80% of observed foraging

events, the eagle perched within sight of the foraging

location just before the event, and in 70% of cases, the

eagle appeared to have seen the prey before leaving the

perch.

Each perching visit to a O.Tkm segment received a

score of one point. If the eagle left a location and en-

tered another O.l-km segment along the river, but then

returned to the original location, the latter received an-

other point. Segments visited repeatedly thereby received

the most points. The large number of nest visits over-

shadowed other relocation scores; however, eliminating

the nest area from the analysis was inappropriate because

the nest vicinity was often an important foraging area.

Therefore, we used the prey delivery data to estimate the

percentage of foraging events occurring in the nest vicin-

ity. This became the relocation percentage for the nest

area, and percentages for all other areas within the homerange were adjusted accordingly so the total was 100%.

Collection and Analysis of Prey Remains. Collection. Wecollected prey remains within and below nests at five of

the six breeding territories studied (one nest was on an

inaccessible pinnacle) and at 16 other breeding sites in

Arizona. Collections occurred during the middle to late

part of the brood-rearing period and again after the

young had fledged. We attributed variation in the

amount of remains present to removal by the adults (ob-

served) and to the activities of woodrats (Neotoma spp.)

and other scavengers. We collected ca. 2 L of fine nest

lining from each nest for scale analysis to detect soft-

boned fish (e.g., trout, chub) (Jackman et al. 1999).

Analysis. We collected 5—10 individuals of differing sizes

of each fish species expected to occur in the eagles’ diet.

We weighed and measured each fish, then parboiled it

to remove all flesh. We weighed, dried, and labeled all

bones for reference.

We developed regression equations to relate bonelength to total body length for each species (Hunt et al.

1992, Jackman et al. 1999). Because unattached bones

were often from the same fish, we used the following

procedure to avoid duplication: first, we determined the

95% confidence intervals from each equation to deter-

mine the probable range of total length represented by

the bones. For a given collection and species, we calcu-

lated fish total length from each bone and then sorted

all like bones. Bones with the most entries and relatively

low confidence intervals were examined first. Wegrouped pairs of these bones of the same size (<1.0 mmdifference or <5 mm for broken bones), e.g., left andright opercula. We marked each pair and the remaining

odd entries as individual prey items. We next matchedthe opcrcula(s) from one fish with other bones whoseconfidence intervals for total body lengths overlapped

with those computed from the opercula. Because differ-

ent parts of the same fish had specific proportional re-

lationships (e.g,, ±2.0 mm for sucker opercula and clav-

icles), we eliminated those entries that were eclipsed by

the confidence intervals, a procedure that left the fewest

numbers of unmatched parts and, thus, the fewest pos-

sible number of individual fish represented. Results un-

December 2002 Baed Eagi.e Foraging Ecology 249

derestimated total fish numbers to the extent that

matched parts may have been from different fish.

We calculated total mass for the selected (nondupli-

cate) fish prey items, using length-to-mass equations fromthis study and from Carlander (1969, 1977) and Becker

(1983). We subtracted the mass of bones and scales

(from regression equations) plus 5% of total mass (esti-

mated unavailable biomass) to calculate the edible bio-

mass for each prey item. We identified nonfish remains

from museum reference collections and then used stan-

dard body mass for each species less 10% for inedible

parts.

Fish Sampling. Objectives of fish sampling within eagle

territories were to identify: (1) relative abundance ofprey

fish, (2) seasonal changes in their distribution, with em-phasis on availability to eagles (e.g., fish moving into shal-

low water), (3) spawning and its effect on fish availability,

and (4) effects of water management on prey fish avail-

ability.

Fish abundance, activity, and distribution. We conducted

both roving and fixed-point visual surveys. In roving sur-

veys, one or two biologists (depending upon flow) walked

along the river bank, noting abundance and activity of

fish, aquatic habitat, depth, location (within standard 0.1-

km segment), and water temperature. We also observed

fish activity and behavior from fixed points. Prior to sur-

veying, we compiled information on fish communities in

the various river reaches, tributaries, and reservoirs, in-

cluding Arizona Game and Fish Department (AGFD)and U.S. Fish and Wildlife Service reports and field data

from D. Henrickson (AGFD), M. Jakle (U.S. Bureau of

Reclamation), and C. Zeibell (Arizona Cooperative Fish-

eries Unit)

.

To verify our observational data and to determine go-

nadal development, we sampled fish in representative

habitats with gill nets and throw nets, and occasionally by

snorkeling surveys. We removed all collected fish fromthe system, many of which were used in the prey refer-

ence series. We conducted an electrofishing survey at the

East Verde territory just after the eagle nesting season.

Aquatic habitat surveys. We surveyed aquatic habitat dis-

tribution in four of the six eagle territories. We mappedsections of rivers and tributaries within eagle home rang-

es into basic habitat units, including pools, runs, riffles,

pocket water, and cascades, as defined by Hunt et al.

(1992). We differentiated between two types of riffles:

channel-riffles, which become runs during moderate flow

increase, and bar-riffles which remain as riffles under a

variety of flows. Bar-riffles are characterized by the pres-

ence of a gravel/cobble bar oriented diagonally or per-

pendicularly to flow. As flow increases, water depth andvelocity increase only partially in bar-riffles, whereas the

amount of shallow water increases overall due to spread-

ing of water across the gravel/cobble bar. We mappedreservoirs according to distributions of shallow water ar-

eas. We obtained river flow and reservoir water surface

elevation data from agencies maintaining gaging stations.

Carrion and Waterbird Surveys. We conducted peri-

odic surveys on rivers and reservoirs to assess temporal

availability of carrion. We sampled representative stretch-

es of reservoir shoreline where we expected carrion to

accumulate, e.g., coves, bends, and especially where riv-

ers entered reservoirs. We slowly followed shorelines by

boat, identifying and measuring all carrion fish, birds,

and mammals encountered. We noted factors contribut-

ing to death, e.g., trauma, evidence of spawning, fishing

paraphernalia. On rivers, we selected one to three 100-

m areas in each territory where carrion was likely to ac-

cumulate, and with particular attention to channelbends. We surveyed for waterbirds from one or two

points offering wide views per territory, or by makingcounts while traveling along water bodies (e.g., during

carrion surveys), noting the species and numbers pres-

ent.

Results

Diet. We identified 19 species of fish, 26 birds,

16 mammals, and three reptiles from (1) the re-

mains of 2601 prey individuals collected from

nests, under perches, and after foraging events at

23 breeding territories, and (2) observations of

713 prey items delivered to nests (Table 1). Meanbiomass percentages for each class in remains from

all sites were 75.5% fish, 14.3% mammals, and

10.2% birds. Four groups accounted for nearly all

fish biomass: catfish (mainly channel catfish), suck-

er (desert and Sonora suckers), carp, and perci-

forms (mainly largemouth bass, black crappie, and

yellow bass). Seven taxa exceeded 15% of fish bio-

mass at one or more of 23 territories sampled in

central Arizona: sucker at 12 territories, carp at 12,

channel catfish at 10, largemouth bass at six, flat-

head catfish at three, crappie at two, and yellow

bass at two.

Comparisons of prey remains with prey deliver-

ies over similar time frames consistently showed

that biomass estimates from remains overrepre-

sented mammals and birds over fish, and catfish

over suckers and perciforms (Hunt et al. 1992). In

three territories where items and deliveries were

within comparable time frames, 7 of 56 fish

(10.3%) identified in remains were suckers, where-

as 124 of 342 (33.2%) fish deliveries were suckers

(X^ = 13.1, df — 1,7* = 0.0003). Remains versus

delivery ratios for catfish in these samples were 24:

56 (42.8%) and 56:342 (16.4%) (x^ = 47.6, df =

1, P < 0.0001). An experiment involving a blind

sample of 45 fish fed to a captive eagle supported

our field data in that soft-boned fishes tended to

be underrepresented, e.g., 100% of carp appeared

in the remains, 80% of catfish, 60% of the some-

what softer-boned suckers, and only 8% of trout (T.

Gatz and M. Jakle, unpubl. data).

As expected, suckers were the most commonprey for pairs nesting on cool, free-flowing reaches

nearest the headwaters or at sites offering access

to regulated river reaches downstream of hypolim-


Table 1. Prey biomass estimates from prey remains and observed prey deliveries (in italics) for fl Bald Eagle

territories on the Salt and Verde rivers where sample sizes exceeded 40 items. Letters in parentheses refer to damreleases from the cool hypolimnion (C) or the warm epilimnion (W).

Percent Biomass

Breeding

Area Setting N Suckers Carp Catfish

Perci-

forms

Mam-mals Birds Other

Ladders Free-flowing river 79 8 48 20 1 18 5 0

deliveries 130 45 33 17 0 3 0 2

East Verde 95 5 47 27 2 12 5 2

deliveries 103 14 49 17 8 6 0 6

Redmond 156 5 18 55 1 12 4 5

Final Free-flowing river 107 5 19 47 13 8 8 0

deliveries and reservoir 46 0 10 55 27 0 3 5

Horseshoe 95 1 8 36 31 4 19 1

deliveries 48 0 34 11 40 2 0 13

Blue Point Regulated river (C) 85 10 7 21 22 18 22 0

deliveries and reservoir 152 28 2 9 41 8 8 4

Bartlett 47 55 11 18 7 9 0 0

deliveries 234 66 2 9 15 6 0 2

Orme Regulated river 56 45 4 3 2 34 12 0

Et. McDowell 62 66 5 5 1 18 5 0

Chff Regulated river (W)

and reservoir

45 0 46 18 27 5 4 0

“76” Creek 59 5 38 2 1 41 13 0

netic dam releases (Table 1). Perciforms were tak-

en mainly in the reservoirs. Eagles obtained carp

primarily in warm, free-flowing reaches upstream

of reservoirs and in a river fed by epilimnetic re-

leases (Table 1). Catfish (channel and flathead)

were widely utilized, the highest numbers taken

from free-flowing river reaches and in a reservoir

(Alamo) with only seasonal inflow (Haywood andOhmart 1986).

Estimates of mammal biomass from remains ex-

ceeded 25% at six breeding territories. Most fre-

quently identified were black-tailed jackrabbit {Le-

pus californicus) and cottontail rabbit (Sylvilagus

audubonii). We recorded only 32 mammals among713 prey items observed delivered to nests (4.5%

of items) despite a more substantial representation

m prey remains from those nests (18.3%). We at-

tribute this disparity to the greater use of mammalsearly in the breeding season and to biases associ-

ated with bone persistence.

Waterbirds were more important to Bald Eagles

in early winter than during the nesting season, par-

ticularly at territories containing reservoirs. In win-

ter, the percentages of birds observed taken (as

compared with fish) were 50% in December, 56%in January, and 13% in February, as compared with

5% in March, 1% in April, and 0% in May. The most

commonly recorded birds taken among 30 identi-

fied were American Coots {Fulica americana, N— 15)

and Eared Grebes {Podiceps nigricollis, N = 8).

Conditions of Prey Acquisition. Eagles took

some fish species only in riverine conditions, oth-

ers only from reservoirs, and some from both. Ofthe seven important fish taxa recorded during prey

delivery observation, numerical ratios of their ori-

gin in rivers versus reservoirs at four territories

containing both environments were as follows (riv-

er : reservoir):yellow bass (0:31), crappie spp. (0;

40), largemouth bass (2:22), flathead catfish (3:5),

channel catfish (4:17), sucker spp. (105:0), and

carp (3:30). In reservoirs, eagles obtained most fish

as carrion (or moribund), i.e., 66% of 125 fish of

known status (excluding piracies) were obtained

from reservoirs as carrion, whereas 12% of 201 fish

from rivers were carrion.

Suckers. At least 83% {N = 114) of suckers were

alive when taken, 5% were pirated, 3% were car-

rion, and 9% were of unknown status. Bald Eagles


caught them mainly in riffles while they spawned

or foraged. Of 64 depth measurements at strike

points for live suckers, 80% were in water <30 cmin depth; mean depth at strike points of these 51

shallow water captures was 16.4 cm (SD ± 7.3).

Carp. Eagles obtained carp from both rivers and

reservoirs. In rivers, eagles caught them in the shal-

lows of runs and riffles, 17 of 20 strikes in water

less than 36 cm deep. We were unable to deter-

mine under what conditions carp were captured in

reservoirs.

Catfish. We estimate from prey collections that

channel catfish contributed almost three times the

biomass as flathead catfish (301 182 g versus 92 304

g, respectively). Excluding piracies, we observed

nesting Bald Eagles taking channel catfish on 51

occasions: 75% on reservoirs and 25% on rivers.

On reservoirs, 81% of 26 catfish of known status

were obtained as carrion, whereas on rivers, 27%of 11 were carrion. Although the sample of con-

ditions at strike points for live channel catfish in

rivers was small, it differed from those noted for

other species. Eagles captured five in pocket water,

three in runs, and none from riffles. The mean of

six depth measurements was 58 cm (SD ± 28.1).

We occasionally observed catfish swimming near

the surface in riverine pools (Van Daele and Van

Daele 1982), and “blooms” of carrion channel cat-

fish (ca. 20 cm long) appeared in late spring at two

reservoirs (Horseshoe and Roosevelt)

.

Perciforms. At four breeding territories contain-

ing reservoirs (Bartlett, Saguaro, Horseshoe, and

Roosevelt), we recorded delivery of 61 largemouth

bass, 51 black crappie, 41 yellow bass, and 14 oth-

ers (mainly sunfish). Eagles obtained these perci-

forms mainly as carrion from the reservoir or as

they lay moribund at the surface. Of 76 dead or

moribund perciforms found in carrion surveys onthese same reservoirs, 29 were yellow bass, 15 large-

mouth bass, 13 black crappie, eight bluegills, four

smallmouth bass, four green sunfish, and three

walleye. The yellow bass and black crappie were

apparent victims of spawning stress, whereas manyof the largemouth fatalities were angler-related.

Birds and Mammals. Coots were attacked whenthey foraged in the grassy shallows of reservoirs.

Eagles caught grebes and waterfowl either by

stooping repeatedly at groups in open water or by

approaching low (<1 m) over the surface, snatch-

ing the prey in passing. We observed no attempts

at live mammals.

Habitat Use. We observed eagles foraging in rif-

fles disproportionate to their occurrence along ihe

river. At Ladders, 54% of 58 prey captures were in

riffles, the latter composing only 5% of riverine

habitat within the 22-km foraging range of the ea-

gles. At East Verde, 46% of 61 observed foraging

events were in riffles, compared to 15% availability

within 19 river km. Along 2-3 kilometers of river at

Bartlett, 73% of 119 observed foraging attempts

were in riffles compared with 8% availability. At

Blue Point, 32% of 28 attempts were in riffles com-

pared with 4% availability. The frequency of riffle

use in part reflected the high proportion of sucker

captures in those territories. As noted, eagles cap-

tured suckers mainly in riffles, carp most often in

runs, and channel catfish in pocket water and runs.

In 162 measurements of turbidity at strike points

for live fish, 136 (84%) were in water that was

“clear to the bottom.” When rivers became turbid

during prolonged periods of snowmelt, eagles

tended to forage elsewhere, such as in clear trib-

utaries.

At the four breeding areas containing both riv-

erine and reservoir environments, eagles mostly

foraged from reservoirs (>50% of locations). At

two territories where eagles nested on the river 3.6

km and 7.0 km from reservoirs, 51% and 61% of

total relocations were on the reservoirs, respective-

ly. For a radio-tagged pair whose nest was situated

where a river entered a reservoir, 85% and 86% of

relocations were on the reservoir. At a territory

where the nest was about 2 km from both river and

reservoir, 59% of relocations were on the reservoir.

Among a biomass total of 113.5 kg of delivered

prey items recorded at these four territories,

28.4%, 65.9%, 93.9%, and 48.4% were obtained

from the reservoir. Of 641 forage attempts record-

ed at these territories, 386 (60%) were on reser-

voirs.

Foraging Range. Free-flowing river. We comparedeagle foraging ranges at two territories (Ladders

and East Verde) situated on the free-flowing Verde

River far upstream of the dams and reservoirs (Fig.

1). The nests of both pairs were on cliffs overlook-

ing the river: the two nests at Ladders were directly

over bar-riffles, but the East Verde nest was about

1 km from the nearest bar-riffle. At both territo-

ries, the null hypothesis of random selection by the

eagles of 1-km segments containing bar-riffles was

rejected (Chi-square tests, P < 0.005). At East

Verde, 72% of mainstem relocation points were

within seven 1-km segments, in the aggregate con-

taining 100% of the bar-riffles within the 19 km

252 Hunt et ajl. VoL. 36, No. 4

*34 37« ^36 137 153 1' UO U’

(0 14

|„UJ2 10«

S 8oc 6d)

g 40.

Fast Verde Male

494 relocations

124 125 ‘>7 Ti ' -

Bar Rime

-

I

V'erde River ^ 'tritaiHries'

''Q"_ tribSy Vei4e River

Figure 2. Foraging range of the radio-tagged breeding male Bald Eagle at the East Verde territory. Relocation

percentages in the nest vicinity were adjusted according to the proportion of observed prey deliveries from those 1-

km segments (see Methods) . Open bars quantify cases in which trackers could not precisely locate the eagles; dotted

lines extending laterally from open bars indicate zones of eagle occupancy for the imprecise locations (tributary

relocation percentages not shown).

foraging range (123-141 km), but containing only

21% of the available channel-riffle habitat (Fig. 2).

At Ladders, 54% of visits within the 22 km range

were within the six 1-km segments containing bar-

riffles.

There were clear, seasonal shifts in prey and hab-

itat use (Fig. 3). For example, in March, when the

Verde River was turbid, 17 of 18 prey items record-

ed at the East Verde territory were mammals. In

April, the East Verde male traveled up two relative-

ly clear tributaries to forage on spawning suckers.

By early May, he was foraging almost exclusively in

the mainstem Verde River, taking carp and catfish.

His use of river sections downstream of the nest

peaked during the mid-point of the brood cycle,

then shifted dramatically to the area upstream of

the nest containing a large bar-riffle.

Regulated river and reservoir. The home ranges of

the Bartlett and Blue Point pairs (29 and 26 river-

km, respectively) both contained a deep-release

(cool) regulated river section below a reservoir fed

by a regulated reach. At both breeding territories,

90

(AC

80

70

8 60

O<D 500^

O 40•4—

•

5 30UO 200-

10

Downstream from Nest

Upstream from Nest

H Tributaries

P1-9 April

Af =49

ali

14-23 April

N =60

28 April - 7 May

N = 109

13-21 May 26 May - June 4

A/ = 137 A/ = 121

Figure 3. Chronological shifts in ranging by the radio-tagged male at the East Verde territory to areas outside the

nest vicinity.


most river visits by radio-tagged eagles were in the

vicinity of the first large cliff downstream of the

respective dams. Suckers were abundant in riverine

environments at both territories. At Bartlett, a

large bar-riffle was present near the nest cliff. This

1-km segment and the only two others containing

bar-riffles received the three highest relocation

scores (51%, 8%, and 8% of 164 river relocations

of the male) within a home range containing 13

km of river. At Blue Point, the 1-km segment with

the highest river relocation score (56% of 314 river

relocations of the male in two breeding seasons)

contained a large cliff above a bar-riffle. At both

territories, the eagles traveled downstream as far as

9 km to forage on suckers in early spring, but as

the zones of suitable sucker spawning tempera-

tures moved upstream, the birds responded ac-

cordingly. At Bartlett, this phenomenon is appar-

ent when one divides the 1989 nesting season (26

February-20 May) into three equal periods. In the

early period, 35% of relocations by the breeding

male were to the area within about 2 km of the

nest (3.6 km downstream of the dam), but these

rose to 59% and 86% in the middle and late pe-

riods. Relocations to the area 3-10 km downstream

of the nest declined from 65% to 36% to 14% dur-

ing the three periods. In 20 comparisons of river

temperatures between the nest vicinity and a lo-

cation about 5 km downstream, the downstream

temperatures were invariably higher (paired t-test,

t = 11.3, P < 0.0001). During the early period

when the eagle traveled downstream so frequently,

the mean stream temperature was 13.5°C at the

nest vicinity and 15.5°C at the downstream loca-

tion. Importantly, Sonora suckers spawn at 14-

18°C. Sucker spawning peaked in the downstream

reach in mid-March and ceased by mid-April, whenspawning in the upstream section reached its peak.

Both the Bartlett and Blue Point eagles frequent-

ly perched and foraged in reservoir environments:

51% of 334 relocation points by the Bartlett male

were on the reservoir, and 59% {N — 765) for Blue

Point. Waterbirds (mainly American Coots and

Eared Grebes) attracted eagles at both territories

to the reservoir in winter. In spring, the main in-

ducement for reservoir use in both areas was the

presence of carrion (or moribund) fish, mainly yel-

low bass (Saguaro), black crappie (Bartlett), and

largemouth bass (both reservoirs).

Free-flowing river and reservoir. The Horseshoe and

Pinal breeding territories both contained a free-

flowing river section that entered a reservoir. The

Horseshoe nest was at the upstream end of a res-

ervoir, and the Pinal nest was 7 airline km up-

stream of a reservoir. All four radio-tagged adults

foraged primarily at the reservoir inflow. Even

though the Horseshoe nest was at the inflow, the

use of the river was relatively low (male = 15%,female = 18%). Resources offered by these reser-

voirs included wintering waterbirds and carrion

fish. As in the other four territories, the radio-

tagged birds at Horseshoe and Pinal changed their

patterns of home range use during the course of

the nesting season. In winter, the Horseshoe andPinal adults traveled downstream to the body of

the reservoir where waterbirds were concentrated.

By March they began foraging closer to the nest,

and both pairs traveled further to forage during

the late stages of the nesting season. Home range

sizes for the Horseshoe and Pinal pairs were 17 and

27 river-km, respectively.

Environmental Setting and Nesting Success. Wecompared reproductive performance for the peri-

od 1980-90 among breeding territories (produc-

tive at least once during that period) in modified

versus unmodified environments. Productivity

(mean young fledged ±SE/nest year) of pairs mareas altered by dam construction (1.07 ± 0.11, N— 12 territories, 89 nest-years) was almost identical

to that of pairs in areas not altered by dams (1.04

± 0.10, N = 9 territories, 71 nest-years) (t — 0.08,

P = 0.94).

Discussion

Bald Eagle pairs foraged on a wide variety of

prey, the distribution within each diet was rarely

skewed toward a single taxon. If anything, we un-

derestimated the degree of dietary diversity by

lumping some taxonomic groups, by underrepre-

senting the pre-egg-laying diet when birds and

mammals made important contributions to fat stor-

age, and by not including the 4-9-wk post-fledging

period when dependent young remained in their

natal territories. Our results were consistent with

those of Grubb (1995) who hypothesized that

mammals may help to fill a dietary gap during pe-

riods of high turbidity (e.g., snowmelt) when fish

are less visible.

Underlying the diverse and variable diet of nest-

ing eagles were the ordering of gross habitat fea-

tures within the landscape (e.g., reservoirs, rivers,

tributaries), the variety of aquatic habitats within

them (e.g., riffles, runs, pools, reservoir inflows),

the changing factors that influenced the timing of

254 Hunt et at. VoL. 36, No. 4

prey availability (e.g., flow, temperature, and tur-

bidity),and the diverse natural history of each prey

species (e.g., spawning cycles, foraging behavior).

Our radio-tracking data and observations of prey

deliveries at the intensively studied territories sug-

gested that prey sources for nesting eagles rarely

remained constant throughout the reproductive

cycle.

Our findings support that prey and habitat di-

versity are important to many Bald Eagle pairs in

Arizona, allowing for continuous food availability

through a lengthy breeding season. Thus, it would

seem that dams may benefit Bald Eagles to the ex-

tent of creating water temperature discontinuities

and additional aquatic habitats, some with large

populations of fish. However, environments modi-

fied by dams were not necessarily better for Bald

Eagles than those on free-flowing river reaches,

given that reproduction in the two settings was

nearly identical. Eagles do appear to benefit from

the presence of exotic fish which form major com-

ponents of the eagles’ diet in both regulated and

unregulated environments.

Even so, current conditions are not necessarily

more supportive of Bald Eagles than were those in

the pristine (pre-livestock) landscape when morerobust, infiltrated soils likely slowed the transport

of water to rivers which thereby maintained moreconsistent flows over the yearly cycle of rainfall

(Olmstead 1919, Hastings 1959, Hastings andTurner 1965, Hayden 1965). Moreover, somestream courses, now seasonally dry, were perennial

in past centuries and doubtless supported fish pop-

ulations. Since the 1980s, at least nine pairs of Bald

Eagles have fledged young on free-flowing reaches

and tributaries that are probably now more turbid

than they would have been before the grazing era.

Today, Bald Eagles nesting upstream of reser-

voirs feed primarily on four fish species: Sonora

suckers, desert suckers, carp, and channel catfish.

Of these, only the suckers are native to Arizona.

However, five other species of hsh of appropriate

size categories were once present: Colorado pike-

minnow {Ptychocheilus lucius)

,

razorback sucker {Xy-

rauchen texanus), flannelmouth sucker { Caloslomus

latipinnis), roundtail chub (still fairly common),and bonytail chub {Gila elegans) (Minckley 1973).

Several reports attest to the early abundance of na-

tive fishes (Rostlund 1952, Minckley and Alger

1968, Haase 1972). Native Americans used themextensively for food, as did the settlers that cameto the region in the mid-1800s (Davis 1982). Even

as late as the early 1900s, fish were so common in

the lower Salt and Gila rivers that they were sold

as feed for domestic animals and as fertilizer

(Minckley 1973). Now, the Colorado pikeminnow,

the razorback sucker, and the bonytail chub are

federally listed as endangered.

Although we cannot be certain if the commu-nities of native fishes occurring in the pristine riv-

ers supported nesting eagles, it is quite possible

that the four species of suckers, augmented by wa-

terfowl and spawning runs of pikeminnow and pos-

sibly others, formed a complete prey base. Because

suckers feed and spawn in shallow water, they are

ideal prey for eagles. Our study suggests that eagles

would have benehted if the native fishes were to

have spawned at different times. Such would be

expected, considering that any coevolved commu-nity of fishes would tend toward spawning differ-

entials in time and space (some ascending tribu-

taries) because of niche similarity and competition

among fry.

ACKNOWI.EDGMENTS

The U.S. Bureau of Reclamation (USBR) funded this

work. We acknowledge the cooperation of the Arizona

Game and Fish Department (AGFD), U.S. Fish and Wild-

life Service (USFWS), Arizona Bald Eagle Nest WatchProgram, Salt River Project (SRP), U.S. Forest Service

(USFS), Bureau of Land Management (BUM), Bureau of

Indian Affairs, and the San Carlos Apache, White Moun-tain Apache, Fort McDowell, and Salt River Pima-Mari-

copa tribes. We are grateful to D. Busch, T. Gatz, M. Jakle,

and FI. Messing (USBR) who provided direction and as-

sistance throughout the project. We also thank R. Glinski,

T. Tibbitts, J. Janish (AGFD), R. Hall (BLM), D. Reigle

(SRP), and A. Harmata for help and guidance. Special

thanks are extended to R. Mesta (USFWS) for help with

data collection. G. Harris, J. Rassi, M. Greenburg, and D.

Blakely (SRP) negotiated SRP helicopter assistance for

nest climbs. D. Stewart, T. Noble, M. Ross, R. Kvale, D.

Pollock, and D. MacPhee (USFS) provided logistical sup-

port. For radio-tracking, observation, and fisheries work,

we thank BioSystems Analysis, Inc. employees G. Ahl-

born, G. Beatty, P. Becker, V. Behn, B. Bock, P. Carroll,

M. Cashman, D. CIcndenon, M. Cross, J. Driscoll, F. Fioc-

chi, A. Gertstell, J. Gilardi, F. Hein, C. Himmelwright, A.

Klatzker, P. fang, F. Lapsansky, M. Larscheid, C. I.enihan,

D. Ledig,J.Linthicum, S. Marlatt, J. Meyers, D. Monda,

N. Nahstoll, C. Page, R. Spaulding, D. Stahlecker, K.

Thompson, L. Thompson, R. Thorstrorn, D. VonGonten,

and K. VonKugelgen. For help with identification of prey

remains, we thank R. Cole, R. Miller, G. Smith, Y Petry-

szyn, P. Krausman, and C. Schwalbe. We thank P. Law for

help with statistics and J. linthicum, T. Hunt, A. Har-

mata, R. Steidl, and T. Grubb for comments on the man-uscript.


Literature Cited

Becker, G.C. 1983. Fishes of Wisconsin. Univ. of Wiscon-

sin Press, Madison, WI U.S.A.

Brown, D.E. 1998. Habitats of Arizona raptors. Pages 10-

17 in R.L. Glinski [Ed.], The raptors of Arizona, Univ.

of Arizona Press, Tucson, AZ U.S.A.

Carlander, K.D. 1969. Handbook of freshwater hshery

biology. Vol. I. Iowa State Univ. Press, Ames, lA U.S.A.

. 1977. Handbook of freshwater fishery biology.

Vol. II. Iowa State Univ. Press, Ames, lA U.S.A.

Davis, G.P. 1982. Man and wildlife in Arizona: the Amer-

ican exploration period, 1824-1865. Arizona Gameand Fish Department, Phoenix, AZ U.S.A.

Driscoll, D.E., R.E. Jackman, W.G. Hunt, G.L. Beatty,

J.T Driscoll, R.L. Glinski, T.A. Gatz, and R.I. Mes-

TA. 1999. Status of nesting Bald Eagles in Arizona. J.

Raptor Res. 33:218-226.

Edwards, T.C., Jr. 1988. Temporal variation in prey pref-

erence patterns of adult Ospreys. Auk 105:244-251.

Grubb, T. 1995. Food habits of Bald Eagles breeding in

the Arizona desert. Wilson Bull. 107:258-274.

Haase, E.F. 1972- Survey of floodplain vegetation along

the lower Gila River in southwestern Arizona.J.

Ariz.

Acad. Sci. 7:75-81.

Hastings, J.R. 1959. Vegetation change and arroyo cut-

ting in southeastern Arizona./. Ariz. Acad. Sci. 1:60—

67.

and R.M. Turner. 1965. The changing mile.

Univ. of Arizona Press, Tucson, AZ U.S.A.

Hayden, C. 1965. A history of the Pima Indians and the

San Carlos irrigation project. U.S. Gov. Printing Of-

fice, Washington, DC U.S.A.

Haywood, D.D. and R.D. Ohmart. 1986. Utilization of

benthic-feeding fish by inland breeding Bald Eagles.

Condor 88:35-42.

Hunt, W.G., J.M. Jenkins, R.E. Jackman, C.G. Thelan-

der, and A.T. Gerstell. 1992. Foraging ecology of

Bald Eagles on a regulated river./. Raptor Res. 26:243-

256.

AND P.R. Law. 2000. Site-dependent regulation of

population size: comment. Ecology 81:1162-1165.

Jackman, R.E., W.G. Hunt, D.E. Driscoll, and J.M. Jen-

kins. 1993. A modified floating-fish snare for capture

of inland Bald Eagles. N. Am. Bird Bander 18:98-101

, W.G. Hunt, D.E. Driscoli., and F. Labsansky.

1994. Refinements to selective capture techniques for

Bald and Golden Eagles. / Raptor Res. 28:268-273.

, W.G. Hunt, J.M. Jenkins, and PJ. Detrich. 1999

Prey of nesting Bald Eagles in northern California /Raptor Res. 33:87-96.

Jamieson, L, N.R. Seymour, and R.P. Bancroit. 1982.

Use of two habitats related to changes in prey avail-

ability in a population of Ospreys in northeastern

Nova Scotia. Wilson Bull. 94:557-564.

Kenward, R.E. 2001. A manual for wildlife radio tagging.

Academic Press, London, U.K.

Lowe, C.H. (Ed.). 1964. The vertebrates ofArizona. Univ

of Arizona Press, Tucson, AZ U.S.A.

McClelland, B.R., L.S. Young, P.T. McClelland, J G.

Crenshaw, H.L. Allen, and D.S. Shea. 1994. Migra-

tion ecology of Bald Eagles from autumn concentra-

tions in Glacier National Park, Montana. Wildl. Mon-

ogr. 125:1-61.

Minckley, W.L. 1973, Fishes of Arizona. Arizona Gameand Fish Department, Phoenix, AZ U.S.A.

AND N.T. Alger. 1968. Fish remains from an ar-

chaeological site along the Verde River, Yavapai Coun-

ty, Arizona. Plateau 40:91-97.

Olmstead, F.H. 1919. A report on flood control of the

Gila River in Graham County, Arizona. U.S. Gov.

Printing Office, Washington, DC U.S.A.

Rostlund, E. 1952. Freshwater fish and fishing in native

North America. Univ. Calif. Publ. Geogr. 9:1-313.

Royama, T. 1970. Factors governing the hunting behav-

iour and selection of food by the Great Tit {Parus

major).J.

Anim. Ecol. 39:619-668.

Todd, C.S., L.S. Young, R.B. Owen, Jr., and FJ. Gram-

LICH. 1982. Food habits of Bald Eagles in Maine /Wildl. Manage. 46:636-645.

Van Daele, L.J. and H.A. Van Daele. 1982. Factors af-

fecting the productivity of Ospreys nesting in west-

central Idaho. Condor 84:292-299.

Vannote, R.L., G.W. Minshaiu, K.W. Cummins, J.R. Se-

DELL, and C.E. Cushing. 1980. The river continuum

concept. Can. f.Fish Aquatic Sci. 37:130-137.

Received 26 March 2001; accepted 6 September 2002

J. Raptor Res. 36(4) :256-264


VERNAL MIGRATION OF BALD EAGLES FROM A SOUTHERNCOLORADO WINTERING AREA

Alan R. Harmata^Fish & Wildlife Program, Department ofEcology, Montana State University, Bozeman, MT 59717 US.A.

Abstract.—^Adult Bald Eagles {Haliaeetus leucocephalus) {N =15) wintering in the San Luis Valley (SLV),

Colorado were radio-tagged with conventional tail-mounted transmitters between 1 January-18 March

1980 and 1981 to determine migration patterns and breeding areas. Migrating eagles were followed

primarily in a single vehicle with two trackers. In 1980, radio-tagged eagles (N = 4) left the wintering

grounds within a 15-d span in March but departures in 1981 (N = 7) ranged from mid-February to

early April. Eagles initiated migration on days with higher temperature ranges, more clouds, and higher

winds than other days during winter or spring. Subsequent travel paralleled the northward movementof the 2°C isotherm both temporally and spatially. Locations and pathways of migrating eagles were

similar in both 1980 and 1981. All four eagles located on their summer range were within 102 km of

each other in northeastern Saskatchewan and northwestern Manitoba. Mean distance from the SLVwintering area to breeding or summer areas of Bald Eagles was 2019 km. Adult Bald Eagles apparently

migrated alone in spring with mated males leaving first. Migration flights began between 1015-1045 HMST and ended between 1715-1745 H. Mean daily movement was 180 km. Migration flight speeds

averaged about 50 km/hr. Altitude of flight ranged from 30-4572 m above ground level (AGL), but

most often was between 1500-3050 m.

Key Words: Bald Eagle; Haliaeetus leucocephalus; Colorado; radio-tracking, Saskatchewan; vernal migration;

wintering.

MIGRACION PRIMAVERAL DE LAS AGUILAS CALVAS DESDE UN AreA DE INVERNACION ALSUR DE COLORADO

Resumen.—Individuos adultos de aguila calva {Haliaeetus leucocephalus) {N = 15) invernando en el valle

de San Luis (VSL) Colorado, fueron provistos con radios transmisores convencionales montadc^s en la

cola, entre el 1 de enero-18 de marzo de 1980 y 1981 para determinar los patrones de migracion y las

areas de reproduccion. Las aguilas en migracion fueron seguidas en primera instancia en un vehiculo

sencillo con dos rastreadores. En 1980, las aguilas con radios {N = 4) abandonaron los campos de

invernacion en un intervalo de 15 dias en marzo, pero las partidas en 1981 {N = 7) fueron entre

mediados de febrero y principios de abril. Las aguilas iniciaron la migracion en dias con ranges de

temperaturas mas altos, mas nubes, y vientos mas altos que otros dias durante el invierno o primavera.

El subsiguiente vuelo fue paralelo al movimiento hacia el norte de la isoterma 2°C tanto temporal comoespacialmente. Las localizaciones y vias de paso de las aguilas migratorias fueron similares en 1980 y

1981. Las cuatro aguilas localizadas en su rango de verano estuvieron dentro de 102 km una de otra

en el nororiente de Saskatchewan y noroccidente de Manitoba. La distancia media desde el area de

invernacion del VSL a las areas de reproduccion o de verano de las aguilas calvas fue de 2019 km. Las

aguilas calvas adultas aparentemente migraron solas en primavera mientras que sus machos pareja sal-

ieron primero. Los vuelos de migracion comenzaron entre 1015-1045 H MST y terminaron entre 1715-

1745 H. El movimiento medio diario fue 180 km. Las velocidades de los vuelos durante la migracion

tuvieron un promedio de 50 km/h. La altitud de vuelo tuvo un rango entre 30-4572 m.s.n.m. pero la

mayoria a menudo estuvo entre 1500—3050 m.


Relatively stable wintering populations of Bald

Eagles {Haliaeetus leucocephalus) existed in the San

Luis Valley (SLV) of southern Colorado through-

^ E-mail address: [email protected]

out the DDT era (Ryder 1965, Alamosa National

Wildlife Refuge reports 1954-83). In the 1970s, a

mean of 185 (SD = 66.6) Bald Eagles was counted

in the SLV annually (V= 5; Craig 1981). However,

origins of eagles wintering in the SLV were un-

known.

256

December 2002 Bai d Eagle Vernal Migration 257

Between December—April 1977 and 1978, win-

tering Bald Eagles (N = 36) in the SLV were

marked with yellow patagial wing markers to de-

termine their geographic origins or breeding areas

(Harmata and Stahlecker 1993). Colormarking re-

vealed fidelity of individual Bald Eagles to this win-

tering area was high, but by January 1981 only

three sightings of yellow-marked eagles occurred

outside the SLV and none were in a documentednesting area or during summer (Harmata and

Stahlecker 1993). The primary objective of the

marking program had not been realized. Clearly,

other methods were required to achieve objectives

in a timely and cost-efficient manner.

Prior to the 1980s, technology for remotely

tracking long-range movements of individual birds

(i.e., satellite platform transmitter terminals or

PTTs) was not available. However, on 28 February

1978, after being tracked locally for nearly six

weeks, an adult Bald Eagle wearing a conventional,

tail-mounted transmitter left her SLV wintering

area. She was tracked for two days over 300 kmthrough the most rugged portion of the Rocky

Mountains, being lost only due to lack of logistical

planning, not our ability to maintain contact. This

serendipitous event revealed the potential of de-

termining migration routes and breeding areas of

Bald Eagles using conventional radio-tracking. This

paper discusses results of subsequent long-range

tracking of Bald Eagles with conventional teleme-

try from one seasonal range to another prior to

widespread use of PTTs on eagles (e.g., Grubb et

al. 1994, Brodeur et al. 1996, Meyburg et al. 2001).

Objectives of this study were: (1) to determine

breeding areas of adult Bald Eagles wintering in

southern Colorado and (2) to gather information

regarding factors associated with initiation of ver-

nal migration, routes, duration, stopover habitats

used, and other factors affecting the successful

completion of migration.

Study Area and Methods

The SLV is the largest and most southern of four large

intermountain basins in Colorado. Encompassing 6475

km^, the SLV is approximately the size of the state of

Delaware. Mean elevation of the nearly-level valley floor

IS 2286 masl. High (>3050 m) mountain ranges border

the valley on east and west, merging at the northern end.

The Rio Grande and Conejos rivers flow through the SLVand numerous natural warm springs and wetlands that

seldom freeze have made the SLV attractive to waterfowl

and Bald Eagles, probably for millennia. Water develop-

ments and agriculture in the 20th century have probably

improved the attractiveness.

Between 7 January-18 March 1980 and 1981, 15 adult

Bald Eagles were captured and radio-tagged in the SLVAll were captured by a modified “Lockhart” method(Miner 1975) with and without live Bald Eagle and Gold-

en Eagle {Aquila chrysaetos) lure birds. Trap sites werechosen on the basis of frequency and duration of the

presence of two adult Bald Eagles of distinctly dissimilar

size, presumably mated, within 1.6 km. In 1981, I esti-

mated the SIV winter population at 170 Bald Eagles

(Harmata 1984).

Gender of radio-tagged eagles was assigned by methodspresented by Garcelon et al. (1985). Three were con-

firmed by behavior during copulation. All Bald Eagles

were radio-tagged with two-stage radio transmitters

mounted proximo-ventrally on the tail. Transmitter fre-

quencies were between 148.500 and 148.950 mHz. Unitlife expectancy was ^5 mo. Transmitter, antenna, andmounting tab weighed 50-57 g. Telemetry receiving

equipment included fixed channel and programmablereceivers.

Mated status of radio-tagged Bald Eagles was deter-

mined by frequency and duration of time spent in the

presence of another adult eagle of distinctly dissimilar

size, observed copulation {N = 3) in the SLV, or associ-

ation with a nest site on the breeding grounds {N = 2).

Eagles were considered unmated if diurnal movementsin the SLV were clearly independent of other eagles andthey were not observed to roost away from communalroosts with just one other eagle, as mated birds often did

Climatological data associated with days that Bald Ea-

gles left the SLV were analyzed by stepwise discriminate

analysis (Dixon 1981) to investigate meteorological con-

ditions associated with initiation of vernal migration. Cli-

matological data recorded near the geographical center

of the SLV (Alamosa, Colorado) were obtained from Na-

tional Oceanographic and Atmospheric Administration,

Asheville, North Carolina Monthly Summary Sheets. Datafor days that eagles left the SLV were compared to data

for days randomly selected between 1 January-15 April

1980 and 1981 that they did not. Variables selected for

comparisons among days were maximum, mean, andrange of temperature, percent of clear sky and meanwind speed.

Migrating eagles were followed primarily from a single

4X4 vehicle with two human trackers and a dog. Anomnidirectional antenna and two element “H” yagi re-

ceiving antenna were mounted on the roof of the chase

vehicle. The yagi was attached to a 360° traversing mount,allowing for directional tracking while the vehicle was

moving. Manpower and logistic limitations plus variability

in departure dates, routes, and travel speeds of Bald Ea-

gles prevented ground tracking of more than one eagle

at a time. One tracker drove while the other operated

the receiving equipment. Both shared navigational du-

ties. Due to often high chase speeds (up to 150 km/hr)and off-road “adventures,” visual contact with migrating

eagles could not be maintained, so migration behavior

often could not be recorded continuously, accurately, or

safely. Route, direction, and speed of the chase vehicle,

therefore, often was selected primarily to maintain max-imum audio signal strength. When contact with a mi-

grating eagle was lost, an aerial search was implementedusing local air services, A two or three element yagi an-

258 Harmata VoL. 36, No. 4

FEMALES O O O • •

MALES O o

-40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15

DAYS FROM VERNAL EQUINOX

Figure 1. Days from vernal equinox that radio-tagged Bald Eagles departed {N= 12) their San Luis Valley, Colorado,

winter ranges to initiate vernal migration, 1978 {N = 1), 1980 (N = 4), 1981 {N = 7). Open circles indicate eagles

determined to be unmated, closed circles indicate eagles that were mated (see text), and square indicates eagle of

undetermined mated status.

tenna was taped to the wing strut (high wing) or step

(low wing) of light aircraft and the area surveyed in tran-

sect style with intermittent, “lazy” circles at high altitude.

Frequencies were scanned to search for the target eagle

and other potential migrating birds. When contact was

reestablished and eagle’s status discerned as stationary,

vehicle tracking resumed. Flight altitudes were estimated

based on eagle’s position relative to the search aircraft

and trees, geography, and structures such as buildings

and radio towers while ground tracking. Eagles weremonitored in their summering grounds with Beaver air-

craft, snow machines, and snow shoes.

Results and Discussion

Initiation of Migration. Over half (58%) of ra-

dio-tagged Bald Eagles with known departure dates

(N = 12), initiated vernal migration within one

week after the vernal equinox (Fig. 1). In 1980,

radio-tagged eagles {N — 4) all left the wintering

grounds within a 15-d span in March (Table 1).

Range of known departure dates {N — 8) spanned

50 d in 1981, with the first confirmed departure of

Table 1. Residency and mated status of radio-tagged adult Bald Eagles with known departure dates from winter

ranges in the San Luis Valley (SLV), Colorado.

Eagle

Designation Sex Captured

Date

Departed SLVMatedStatus'*

MinimumResidency

in SLV(davs)

378 F 21 Jan. 1978 28 Feb. 1978 U 39

180 F 18 Jan. 1980 21 Mar. 1980 M 63

280 M 23 Jan. 1980 24 Mar. 1980'^ M 61

380 M 23 Jan. 1980 21 Mar. 1980 M 58

480 M 27 Jan. 1980 8 Mar. 1980 U 41

181 F 7 Jan. 1981 11 Feb. 1981 u 36

281 M 9 Jan. 1981 20 Feb. 1981 u 43

381 F 9 Jan. 1981 27 Mar. 1981 M 78

481 M 11 Jan. 1981 27 Mar. 1981 M 76

581 F 15 Jan. 1981 25 Mar. 1981 U 70

881 M 15 Mar. 1981 21 Mar. 1981 ?*' 7

981 F 18 Mar. 1981 1 Apr. 1981 M 15

M = mated, U = unmated (see text).

First departed on 22 March 1980, but eagle encountered a winter storm and returned to winter range.

Undetermined.

December 2002 Bald Eagle Vernal Migration 259

Table 2. Mean climatological values (±99% confidence

interval) which discriminated {P ^ 0.01) between days

radio-tagged Bald Eagles initiated northward migration

from their San Luis Valley, Colorado wintering area (De-

part) and days they did not (Remain).

Tempera-

TURE Percent WindRange Sky Speed

(°C) Clear (km/hr)

Depart {N = 11) 24 (5) 50 (26) 22 (5)

Remain {N = 21)=* 19 (4) 56 (20) 16 (5)

Randomly selected.

a radio-tagged eagle occurring in mid-February

and the last in early April (Table 1). Number of

days from the equinox that eagles departed was not

different between genders (Mann-Whitney U =

16.50, P — 0.81). However, mated eagles departed

the SLV closer to the equinox and later than un-

mated eagles (Mann-Whitney U = 3.00, P = 0.03;

Fig. 1).

Three climatological variables discriminated be-

tween days that radio-tagged Bald Eagles left the

SLV on migration and those they did not (Table

2). Eagles initiated migration on days with muchlarger range of temperatures, more clouds, and

with higher winds than other days over the winter-

spring period. Migration tended to be initiated

about 5 hr after sunrise regardless of the immedi-

ate meteorological condition.

Photoperiodism is considered to be the ultimate

stimulus for the onset of migration in birds (King

and Earner 1963). All radio-tagged Bald Eagles de-

termined to be mated left the SLV within 12 days

of the vernal equinox, indicating breeding adults

may be sensitive to equal periods of light and dark.

Unmated, nonbreeding, or immature eagles maybe equally sensitive but may not be driven by pres-

sure to procreate. In fact, first observations of sub-

adult eagles in northern ranges both years were

not until at least two weeks subsequent to the ar-

rival of the first radio-tagged adults. Migrational

movement also paralleled the northward move-

ment of the 2°C isotherm (Lincoln 1979) both

temporally and spatially, hinting that thermal cues

may also be involved in the initiation of migration.

Once the urge is kindled, proximate affectors of

Bald Eagle migration appear to be coincident with

incoming low pressure systems, associated wide

range of temperatures, cyclonic air flows, and

southerly winds; similar to conditions noted by

Bagg et al. (1950) for other birds.

Although Bald Eagles are apparently sensitive to

local conditions when migration is initiated, they

appear to be cognizant of little beyond their im-

mediate environs. Eagle 280 departed the SLV on

22 March 1980 and traveled 145 km north before

being stopped by severe snow squalls. He spent the

night on a mountain pass and as the storm per-

sisted to the north the next day, he returned to his

winter range in the valley. He spent the remainder

of that day and part of the next in close association

with a female (distinctly larger eagle) and was ob-

served to copulate during this period. He initiated

migration again on 24 March, leaving the SLV for

the season.

Migration Routes, Destination, and Navigation.

In 1980, a relatively narrow migration corridor

through Colorado, Wyoming, and Montana was

used by three radio-tagged eagles (Fig. 2). Eagle

380 became sedentary in north-central Saskatche-

wan after 15 d of migration, six of which were

spent sitting out bad weather. After four days of

almost continual solitary soaring, he was found

perched close to a larger eagle where he remained

for several hours. The next day the pair began con-

struction of a new nest on Chachukew Lake, north

of Pelican Narrows, Saskatchewan. They eventually

fledged one young in August 1980.

In 1981, eagle 281 left the SLV on 20 February,

and was followed for two days over 302 km through

the mountains of western Colorado (Fig. 3) . Direc-

tion was primarily northwest and 281 was the only

eagle tracked that crossed the Continental Divide.

Subsequent tracking of 281 was interrupted be-

cause a radio of the same frequency and pulse rate

as 281 was tracked for a day before I discovered it

was a transmitter on a collar of a bighorn sheep

( Ovis canadensis)

.

Eagle 981 left the SLV on 1 April and was fol-

lowed to about 65 km north of Casper, Wyoming,where she was lost in a snow storm because roads

became impassable. Eagle 481 was detected ap-

proaching Fort Peck Reservoir in east-central Mon-tana on 5 April. After leaving Fort Peck Reservoir,

481 flew due north about 35 km then gradually

shifted to a northwest course. This route took himdirectly to the Missouri Coteau, a ridge line run-

ning longitudinally for over 150 km in southwest-

ern Saskatchewan. He continued north along the

Coteau for about 100 km. Approaching the Cana-

dian Shield, 481 made a sudden change in course


Figure 2. Partial migration routes of radio-tagged adult

Bald Eagles from winter ranges in the San Luis Valley,

Colorado in 1978 and 1980. Numbers indicate eagle des-

ignation and year (Table 1). Summering area of eagle

380 is indicated by 0 (confirmed nest location).

from north to northeast, paralleling the direction

of many elongated lakes and rivers in the Canadian

Shield country. Eagle 481 was subsequently fol-

lowed to Reindeer Lake, Saskatchewan, arriving on

10 April. On 22 April, 481 was found by air asso-

ciated with a nest site on Ramuchawie Lake in west-

ern Manitoba near the Saskatchewan border (Fig.

3).

Aerial surveys covering ca. 210000 km^ of north-

ern Saskatchewan were conducted to detect signals

of other SLV Bald Eagles in mid- to late April in

both 1980 and 1981. During aerial surveys, eagle

181 was located on the Pagato River, south of Rein-

deer Lake, Saskatchewan, and eagle 581 was de-

tected briefly in the area of Trade Lake, south of

the Churchill River (Fig. 3). The signal was weak

and intermittent, which indicated either a radio

Figure 3. Partial migration routes of radio-tagged adult

Bald Eagles from winter ranges in the San Luis Valley

(SLV), Colorado in 1981. Numbers indicate eagle desig-

nation (Table 1). Summering areas are indicated by 0(nest locations). Respective 1981 and 1982 recovery lo-

cations of Bald Eagles banded in the SLV (January 1977)

are indicated by (x). Tbe October 1981 recovery location

of a Bald Eagle radio-tagged in the SLV in March 1981

is indicated by 781.

malfunction, a dead eagle, or a bird in incubation

posture. Lack of contact with other SLV eagles mayhave been a function of transmitter failure (one

was known to fail in the SLV),premature shedding

of the transmitter (one transmitter was found still

attached to broken tail feathers below a perch tree

in the SLV),mortality, incomplete survey coverage,

or summering areas were located outside of north-

ern Saskatchewan. However, the fact that 31% of

potentially-detectable eagles (N= 13) were located

within an area roughly the size of Yellowstone Na-

tional Park (ca. 9300 km^) suggests that most adult

Bald Eagles wintering in the SLV originated from

this area of Canada.

December 2002 Bald Eagle Vernal Migration 261

Mean distance (as the eagle flies) from the SLVwintering area to breeding or summer areas of

Bald Eagles was 2019 km {N - 4, SD = 50). All

eagles located on their summer ranges were within

102 km of each other in northeastern Saskatche-

wan or northwestern Manitoba (Figs. 2 and 3). Du-

ration of travel between winter and summer range

for SLV Bald Eagles with known departure and ar-

rival dates {N = 2) was 15 d. Although SLV Bald

Eagles traveled about Vs the distance to their sum-

mer ranges compared to one Bald Eagle tracked

by satellite from Arizona to the Northwest Terri-

tories (3032 km, Grubb et al. 1994), they complet-

ed the journey in only about 40% of the time.

However, the Arizona eagle was a subadult (3rd yr)

and presumably was not driven by the impetus to

nest, as were adult SLV eagles tracked.

Geography, celestial cues, and weather may all

play a role during migration of Bald Eagles. Prom-

inent physiographic features such as deep canyons,

rivers, and north-south oriented topography

seemed to assist in visual navigation during flight

(Griffin 1943). These features could have been im-

printed in the memory of eagles during their ini-

tial migrations and experience dictated direction

during subsequent flights (kinesis theory; Mat-

thews 1963). Imprinting of migration routes from

wintering areas, which compliment survival during

the first year, would be more adaptive than im-

printing during first southward migration.

Eagles did not migrate on days of total overcast,

a phenomenon also noted by Gerrard and Gerrard

(1982). The altitude of the cloud layer may have

an effect, but overcast layers over 90 m were not

experienced during tracking. Sun compass orien-

tation (Kramer 1952, 1957) with time compensa-

tion, commonly referred to as sun-azimuth orien-

tation (Welty 1982) may, therefore, be important

for orientation of adult Bald Eagles during migra-

tion.

True navigation (selection of a compass direc-

tion toward a known goal in unfamiliar territory;

Able 1980) may also be a component of Bald Eagle

migration. Migrating eagles appear to avoid strong

winds during migration because strong winds ap-

parently influence direction of flight. Eagles did

not move, except locally, during days when winds

in excess of 35 km/hr occurred prior to 0900 H.

East winds of 60—80 km/hr began about two hours

after initiation of eagle 380’s flight on one migra-

tion day and his flight path deviated well west of

direct line to the eventual goal. Flight direction for

the remainder of migration clearly compensated

for the one day blown off course (Fig. 2). Unless

tbe eagle had been exposed to the area on previ-

ous migrations, true navigation is indicated. How-ever, it is not unreasonable to assume that an adult

eagle over five years old, may indeed be familiar

with a great portion of western North America as

a result of vagaries of previous migrations. Regard-

less, redundancy in navigational systems has been

illustrated for homing pigeons (Columba livia)

(Able 1980) and in all probability, several backup

navigational systems are available to Bald Eagles,

especially experienced adults.

Migration Behavior. Mated adult Bald Eagles ap-

parently migrated alone in the spring. Eagle 380

was seen roosting solitarily at all but one stopover

location (six other eagles on the Yellowstone River

near Hysham, Montana). Eagle 481 did not mi-

grate with a mate, but often moved northward with

other adult eagles. He roosted with other eagles

three times, but two sites obviously were not com-

munal or traditional because of lack of similarity

to typical Bald Eagle roost sites (Kiester and An-

thony 1983). Paired roosting was probably a result

of facilitatory behavior influenced by poor weather

and lack of daylight remaining. Subsequent obser-

vations of migration flight confirmed he movedalone. Once in the boreal forest of the Canadian

Shield country, local eagles appeared to “meet”

him in flight and escort him through their terri-

tories, but no overt agonistic encounters were ob-

served. Occasional associations with other eagles

appeared incidental for all radio-tagged eagles and

were of short duration. Solitary migration behavior

in established pairs would reduce the possibility of

both members being lost in a local catastrophe.

Daily migration flights consistently began be-

tween 1015-1045 H MST and ended between

1715-1745 H. Mean daily movement was 180 km,

but ranged from 144-435 km {N = 5) in 1980 and33-248 km (A = 5) in 1981. Speed of migration

flights recorded averaged 50 km/hr (A = 7, 22-

144 km/hr in 1980; A = 9, 20-105 km/hr in 1981)

.

Altitude of flights recorded ranged from 30-4572

m AGL, but most often was between 1500-3050 m.

Total distances, speed, and daily duration of mi-

gratory flights indicate that under optimal weather

conditions. Bald Eagles can reach their breeding

grounds within 6 d after leaving the SLV. Penny-

cuick (1975) indicated a 2000 km migration for a

bird the size of a Bald Eagle would be near maxi-

mum attainable without eating, assuming a 25%


mass loss. During this study, no radio-tagged eagles

were observed feeding during migration and meanmigration distance was 2020 km. Captive eagles

commonly fast more than two weeks with no ap-

parent deleterious effects (Brown and Amadon1968, pers. observ.) and wild raptors can lose up

to 30% of body mass without problems (Newton

1979). These compensatory capacities undoubted-

ly allowed adult Bald Eagles to reach their breed-

ing grounds with sufficient energy reserve for

breeding.

All radio-tagged eagles arrived in their summerrange at a time when lakes and most stretches of

rivers were still frozen. The only areas of open wa-

ter were rapids or narrows on rivers or between

lakes. Radio-tagged eagles spent most of their time

there, presumably foraging for fish. Other eagles

observed during aerial surveys were associated with

ubiquitous holes in lake ice and viscera piles of fish

left by native commercial fishing operations. For-

aging eagles were also seen on or near caribou

{Rangifer tarandus) and moose {Alces alces) carcass-

es killed by natives or wolves ( Canis lupus)

.

A few

eagles were seen with snowshoe hare {Lepus amer-

tcanus) remains.

Regional Relationships. McClelland et al. (1994)

noted that Bald Eagles radio-tagged in Glacier Na-

tional Park, Montana, in autumn wintered west of

the Continental Divide and summered in the

MacKenzie River watershed of northern Alberta,

northwest Saskatchewan, and Northwest Territo-

ries. The summer range of a Bald Eagle that win-

tered in Arizona (west of the Divide) also was in

the MacKenzie River watershed (Grubb et al.

1994). McClelland et al. (1994) suggested that win-

tering areas may be related to the watershed of

origin and Bald Eagles be managed by application

of a “Migration Flyway Concept.” Adult Bald Ea-

gles radio-tagged and banded in the SLV wintering

area (east of the Divide) were tracked to breeding

areas in Saskatchewan and Manitoba, all in the

Churchill River watershed. Jenkins et al. (1982) fol-

lowed two adult Bald Eagles radio-tagged in Wyo-

ming during winter. One trapped on the west side

of the Continental Divide was followed to the

MacKenzie River watershed, while one trapped on

the east side of the Divide was followed to the

Churchill River watershed, similar to those from

the SLV. These data suggest a “Churchill-East

Slope” Migration Flyway exists, distinct from the

“Mackenzie-Intermountain” Flyway proposed by

McClelland et al. (1994).

Stopover areas used during vernal migration of

SLV Bald Eagles were generally widely distributed.

A tree of adequate size, secure from human dis-

turbance in any type habitat, was all that seemednecessary for roosting. In late March 1982, Swen-

son (1983) counted 232 Bald Eagles along the Yel-

lowstone River between the mouth of the Bighorn

River and Miles City, Montana. A site where eagle

380 roosted is in the middle of this stretch and

within an area where the river seldom freezes, con-

tained the most highly braided portion of channel,

most heavily wooded islands, and highest Canada

goose {Branta canadensis) populations of three sec-

tions of river studied by Hinz (1974). Use of this

section of the Yellowstone River by adults may be

dictated primarily by tradition and availability of

water, because migrating adults were not known to

feed during this study.

Areas in eastern Montana may be equally im-

portant to as many or more migrating eagles as the

more highly-publicized areas, where ephemeral

concentrations of eagles occur in western Mon-tana. Leighton et al. (1979) estimated a population

of 14 000 Bald Eagles in Saskatchewan. Some ea-

gles from north-central Saskatchewan were cap-

tured in autumn at Hauser Lake (Restani et al.

2000) and Glacier National Park (McClelland et al.

1982), while others passed through eastern Mon-tana during migration (Gerrard et al. 1978, Har-

mata et al. 1985). Both Hauser Lake and Glacier

National Park Bald Eagle concentrations are nowdefunct due to a collapsed, exotic food base (ko-

kanee salmon, Oncorhynchus nerko), but eastern

Montana habitats still support large numbers of na-

tive prey (lagomorphs, ungulates, waterfowl). How-ever, lack of a concentrated food base, diffusion of

roost sites, solitary habits of migrating eagles, plus

dispersion of departure dates from winter (this

study) and summer ranges (Harmata et al. 1985),

prohibit any accurate estimate of numbers of Bald

Eagles passing through eastern Montana. Relatively

low numbers of eagles present at any particular

time at some stopover areas in eastern Montanamay belie the true importance of these areas to

migrating eagles. Turnover of individuals appeared

to be daily, over months. Therefore, western prai-

rie states may provide important migratory habitat

for a large proportion of the continental popula-

tion of Bald Eagles over long periods.

Acknowledgments

J. Stoddart initially suggested Bald Eagle research in

the SLV. Dale Stahlecker served as co-investigator during

December 2002 Bai.d EACiLE Vernai, Migration 263

preliminary marking studies. P. Harmata (then age 5)

helped track the first migrating Bald Eagle in 1978. G.

Montopoli was instrumental for successful completion of

the first year’s migration tracking. M. Lockhart provided

details of eagle capture techniques and field assistance.

S. Werner and E. Spettigue participated in winter andmigration tracking. L. Stevenson of Pelican Narrows, Sas-

katchewan, donated flight expertise and air time. Finan-

cial assistance was provided by R. Koteen; Fred Jense,

Dept, of Veteran’s Affairs; J. Lincer and W. Clark of the

National Wildlife Federation; R. Plunkett of the National

Audubon Society; D. Flath of Montana Fish, Wildlife, andParks; 1.. Jahn of the Wildlife Management Institute andAmerican Petroleum Institute; T. Ingram of Eagle Valley

Environmentalists; S. Rainey and C. Merrit of AmericanWilderness Alliance; M. Malone, Montana State Univer-

sity (MSU) Research Creativity Program; R. Eng, MSUAgricultural Experiment Station; and R. Moore, MSU Bi-

ology Department. T. Crubb, M. Ratine, M. Restani, andD. Stahlecker made helpful comments on earlier drafts

of the manuscript. “Sarge” was the dog, a great compan-ion and a loyal friend.

Literature Cited

Able, K.P. 1980. Mechanisms of orientation, navigation

and homing. Pages 284-373 in S.A. Gauthreaux, Jr.

[Ed.], Animal migration, orientation and navigation.

Academic Press, New York, NY U.S.A.

Bagg, A.M., W.W.EI. Gunn, D.S. Miller, J.T. Nichols, W.

Smith, and F.P. Wolforth. 1950. Barometric pres-

sure—patterns and spring bird migration. Wilson Bull.

62:5-19.

Brodeur, S., R. Deecarie, D.M. Bird, and M. Fuller.

1996. Complete migration cycle of Golden Eagles

breeding in northern Quebec. Contfor 98:29.3-299.

Brown, L.H. and D. Amadon. 1968. Eagles, hawks, and

falcons of the world. Vol. 2. McGraw-Hill Book Co.,

New York, NY U.S.A.

Craig, J.R. 1981. Bald and Golden Eagle winter popula-

tion surveys. Wildlife Research Report: Part I. Federal

Aid Job Final Report. Colorado Division of Wildlife,

Denver, CO U.S.A.

Dixon, W.J. 1981. BMDP. Statistical Software. Univ. of

California Press, Berkeley, CA U.S.A.

Garcei.on, D.K., M.S. Martell, P.T. Redig, and L.C.

Buoen. 1985. Morphometric, karyotypic, and laparo-

scopic techniques for determining sex in Bald Eagles.

J. Wildl. Manage. 49:595-599.

Gerrard, J.M., D.W.A. Whitfield, P. Gerrard, P.N. Ger-

RARD, AND WJ. Maher. 1978. Migratory movements

and plumage of subadult Saskatchewan Bald Eagles.

Can. Field-Nat. 92:37.5-382.

and P.N. Gerrard. 1982. The spring migration of

Bald Eagles in the vicinity of Saskatoon. Blue Jay 40:

56-60.

Griffin, D.R. 1943. Homing experiments with Herring

Gulls and Common Terns. Bird-banding 14:7-23.

Grubb, T.G., W.W. Bowerman, and P.W. Howey. 1994.

Tracking local and seasonal movements of wintering

Bald Eagles Haliaeelus leucocephalus from Arizona and

Michigan with satellite telemetry. Pages 347-358 mB.-U. Meyburg and R.D. Chancellor [Eds.], Raptor

conservation today. World Working Group on Birds

of Prey. Pica Press, London, U.K.

Harmata, A.R. 1984. Bald Eagles of the San laris Valley,

Colorado; their winter ecology and spring migration.

Ph.D. dissertation, Montana State University, Boze-

man, MT U.S.A.

, J.E. Toepfer, and J.M. Gerrard. 1985. Fall mi-

gration of Bald Eagles produced in northern Sas-

katchewan. Blue Jay 43:56-62.

AND D.W. Stahlecker. 1993. Fidelity of Bald

Eagles to wintering grounds in southern Colorado

and northern New Mexico. /. Field Ornithol. 64:129-

134.

Hinz, T.C. 1974. Seasonal activity, numbers and distri-

bution of Canada Geese {Branta canadensis) in the

lower Yellowstone Valley, Montana. M.S. thesis, Mon-tana State University, Bozeman, MT U.S.A.

Jenkins, M.A., T.P. McEneaney, I.. Hanebury, and J.R

Squires. 1982. Bald Eagle (Ffaliaeetus leucocephalus) es-

sential habitat on and near Bureau of Land Manage-

ment lands in Wyoming. Draft final report—FY 1981

& 1982. Wintering Bald Eagles. U.S. Dept, of Interior,

Fish & Wildl. Service, Denver, CO U.S.A.

Kiesier, G.P., Jr. and R.G. Anthony. 1983. Characteris-

tics of Bald Eagle communal roosts in the Klamath

Basin, Oregon and California.J. Wildl. Manage. 47

1072-1079.

King, J.R. and D.S. Earner. 1963. The relationship of fat

deposition to Zugunruhe. Condor 65:200—223.

Kramer, G. 1952. Experiments on bird orientation. Ibis

94:265-285.

. 1957. Experiments on bird orientation and their

interpretation. Ibis 99:196-227.

Leighton, F.A., J.M. Gerrard, P. Gerrard, D.W.A. Whit-

field, and W.J. Maher. 1979. An aerial census of Bald

Eagles in Saskatchewan./. Wildl. Manage. 43:61-69.

Linc:oln, F.C. 1979. Migration of birds. In S.R. Peterson

and P.A. Anastasi [E.DS.], Fish & Wildlife Service Cir-

cular 1 6. U.S. Dept, of Interior, Washington, DCU.S.A.

Matthews, G.V.T. 1963. The orientation of pigeons as

affected by the learning of landmarks and by the dis-

tance of displacement. Anim. Behav. 11:310—317.

McCleeland, B.R., L.S. Young, D.S. Shea, P.T. Mc-Cleliand, H.L. Ai.len, and E.B. Spettigue. 1982. TheBald Eagle concentration in Glacier National Park,

Montana: origin, growth and variation in numbers.

Living Bird 19:133—15.5.

, L.S. Young, P.T. McClelland, J.G. Crenshaw,

H.I.. Allen, and D.S. Shea. 1994. Migration ecology

of Bald Eagles from autumn concentrations in Glacier

National Park, Montana. Wildl. Monogr. 125.

Meyburg, B-U., D.H. Ellis, C. Meyburg, J.M, Mendel-

son, and W. Scheller. 2001 . Satellite tracking of two


Lesser Spotted Eagles, Aquila pomarina, migrating

from Namibia. Ostrich 72:35-40.

Miner, N.R. 1975. Montana Golden Eagle removal and

translocation project. Pages 155-162 in Proc. of the

Second Great Plains Wildlife Damage Control Work-

shop. U.S. Fish & Wildlife Service, Denver, CO U.S.A.

Newton, I. 1979. Population ecology of raptors. Buteo

Books, Vermillion, SD U.S.A.

Pfnnycuick, C.J. 1975. Mechanics of flight. Pages 1-75 in

D.S. Earner and J.R. Bang [Eds.], Avian biology. Vol.

V. Academic Press, New York, NY U.S.A.

Restani, M., A.R. Harmata, and E.M. Madden. 2000. Nu-

merical and functional responses of migrant Bald Ea-

gles exploiting a seasonally concentrated food source.

Wilson Bull. 102:561-568.

Ryder, R.A. 1965. A checklist of the birds of the Rio

Grande drainage of southern Colorado. Colorado

State Univ. Press, Ft. Collins, CO U.S.A.

Swenson, J.E. 1983. Is the northern interior Bald Eagle

population in North America increasing? Pages 23-

34 in D.M. Bird, Biology and management of Bald

Eagles and Ospreys. Harpell Press, Ste. Anne de Belle-

vue, Quebec, Canada.

Welty, J.C. 1982- The life of birds, 3rd Ed. W.B. Saunders

Co., Philadelphia, PA U.S.A.

Received 21 December 2001; accepted 6 July 2002

J.Raptor Res. 36(4):265-279


DOES NORTHERN GOSHAWK BREEDING OCCUPANCYVARYWITH NEST-STAND CHARACTERISTICS ON THE OLYMPIC

PENINSULA, WASHINGTON?

Sean P. Finn^Biology Department, Boise State University, 1910 University Drive, Boise, ID 83725 US.A.

Daniel E. Varland^Rayonier, 3033 Ingram Street, Hoquiam, WA 98550 US.A.

John M. MarzluffCollege ofForest Resources, University of Washington, Box 352100, Seattle, WA 98195 US.A.

Abstract.—To determine stand-level habitat relationships of Northern Goshawks (Accipiter gentilis) onWashington’s Olympic Peninsula, we surveyed all known historically-occupied sites {N = 30) for occu-

pancy. We measured 45 forest-stand attributes at these sites and found, using stepwise logistic regression,

that goshawks were most likely to occupy historical nest sites with high overstory depth (maximumoverstory height-minimum overstory height) and low shrub cover. Forest managers can manage for

high overstory depth (>25 m) and low shrub cover (<20%) by conducting a single, moderate-level

thinning (leaving 345-445 trees/ha) in young, even-aged 30-35-yr-old stands. Overstory canopy andshrub cover conditions should improve over a 5—10 yr period following thinning. Values for some habitat

features (i.e., percent shrub cover, percent canopy closure, and total snags/ha) in our study were near or

within the range of values reported for Spotted Owls {Strix occidentalis) in young forests on the Olympic

Peninsula. Thus, forest management recommendations described herein may also benefit Spotted Owls.

Key Words: Northern Goshawk, Accipiter gentilis; logistic regression-, overstory depth, shrub cover, Washington-,

wildlife habitat relationships, silviculture, thinning, forestry.

VARIA LA OCUPACION REPRODUCTIVA DEL AZOR CON LAS CARACTERISTICAS DEL SITIO—NIDO EN LA PENINSULA OLYMPIC, WASHINGTON?

Resumen.

—

Para determinar las interrelaciones del habitat a nivel del sitio-nido para el Azor {Accipiter

gentilis) en la peninsula Olympic de Washington, estudiamos todos los sitios ocupados conocidos his-

toricamente {N = 30) . Medimos 45 atributos de los sitios en bosques y encontramos, usando regresion

logistica paso a paso, que estos azores probablemente ocuparon historicamente sitios nido con cubierta

densa (maxima altura de la cubierta-minima altura de la cubierta) y baja cobertura arbustiva. Los

administradores de bosques puedan manejar cubiertas densamente altas (^25 m) y baja cobertura

arbustiva (<20%) llevando un simple, y moderado nivel de entresaca (dejando 345—445 arboles/ha) en

plataformas jovenes, o incluso de edades entre 30-35 ahos. La cubierta del dosel y las condiciones de

la cobertura arbustiva deben mejorar en un periodo de 5-10 ahos despues de la entresaca. Los valores

para algunas caracteristicas de habitat (v.gr. Porcentaje de cobertura arbustiva, porcentaje de cerra-

miento del dosel, y total de tocones/ha) en nuestro estudio estuvieron cerca o dentro del rango de los

valores reportados para Strix occidentalis en bosques jovenes de la peninsula Olympic. De esta manera las

recomendaciones para el manejo de los bosques que se dan aqui, pueden beneficiar ademas a los buhos.


Of critical importance to the success of an or-

ganism is its selection and use of resources. Selec-

^ Current address: USGS, Forest and Rangeland Ecosys-

tem Science Center, Snake River Field Station, 970 LuskStreet, Boise, ID 83706 U.S.A.

^ Corresponding author’s e-mail address: daniel.varland®

rayonier.com

tion among available resources may be especially

important in large mobile organisms that rapidly

move through extensive areas and sample available

resources at a relatively coarse grain (Stern 1998).

Large mobile organisms living in structurally-com-

plex habitats may be particularly responsive to

changing conditions because the various compo-

265

266 Finn et al. VoL. 36, No. 4

nents of their habitat may singly or interactively

affect their preferred breeding sites, thermal en-

vironment, prey abundance and distribution, vul-

nerability to predators, or their competitive status

(Hilden 1965, Patton 1997). The Northern Gos-

hawk {Accipiter gentilis; hereafter known as gos-

hawk) is an excellent example of such an organ-

ism. Goshawks inhabit boreal and temperate

forests within the Holarctic region (Squires and

Reynolds 1997). Because they are highly mobile,

long-lived, and can take a broad assortment of prey

(Squires and Reynolds 1997, Watson et al. 1998),

they are able to select among many different avail-

able habitats for breeding, roosting, foraging, and

other activities.

Much research has focused on goshawk habitat

use and requirements (Block et al. 1994, Squires

and Reynolds 1997), primarily in response to con-

cerns over habitat alteration (DeStefano 1998) and

potential population declines (Crocker-Bedford

1998). Goshawks are described as forest generalists

at large spatial scales, but are a species with nar-

rower habitat requirements at nest sites (Squires

and Reynolds 1997). At the nest-stand scale, re-

search has shown that goshawks select stands with

large-diameter trees and high canopy closure, re-

gardless of forest type or region (DeStefano 1998).

To evaluate relationships between extant habitat

and goshawk site-occupancy, we measured 45 forest

characteristics in nest stands at 30 historical sites

(Table 1); 29 sites were on the Olympic Peninsula

and one was just south of this location (Fig. 1).

Hereafter, because of the proximity of this site to

the peninsula, all sites are referred to as Olympic

Peninsula sites.

Our objectives were to: (1) estimate current oc-

cupancy and breeding rates at all historically oc-

cupied goshawk nest sites on the Olympic Penin-

sula, (2) describe the relationship between

goshawk nest-stand occupancy and nest habitat at-

tributes (see Finn et al. 2002 for descriptions at

larger spatial scales), and (3) offer managementrecommendations based on our findings. We hy-

pothesized that the 30 historical nest sites we iden-

tified for study would still be occupied during our

study if forest conditions at these sites had not

been degraded since they were first discovered. Wereasoned that habitat degradation at nest sites

would result in sites being unoccupied and that

sites we found to be occupied would more closely

resemble forest conditions at historical sites whenthey were used by goshawks.

SruDY Area

The peninsula is composed of a central core of ruggedmountains surrounded by more level, forested lowlands.

Elevation ranges from 0-2420 m, although all known gos-

hawk nests were restricted to elevations ranging from ca.

150-810 m. Mixed coniferous forest is the dominant veg-

etation over most of the peninsula although tree species,

age, and composition vary along a west-east moisture gra-

dient and from natural and anthropogenic disturbances

(Franklin and Dyrness 1988, Agee 1993). Western slopes

are dominated by Sitka spruce {Picea sitchensis)

,

western

hemlock ( Tsuga heterophylla) , and western redcedar(Thu-

ja plicata) whereas the central and eastern portions con-

tain pure or mixed stands of western hemlock and Doug-las-fir (Pseudotsuga menziesii)

,along with western redcedar

and Pacific silver fir {Abies amabilis). Riparian and re-

cently-disturbed areas usually contain stands of red alder

{Alnus rubra), which may also grow in the understory or

in tree gaps on older upland sites. Understory and shrub-

layer densities vary widely and contain western hemlock,

red alder, Pacific rhododendron {Rhododendron macro-

phyllum), sword fern {Polystichum munitum), and salal

( Gaullheria shallon)

.

Vegetation on the Olympic Peninsula is influenced

greatly by the management strategies of the four princi-

pal landowners, resulting in a mixture of forest stands of

varied serai stages. The Olympic National Park (ONP,365 000 ha, Holthausen et al. 1995) does not engage in

commercial timber harvest. Under the Northwest Forest

Plan, the ONP is classified as Congressionally Withdrawn(USDA and USDI 1994). The oiympic National Forest

(ONF, 254 000 ha) is managed under the Northwest For-

est Plan for multiple uses (USDA and USDI 1994) in

which forest management now occurs at low levels in lim-

ited areas. Forest management on lands managed by the

Washington Department of Natural Resources (DNR,164 000 ha) is guided to a significant extent by a Habitat

Conservation Plan (Washington State Department of

Natural Resources 1997). However, the focus on these

lands and on private forest lands (347 000 ha) is on com-mercial timber production and forest management. For-

est cover conditions on the ca. 1.2 million ha of the

Olympic Peninsula may be summarized by the percent

of total area of each ownership class in nesting, roosting

or foraging habitat for the Spotted Owl {Strix occidentalis)

as defined by Holthausen et al. 1995: ONP—46%, ONF= 38%, DNR = 20%, and private/other non-federal =

7%.

MRtJIODS

Occupancy at historical nest sites is an important mea-sure of habitat suitability because goshawks usually exhib-

it high site fidelity (Crocker-Bedford 1990, Woodbridgeand Detrich 1994, Squires and Reynolds 1997). We mea-sured stand attributes at historical nest sites and avoided

measures at random locations to eliminate the inherent

bias of most use-availability studies that statistically test

what is already known; that animals are nonrandomly dis-

tributed in the environment (Cherry 1998, Johnson1999).

Occupancy Surveys. We defined 30 goshawk location

records as historical nest sites after reviewing all sight re-

cords in state and federal databases. All historical nest

December 2002 Goshawk Nest-stand Habitat 267

Table 1. Northern Goshawk survey effort at 30 historical nest sites (170 or 314 ha) on the Olympic Peninsula,

Washington, 1996-98. In 1996, a 170 ha area was surveyed around each site and in 1997-98, a 314 ha area was

surveyed.

Site Name/Number®

1996

No. OF Visits

1997

No. OF Visits

1998

No. of Visits

Sta- Court-

TUS SHIP

Nest-

ling

Fledg-

ling

To-

tal^

Court-

ship

Nest-

ling

Fledg-

ling

To-

tal^

Court-

ship

Nest-

ling

Fledg-

ling

To-

tal’’

Calawah/Sitkum/ 1

2

O 2 2 1 5 2 2 1 5 3 1 4

Raney Creek/29 O 1 2 1 4 1 1 2 1 3 2 6

Dungeoness/16 1 1 1 1 1 3 1 1 2

Burnt Mountain/2 O 3 7 1 11 3 2 1 6 1 1 2

The Hole/30 O 1 6 1 8 3 3 1 7 1 1 2

Donkey Creek/26 O 1 6 1 8 3 2 2 7 1 2 1 4

Snow Creek/ 18 U 2 2 4 3 1 4 1 2 1 4

Morganroth Flat/20 u 1 2 1 4 1 3 1 5 2 2 4

Swede Road/4 u 1 3 1 5 3 1 4 3 1 4

Bear Creek/3 u 2 1 1 4 3 1 4 1 2 1 4

N Fork Solduc/7 o 1 1 2

Mount Zion/ 14 o 1 1 2

Wolf Creek/ 11 o 2 2 4

West Twin River/

1

u 3 1 4

Dosewallips/24 u 3 1 4

Cook Reload/28 u 3 1 4

Wildcat Mountain/5 u 3 1 4

Bear Mountain/ 13 u 2 2 4

Boulder Creek/9 u 3 1 4

Iverson/

6

u 2 2 4

Bowman Creek/ 19 o 2 2 4

Antelope Creek/15 o 2 2 4

Lillian River/ 17 o 1 1 2

Snahapish River/25 u 1 2 1 4

Big Canyon/23 u 2 2 4

Palo Alto/ 10 u 2 2 4

Bingham Creek/27 u 2 2 4

Caraco Creek/8 u 2 2 4

Dry Creek/21 u 1 1 2 4

Minnie Peterson/22 u 2 2 4

“ See Fig. 1 for location by site number.’’ Minimum of four visits required to meet protocol. Where <4 visits shown, occupancy was determined before protocol was met

In 1996, occupancy determination was made early in nesting season by Watson (Watson et al. 1998).

sites: (1) were in the Washington Heritage Database, first

located between 1976-94; (2) were occupied by at least

one goshawk when reported; and (3) contained a large

stick nest at the time of the goshawk sighting. Annualdata on goshawk occupancy were unavailable for all of

these sites, so no historical analyses were possible. Wesurveyed each historical nest site for goshawk occupancy

using standardized aural broadcast surveys (Kennedy andStahlecker 1993, Joy et al. 1994, Finn et al. 2002). Wesurveyed a minimum of a 1 70-ha circle surrounding 10

historical nest sites in 1996 and a 314-ha circle (1 kmradius) surrounding 20 historical nest sites in 1997-98.

The survey area was centered on the most recently used

nest structure or, when no nest structure was found, on

the UTM coordinates on record for that nest site. Be-

cause goshawks are highly mobile and tend to be secre-

tive, we considered a historical nest site to be occupied

if at least one goshawk was visually detected within 1 kmof a nest during >1 survey visit (Finn 2000).

The protocol survey involved 4-1 1 survey vi.sits where

calls were broadcast from each station once during nest-

ing, with 1-2 of these survey visits during the fledgling

stage (Table 1). Call stations were 300 m apart along tran-

sects that were 260 m apart. Call stations on adjacent

transects were offset by 130 m. If occupancy was deter-

mined during a survey visit, protocol surveys were dis-

continued but one additional site visit was made during

the fledgling stage to count the number of young


* JO •

^9*1« ^'2

^ Olympic23^ 24

8 *

30

14

20

,28

17

Olympic

National

Park

26^ 18

3^ ^21

A 722

Nation^29

IS

16

Pacific

Ocean

Nest Survey Years

1996 - 1998

• 1997

^ 1998

* 6

Forest

2S

19

•••*

i ‘i

0 ^3

Figure 1. Location of 30 historical goshawk nest sites (170 or 314 ha) on the Olympic Peninsula, Washington.

Goshawk sites outside Olympic National Park and Olympic National Forest were located on land managed by the

Washington Department of Natural Resources or owned by industrial timber companies. Numbers shown are histor-

ical nest site numbers; these correspond to those identified by site name in Table 1. All historical sites were first

discovered by happenstance, 1976-94. Each site was surveyed for goshawk occupancy in 1996-98, with 10 sites re-

ceiving 3 yr of surveys and 20 receiving 1 yr.


fledged. With one exception, where another research

group checked on nest status (Dungeoness site in 1996;

Table 1), all known nests were checked for signs of oc-

cupancy on 2-6 occasions (dependent on nest condition)

during the nesting season.

Because goshawk occupation of historical sites can vary

over time (DeStefano et al. 1994, Keane and Morrison

1994), we surveyed 10 historical nest sites all three years.

This provided an assessment of among-year site occupan-

cy. Seventy percent of the sites maintained the same oc-

cupancy status among any pairing of years, indicating

that goshawk occupancy was consistent among years sam-

pled (Finn et al. 2002; Table 1). Therefore, we classified

all known historical nest sites on the peninsula as occu-

pied if they were occupied Sil yr (N = 12) or not-occu-

pied if they were not found occupied during any of the

three survey years {N = 18).

Classifying sites as “occupied” or “not-occupied”

based on one year of surveys leaves room for misclassifi-

cation. Sites not occupied during the year of survey mayin fact have been occupied earlier or later when no sur-

veys occurred. To address this problem we set a = 0.10

as the upper limit for significant differences between oc-

cupied and not-occupied sites to counter the possibility

that variances were higher in our not-occupied group of

stands because of misclassification. In addition, the man-agement recommendations we provide focus on the at-

tributes of occupied sites rather than on differences be-

tween occupied and not-occupied sites.

Habitat Analysis. To assess nest-stand habitat we mea-sured vegetation characteristics at 30 historical nest sites.

We defined the nest stand as the homogeneous forest

patch surrounding a goshawk nest and delineated stands

by scribing boundaries along ecotones and topographic

features surrounding the nest after examining 1:12 000orthophotographs, 1:16 000 aerial photographs, and 1:

24 000 topographic maps. Boundaries were ground-truthed in the field. Historical nest stands averaged 51,4

ha in size (range = 9-146 ha). Areas within historical

nest stands where habitat alteration occurred, after gos-

hawk occupancy and before our study, were included in

our measurements of nest-stand characteristics. Thus,

our habitat measurements reflect stand conditions at the

time of our surveys, not conditions when the historical

nest site was originally determined to be occupied by gos-

hawks.

We measured 45 forest characteristics (Appendix 1) in

9—13 0.04-ha, systematically placed, circular plots (x =

10.5 plots/stand, SE = 0.26) in each nest stand using a

modified USFS Region 6 Timber Stand Exam (USDAForest Service 1989) and methods described by Husch et

al. (1972) and Avery and Burkhart (1983). From plot

center, two concentric plots were established: a variable-

radius plot to sample trees >12.7 cm DBH (Diameter

Breast Height, poletimber and sawtimber) and a fixed-

radius plot to sample trees ^12.7 cm DBH (saplings andseedlings)

.

We estimated basal area, total stem density, and stem

and snag density in six size classes (12.8-38.1, 38.2-63.5,

63.6-88.9, 90.0-114.3, 114.4-139.7, and >139.8 cm) fromvariable radius plots (sampled using a 40 basal area factor

prism). We grouped snags into a single size class (^15.2

cm) because of the low number of snags in individual

size classes. We also recorded species, DBH, total height,

crown ratio, crown class, and level of mistletoe infection

for each tree. Quadratic mean diameter at breast height

(QDBH) was calculated as ((S DBH'^)/n)*^ We used a

clinometer to estimate tree heights. Crown ratio, crownclass, and mistletoe abundance were estimated visually

for eacb tree in the variable plot and then averaged for

the plot. A sample of 1-3 trees of each species on eachplot was cored for age and 10-yr radial growth rate. Over-

story and understory canopy characteristics (i.e., oversto-

ry canopy closure, and maximum and minimum oversto-

ry heights) were estimated by averaging four

measurements recorded while facing the cardinal direc-

tions. Overstory and understory canopy closure were e.s-

timated using a moosehorn (Robinson 1947). Overstory

and understory height and depth were the mean of four

ocular estimates of the height of live branching in the

two canopy layers. We used field data to calculate stand

density index (SDI, Reineke 1933) and stem density of

overstory (38.2-150 cm DBH) and understory (2.5-38.1

cm DBH) trees for each nest stand. All variables wereaveraged per plot, then per stand.

Seedling and sapling densities were measured on a

fixed-radius plot where all trees <12.7 cm in diameter

were tallied and grouped by 2.5-cm diameter class. Meanvalues of height, crown ratio, crown class, and mistletoe

infection were calculated for each diameter class. We es-

timated density and height of shrub and herb layers, andcoarse woody debris (CWD) characteristics on eight 1-m^

(Daubenmire 1959), nested plots. Plant association was

assigned to all vegetation plots following Henderson et

al. (1989).

Statistical Analysis. In our study, the number of pre-

dictor variables, 45, exceeded the experimental units, 30

Therefore, we first examined the relative differences be-

tween occupied and not-occupied nest sites for each var-

iable using box-and-whisker plots (Johnson 1999). Weused this approach because simultaneous univariate tests

increase the Type I error rate (Rice 1989) and because

the extensive hypothesis testing inherent in multiple uni-

variate tests is inappropriate for exploratory analyses such

as we undertook (Cherry 1998, Johnson 1999). We eval-

uated the box-and-whisker plots and identified variables

with central tendencies that varied with occupancy. Weselected a subset of variables that: (1) showed differences

in central tendency between occupied and not-occupied

sites, (2) had statistical integrity (approximate normaldistribution, low multicolinearity), (3) had biological in-

tegrity (accuracy of measurement, relevance to gos-

hawks), and (4) forest managers could effectively man-age (i.e., overstory canopy closure can be managed, but

percent slope cannot). The variables chosen were then

evaluated as predictors of goshawk historical nest site oc-

cupancy using stepwise logistic regression models (Hos-

mer and Lemeshow 1989, PROC Logistic, SAS Inst. 1998)

to explain variation in the binomial-response variable

(occupied vs. not-occupied, a < 0.10). We compared a

main-effect model to models that included selected in-

teraction terms to assess their significance.

Results

We surveyed 10 historical sites all 3 yr (1996-98)

and 20 sites during 1 yr (N = 50 annual site-sur-

270 Finn et al. VoL, 36, No. 4

Stem Density Decadence

Figure 2. Habitat characteristics of goshawk nest stands (9—146 ha) at 30 historical nest sites on the Olympic Pen-

insula, Washington. The historical sites associated with these stands were either not-occupied {N = 18, dark boxes)

or occupied {N= 12, white boxes) by goshawks, 1996-98. Boxes depict the median score and 25% and 75% quartiles.

Whiskers represent the 10th and 90th percentiles and black dots represent the 5th and 95th percentiles.

veys; Table 1 ) . We confirmed presence of goshawks

during 20 of these 50 site-surveys (40% occupancy

rate). At the 20 site-surveys where we observed gos-

hawks, we saw birds during >2 survey visits 75% {N= 15) of the time. During the other five site-sur-

veys that revealed occupancy, we observed an adult

goshawk during one visit. In all five cases, the

bird’s behavior suggested it occupied the area (i.e.,

alarm vocalization or site tenacity during the ob-

servation). We determined that 12 of the 30 his-

torical nest sites were occupied (Table 1 ) . All gos-

hawk responses were detected <300 m from a

historical nest site location.

Stand size at historical nest sites was 9-146 ha (x

= 51.4, SE = 6.4). Occupied nest stands were

smaller in size {x = 32.6 ha, SE = 5.5, range =

11.6-69.3) than not-occupied nest stands {x = 63.9

ha, SE = 10.9, range = 8.7—146.2). Historical nest

stands (N = 30) were composed of large {x = 57.3

cm DBH, SE = 2.4; x height = 40.8 m, SE = 1.0),

mature (x= 120-yr-old, SE = 12.5) Douglas-fir and

western hemlock trees, usually in association with

other conifers and occasionally with a few red al-

ders.

Compared to not-occupied nest stands, occupied

nest stands tended to have deeper canopies (oc-

cupied median overstory depth = 28.9 m, not-oc-

cupied median = 21.6 m; Fig. 2) and higher can-

opy closure (occupied median overstory canopy

closure = 77.7%, not-occupied median = 71.3%;

Fig. 2). Occupied goshawk nest stands had morelarge-diameter trees than did not-occupied nest

stands (i.e., occupied overstory stem density me-

dian = 191.9/ha, not-occupied median = 121.5/

ha; Fig. 2). Occupied nest stands generally con-

tained more timber (i.e., occupied SDI median =

2204.8, not-occupied median = 1184.2; Fig. 2) and

had less shrub cover than did not-occupied stands

(occupied median == 15.6%, not-occupied median= 36.9%; Fig. 2).

Overstory canopy closure, overstory canopydepth, overstory stem density, SDI, and percent


Canopy Characteristics Misc.

E 25

3 0

W 2

S 1

K

• 15.0

T *5 12.5

r ^;

510.0

1

tj nz

7.5

5.0

12.5

• £ 0.0

Figure 2. Continued.

Unoccupied

Occupied

shrub cover met our variable selection criteria and

were tested as predictors of goshawk nest stand oc-

cupancy. Two of these, overstory canopy depth andpercent shrub cover, were useful in distinguishing

between occupied and not-occupied nest stands.

We found that the equation logit {occupancy) —

— 2.91 + 0.163 {overstory depth) — 0.063 {percent

shrub cover) significantly described (overstory

depth: Wald — 2.97, P = 0.043; percent shrub

cover: Wald — 4.13, P = 0.039) and was an ad-

equate fit (Hosmer and Lemeshow’s goodness of

fit = 4.087, df = 8, P = 0.850) to the data on

goshawk occupancy of historical stands (Fig. 3).

This model including only main effects fit the data

better than did any main effects plus interaction

models appraised with log-likelihood ratio criteri-

on.

Discussion

Our research indicates that occupancy of gos-

hawk nest stands does vary with nest-stand charac-

teristics. Our results agree with most other studies

that report overstory canopy as an important fea-

ture of goshawk habitat (Squires and Ruggiero

1996, Desimone 1997, McGrath 1997, Patla 1997).

These authors reported on the significance of over-

story canopy closure in the nest stand but we found

stand-wide overstory depth (maximum overstory

height-minimum overstory height) more valuable

in predicting goshawk nest-stand occupancy. Deep,

dense forest canopy {x = 28.7 m, 95% GI = 24.8-

32.6) may provide thermal cover (Newton 1979),

protection from rain, or cover protection from

predators (e.g.. Great Horned Owls {Bubo vir^ni-

anus\, Reynolds et al. 1982, Squires and Reynolds

1997).

On the Olympic Peninsula, occupied nest stands

typically had about 50% the shrub cover of not-

occupied nest stands (Fig. 2). The odds of goshawk

occupancy decreased by 47% for each 10% in-

crease in percent shrub cover (based on the odds

ratio from the logistic regression analysis). Fur-

thermore, productive goshawk nest stands hadabout half the shrub cover of occupied (10.6% vs.

19.0%; Table 2).

Most other goshawk habitat studies have not re-

ported shrub density (Speiser and Bosakowski

1987, Crocker-Bedford and Chaney 1988, Kennedy


Tree Girth Ground Cover

Figure 2. Continued.

Figure 3. The probability (p) of goshawks occupying a

historical nest site on the Olympic Peninsula, Washing-

ton, increases with increasing overstory depth and de-

creasing percent shrub cover at the nest stand scale (9—

146 ha).

1988, Siders and Kennedy 1996, Desimone 1997,

McGrath 1997, Penteriani and Faivre 1997) or have

reported it as non-important in contributing to

goshawk site occupancy (Hayward and Escano

1989, Squires and Ruggiero 1996, Patla 1997).

DeStefano and McCloskey (1997), however, con-

tend that the relative absence of goshawks from the

Oregon Coast Range is due to the dense understo-

ry conditions there, which, in turn, limit prey avail-

ability. Goshawks rarely forage near their nests

(Beier and Drennan 1997), so the lack of shrub

cover we found in nest stands may be unrelated to

prey availability. We did not measure shrub cover

beyond the nest stand scale, however. At landscape

scales (177-ha post-fledging area, 1886-ha homerange), goshawk nest stand occupancy was predict-

ed by a high proportion (60-75%) of late serai for-

est (>70% canopy closure of conifer species with

>10% of the canopy in trees >53 cm DBH) and

reduced landscape heterogeneity (Finn et al.

2002 ).

Our study may have bias because all nest sites

were located opportunistically instead of as a result


Table 2. Nest stand (9-146 ha) habitat characteristics of occupied {N = 12) and productive {N = 8) historical nest

sites of the Northern Goshawk on the Olympic Peninsula, Washington, 1996-98.

Occupieda Productive'^

Variable‘s Mean SE 95% Cl Mean SE 95% Cl

Mean DBH (cm) 58.8 3.7 50.6-67.0 58.2 5.4 45.5-71.0

Quadratic mean DBH (cm) 64.0 4.3 54.5-73.5 63.6 6.3 48.7-78.6

Maximum DBH (cm) 134.2 14.7 102.0-166.4 139.4 21.9 87.7-191.2

Minimum DBH (cm) 17.4 1.1 15.1-19.7 18.0 1.5 14.4-21.6

Mean tree height (m) 43.0 1.7 39.2-46.8 43.1 2.2 37.8-48.3

Crown ratio (index) 5.1 0.2 4.6-5.6 5.0 0.3 4.2-5.7

Crown class (index) 3.1 0.1 3.0-3.2 3.0 0.1 2.9-3.2

Mistletoe (index) 2.5 0.6 1. 2-3.8 1.8 0.6 0.5-3.

1

Radial growth (cm) 1.7 0.3 1.2-2.3 1.9 0.3 1. 1-2.6

Mean tree age (yr) 147.4 22.8 97.2-197.6 128.9 25.4 68.7-189.0

Maximum tree age (yr) 247.6 .33.0 175.1-320.1 229.2 37.0 141.7-316.7

Mean sapling DBH (cm) 5.3 0.7 3.9-6.7 5.1 1.0 2.7-7.4

Mean sapling height (m) 5.7 0.6 4.4-7.0 5.7 0.8 3.8-7.5

Overstory canopy closure (%) 78.4 2.9 72.1-84.7 79.0 4.1 69.3-88.8

Minimum overstory height (m) 18.6 0.9 16.6-20.6 19.9 1.0 17.6-22.2

Maximum overstory height (m) 47.3 2.0 42.9-51.7 47.0 2.7 40.6-53.4

Overstory depth (m) 28.7 1.8 24.8-32.6 27.1 2.3 21.7-32.4

Understory canopy closure (%) 13.7 3.7 5.6-21.8 13.9 5.1 1.8-26.0

Min. understory height (m) 4.6 0.9 2.7-6.5 5.8 1.0 3.2-S.3

Maxi, understory height (m) 16.5 1.1 14.1-18.9 16.6 1.5 13.1-20.2

Understory depth (m) 11.9 0.9 9.9-13.9 10.9 0.7 9.1-12.6

Percent shrub cover (%) 19.0 4.2 9.7-28.3 10.6 2.5 4.8-16.4

Mean shrub height (cm) 41.9 4.7 31.7-52.1 39.9 4.2 29.9-49.9

Percent herb cover (%) 36.5 3.2 29.5-43.5 5.0 4.2 25.1-44.9

Mean herb height (cm) 3.6 0.2 3.1-4.1 3.4 0.2 3.1-3.8

CWD cover (%) 11.0 1.3 8.1-13.9 12.7 1.5 9.0-16.3

CWD height (cm) 42.1 4.8 31.6-52.6 45.0 5.6 31.9-58.2

CWD length (m) 11.0 0.9 9.0-13.0 11.5 1.3 8.3-14.6

CWD DBH (cm) 40.6 3.6 32.7-48.5 41.2 5.1 29.2-53.2

Slope (%) 40.5 5.0 29.5-51.5 42.5 5.7 28.9-56.0

Aspect (degrees) 269.9 26.3 218.4-321.3 294.5 63.5 170.1-58.9

Basal area (m^/ha) 71.4 5.9 58.5-84.3 68.5 5.7 55.0-81.9

Sapling den. (No./ha) 797.3 180.8 399.4-1195.2 831.3 259.3 218.1-1444.6

Small stem density (No./ha) 286.6 41.9 194.4-378.8 297.2 63.8 146.3-448.1

Med. stem density (No./ha) 151.0 22.5 101.6-200.4 146.4 23.4 91.2-201.7

Large stem density (No./ha) 39.1 7.7 22.2-56.0 32.5 8.1 13.3-51.8

Ex.-large stem den. (No./ha) 2.3 1.4 0.0-5.3 2.4 2.0 0.0-7.0

Understory stem den. (No./ha) 1083.9 219.8 600.0-1567.8 1128.5 320.9 369.6-1887.4

Overstory stem den. (No./ha) 192.5 21.9 144.2-240.8 181.3 22.6 127.9-234.8

Live stem density (No./ha) 485.4 47.4 381.0-589.8 488.0 67.9 327.4-648.6

Stand density index 2136.0 223.1 1644.9-2627.1 2107.1 317.6 1355.9-2858.3

Tree species richness (No.) 3.2 0.4 2.2-4.2 3.1 0.5 1.9-4.3

Percent hardwood (%) 1.9 1.2 0.0-4.4 1.2 0.6 0.0-2.7

Snag density (No./ha) 35.8 6.0 22.6-49.0 40.0 6.7 24.2-55.8

Seedling (No./ha) 2031.0 657.8 583.3-3478.7 2671.5 911.8 515.1-4827.9

‘‘12 sites: eight productive (where ^1 young fledged) and four occupied with no productivity.

Eight productive sites.

= See Appendix 1 for descriptions of habitat variables.

274 Finn et ai.. VoL. 36, No. 4

of systematic searches of the full range of goshawk

habitat (Squires and Reynolds 1997, Daw et al.

1998) . Our sample included all of the nests reliably

reported on the Olympic Peninsula over an 18-yr

period, 1976-94. Thus, though our sample is small,

it IS likely adequate to represent goshawk habitat

use by goshawks on the Olympic Peninsula. Fur-

thermore, Daw et al. (1998) compared goshawk

nest stand habitat in stands found opportunistically

with those found by systematic searches in Oregon

and found no differences in two key habitat vari-

ables, large tree density and canopy cover. Their

sample of opportunistically-located nests included

nests found by individuals searching for goshawk

nests with a preconceived notion of goshawk hab-

itat preferences (i.e., searching likely habitat).

Nests in our study, however, were found by individ-

uals whose reasons for being in the held varied

greatly (i.e., hikers, Marbled Murrelet {Brachyram-

phus marmoratus) surveyors, foresters conducting

timber cruises) and who, in nearly all cases, were

focused on activities other than hnding goshawk

nests. The Daw et al. (1998) study provides empir-

ical evidence that the method we employed for

identifying historic nest sites was adequate.

While we provide useful information on the

characteristics distinguishing between occupied

versus not-occupied nest stands, we recognize that

site occupancy is not necessarily indicative of qual-

ity habitat (Van Horne 1983, Vickery et al. 1992).

We believe our occupancy surveys are good indi-

cators of habitat quality for goshawks because, in

our study, nest-stand occupancy and reproduction

were closely correlated (Finn 2000, Finn et al.

2002) . Young successfully fledged from eight of 1

2

occupied sites. Moreover, only one of the 10 sites

we surveyed every year was consistently occupied,

but never produced fledglings.

Small-scale (e.g., nest tree, nest vicinity) habitat

influences on occupancy of goshawk nest stands

were not identihed in our study (Finn 2000). Thus,

forest managers should focus on stand scale (this

paper) and landscape scale (Finn et al. 2002) hab-

itat management for goshawks.

Management Impi.igaiions

Goshawk nest stand size in our study averaged

32.6 ha in occupied historical sites and 63.9 ha in

not-occupied historical sites, which is within the

range of 10—100 ha reported by Squires and Reyn-

olds (1997) for goshawk nest stands across North

America. We recommend that managers who seek

to address nest stand level habitat needs tailor

stand size after the ranges reported here.

Our research indicates that goshawk nest-stand

habitat may be provided on the Olympic Peninsula

by managing stands to create deep overstory can-

opies and low shrub cover (Table 2, Figs. 2 and 3).

Long et al. (1983) and Bailey (1996) report that

large crowns can be created in dominant and co-

dominant trees by thinning stands at 20-50 yr of

age. Thinning reduces crown competition, thereby

enhancing crown development and tree diameter

growth. Thinning, however, allows more light to

reach the forest floor which also promotes under-

story growth (Hayes et al. 1997, Thysell and Carey

2000). Hayes et al. (1997) indicated that thinning

to moderate densities facilitates crown develop-

ment but limits development of understory be-

cause the canopy closes rapidly.

To accelerate the development of deep overstory

canopies in young even-aged stands, we recom-

mend that a single moderate-level thinning take

place in stands 30-35 yr of age. On the Olympic

Peninsula and elsewhere in western Washington

and Oregon, moderate-level thinning would result

in retention of 345—445 trees/ha where heavy thin-

ning would result in retention of 148—247 trees/ha

(L. Raynes pers. comm.).

To promote deep overstory canopies at the onset

of stand initiation, planting a mixture of shade tol-

erant (i.e., western hemlock) and intolerant (i.e.,

Douglas-fir) tree species at 3-4 m spacing is rec-

ommended (ca. 1000 trees/ha, L. Raynes pers.

comm.). Spacing trees farther apart will reduce

crown competition and may result in excessive can-

opy depth (L. Raynes pers. comm.), therein cre-

ating inadequate flight space for goshawks. A sin-

gle, moderate-level thinning of the trees remaining

in the stand (there will be some mortality) at 30-

35-yr-old across the range of diameter classes, as

opposed to thinning a specific diameter class,

would promote deeper forest canopies as the stand

develops; this is because more growing space is

available, particularly for the larger trees (L. Ray-

nes pers. comm.).

Once thinning has occurred, overstory canopy

development and a concomitant reduction in

shrub cover would occur over a 5-10 yr period.

After this, stands would likely be suitable for gos-

hawk nesting for as long as they were retained.

Mean tree age of occupied nest stands in our study

was 147 yr (A = 12, SD = 71.3, range - 51-275).


The four youngest occupied stands were 50-70-yr-

old while the four oldest were 200-275-yr-old.

We suggest that it is not stand age per se that is

important to goshawk nesting, instead it is the hab-

itat elements associated with older stands (this

study: deep overstory canopy, low shrub cover,

Squires and Reynolds 1997, DeStefano 1998: large

trees with high canopy closure). The extent to

which these features can be created in younger-

aged stands will make forest management for gos-

hawks more economically practicable. Other silvi-

cultural prescriptions may work as well as those wesuggest or may be more appropriate, depending

on site conditions. Currently, most stands on the

Olympic Peninsula are managed on a 40-50 yr ro-

tation (L. Raynes pers. comm.), due primarily to a

re-tooling of local sawmills to handle smaller-di-

ameter logs.

The importance of old forest attributes to the

Northern Spotted Owl, which also inhabits western

Washington forests and is sensitive to habitat loss,

is well known (Gutierrez et al. 1995, Horton 1996,

Irwin et al. 2000) . Goshawks, however, use a broad-

er range of forest structural stages than do North-

ern Spotted Owls (DeStefano 1998). We found gos-

hawks nesting in stands as young as 51 yr, andBosakowski et al. (1999) report on goshawks nest-

ing in 40-54-yr-old managed stands in western

Washington.

In research on Northern Spotted Owl use of

young forest habitat on the Olympic Peninsula,

Buchanan et al. (1999) report values for some hab-

itat features important to Northern Spotted Owls

(i.e., total snags/ha, percent shrub cover, percent

canopy closure, and coarse woody debris cover)

that are near or within the range of values wefound for these same features for goshawks (Table

2) . Thus, forest management as described herein

may also benefit Northern Spotted Owls.

Acknowledgments

We want to thank those from private companies andpublic agencies that offered their assistance. The Wash-ington Department of Natural Resources, Rayonier, Port

Blakely Tree Farms, Champion Pacific, and the University

of Washington provided funding and logistical support.

Additional support, equipment, and in-kind aid was pro-

vided by Weyerhaeuser, the Washington Department of

Fish and Wildlife, Olympic National Park, and OlympicNational Forest. We thank R. Meier, L. Raynes, S. Katzer,

N. Wilkins, T. McBride, J. Eskow, D. Runde, L. Hicks, S.

Horton, P. Harrison, D. Hays, S. Desimone, E. Seaman,S Lemioux, and L. Young for their helpful input. Tech-

nical and analytical advice was provided with enthusiasm

by L. Bond, M. Cowing, S. Gossett, B. Lehman, J. Munger,S. Novak, K. Steenhof, and T. Zarriello. Special thanks to

D. Yonkin for his outstanding help in the field, his ded-

ication to the project, and his spirit. Superior assistance

in the field was provided by B. Griffith, H. Tall, K. Bees-

ley, B. Davies, T. Bloxton, J. Delap, J. Swingle, J. Wagen-knecht, and L. Vandernoot. Thanks also to M. Fuller, S

Knick, J. Munger, K. Titus, C. Crocker-Bedford, R. Man-nan, and M. Restani who reviewed and greatly improvedthis manuscript.

Literature Cited

Agee, J.K. 1993. Fire ecology of Pacific northwest forests.

Island Press, Washington, DC U.S.A.

Avery, T.E. and H.E. Burkhart. 1983. Forest measure-

ments. McGraw-Hill, New York, NYU.S.A.

Baiity, J.D. 1996. Effects of stand density reduction onstructural development in western Oregon Douglas-

fir forests—a reconstruction study. Ph.D. dissertation,

Oregon State University, Corvallis, OR U.S.A.

Beier, P. and J.E. Drennan. 1997. Forest structure and

prey abundance in foraging areas of Northern Gos-

hawks. Ecol. Applic. 7:564-571.

Block, W.M., M.L. Morrison, and M.H. Reiser (Eds )

1994. The Northern Goshawk: ecology and manage-

ment. Stud. Avian Biol. 16.

Bosakowski, T, B. McCullough, F.J. Lapsansky, andM.E. Vaughn. 1999. Northern Goshawks nesting on a

private industrial forest in western Washington./. Rap-

tor Res. 33:240-244.

Buchanan, J.B., J.C. Lewis, D.J. Pierce, E.D. Forsman,

and B.L, Biswell. 1999. Characteristics of young for-

ests used by Spotted Owls on the western Olympic

Peninsula. Northivest Sci. 73:255-263.

Cherry, S. 1998. Statistical tests in publications of the

Wildlife Society. Wildl. Soc. Bull. 26:947-953.

Crocker-Bedford, D.C. 1990. Goshawk reproduction

and forest management. Wildl. Soc. Bull. 18:262—269

. 1998. The value of demographic and habitat

studies in determining the status of Northern Gos-

hawks (Accipiler gentilis atricapillus) with special refer-

ence to Crocker-Bedford (1990) and Kennedy (1997)

J. Raptor Res. 32:329-336.

AND B. Chaney. 1988. Characteristics of goshawk

nest stands. Pages 210—216 in R.L. Glinski, B. Giron

Pendleton, M.B. Moss, M.N. LeFrank, Jr., B.A. Millsap,

and S.W. Hoffman [Eds.], Southwest raptor manage-

ment symposium and workshop. Natl. Wildl. Fed.,

Washington, DC U.S.A.

Daubenmire, R.F. 1959. A canopy-coverage method of

vegetational analysis. Northwest Sci. 33:43-64.

Daw, S.K., S. DeStefano, and R.J. Steidl. 1998. Does sur-

vey method bias the description of Northern Goshawknest-site structure? J. Wildl. Manage. 62:1379-1384.

Desimone, S.M. 1997. Occupancy rates and habitat rela-

tionships of Northern Goshawks in historic nesting

areas in Oregon. MS thesis, Oregon State University,

Corvallis, OR U.S.A.


DeStefano, S. 1998. Determining the status of Northern

Goshawks in the west: is our conceptual model cor-

rect? J. Raptor Res. 32:342-348.

, S.K. Daw, S.M. Desimone, and E.C. Meslow.

1994. Density and productivity of Northern Goshawks:

implications for monitoring and management. Stud.

Avian Biol. 16:88—91.

AND J. McCloskey. 1997. Does vegetation struc-

ture limit the distribution of Northern Goshawks in

the Oregon coast ranges? J. Raptor Res. 31:34—39.

Finn, S.P. 2000. Multi-scale habitat influences on North-

ern Goshawk occupancy and reproduction on Wash-

ington’s Olympic Peninsula. M.S. thesis, Boise State

University, Boise, ID U.S.A.

, J.M. Marzluff, and D.E. Varland. 2002. Effects

of landscape and local habitat attributes on Northern

Goshawk site occupancy in western Washington. For.

Sci. 48:427-436.

Franklin, J.F. and C.T. Dyrness. 1988. Natural vegetation

of Oregon and Washington. Oregon State Univ. Press,

Corvallis, OR U.S.A.

Gutierrez, R.J., A.B. Franklin, and W.S. LaHaye. 1995.

Spotted Owl (Strix occidentalis) . In A. Poole and F. Gill

[Eds.], The birds of North America, No. 179. The

Academy of Natural Sciences, Philadelphia, PA and

The American Ornithologists’ Union, Washington,

DC U.S.A.

Hayes, J.P., S.S. Chan, W.H. Emmingham, J.C. Tappeiner,

L.D. Kellogg, and J.D. Bailey, 1997. Wildlife re-

sponse to thinning young forests in the Pacific North-

west. /. For. 95:28-33.

Hayward, G.D. and R.E. Escano. 1989. Goshawk nest-site

characteristics in western Montana and northern Ida-

ho. Gowrfor 91:476-479.

Henderson, J.A., D.H. Peter, R.D. Lesher, and D.C.

Shaw. 1989. Forested plant associations of the Olym-

pic National Forest. U.S. For. Serv. Gen. Tech. Rep.

RG-ECOL-TP 001-88, Portland, OR U.S.A.

Hidden, O. 1965. Habitat selection in birds. Ann. Zool.

Fenn. 2:53—75.

Hoi.thausen, R.S., M.G. Raphael, K.S. McKelvey, E.D.

Forsman, E.E. Siarkey, and D.E. Seaman. 1995. Thecontribution of federal and non-federal habitat to

persistence of the northern Spotted Owl on the Olym-

pic Peninsula, Washington: report of the reanalysis

team. U.S. For. Serv. Gen. Tech. Rep. PNW-GTR-352,

Portland, OR U.S.A.

Horton, S.P. 1996. Spotted Owls in managed forests of

western Oregon and Washington. Pages 215-231 in

D.M. Bird, D.E. Varland, andJ.J.

Negro [Eds.], Rap-

tors in human landscapes: adaptations to built and

cultivated environments. Academic Press Ltd., Lon-

don, U.K.

Hosmer, D.W. and S. Lemeshow. 1989. Applied logistic

regression. John Wiley and Sons, New York, NYU.S.A.

Husch, B., C.I. Miller, and T.W. Beers. 1972. Forest

mensuration, 2nd Ed. The Ronald Press Company,

New York, NY U.S.A.

Irwin, L.L., D.F. Rock, and G.P. Miller. 2000. Stand

structures used by northern Spotted Owls in managedforests, y. Raptor Res. 34:175-186.

Johnson, D.H. 1999. The insignificance of statistical sig-

nificance testing./. Wildl. Manage. 63:763-772.

Joy, S.M., R.T. Reynolds, and D.G. Leslie. 1994. North-

ern Goshawk broadcast surveys: hawk response vari-

ables and survey cost. Avian Biol. 16:24-30.

Keane, JJ- AND M.L. Morrison. 1994. Northern Goshawkecology: effects of scale and levels of biological orga-

nization. Stud. Avian Biol. 16:3-11.

Kennedy, P.L, 1988. Habitat characteristics of Cooper’s

Hawks and Northern Goshawks nesting in New Mex-

ico. Pages 218-227 in R.L, Glinski, B. Giron Pendle-

ton, M.B. Moss, M.N. LeFrank, Jr., B.A. Millsap, and

S.W. Hoffman [Eds.], Southwest raptor managementsymposium and workshop. Natl. Wildl. Fed., Washing-

ton, DC U.S.A.

and D.W. Stahlecker. 1993. Responsiveness of

nesting Northern Goshawks to taped broadcasts of

three conspecific calls. /. Wildl. Manage. 57:2249-2257.

Long, J.N., J.B. McCarter, and S.B. Jack. 1983. A mod-ified density diagram for coastal Douglas-flr. West. JAppl. For. 3:88-89.

McGrath, M.T. 1997. Northern Goshawk habitat analysis

in managed forest landscapes. M.S. thesis, Oregon

State University, Corvallis, OR U.S.A.

Newton, I. 1979. Population ecology of raptors. Buteo

Books, Vermillion, SD U.S.A.

Oliver, C. D. and B. C. Larson. 1990. Forest stand dy-

namics. McGraw-Hill, New York, NY U.S.A.

Patla, S.M. 1997. Nesting ecology and habitat of the

Northern Goshawk in undisturbed and timber harvest

areas on the Targhee National Forest, Greater Yellow-

stone Ecosystem. M.S. thesis, Idaho State University,

Idaho Falls, ID U.S.A.

Patton, D.R. 1997. Wildlife habitat relationships in for-

ested ecosystems, Revised Ed. Timber Press, Portland,

OR U.S.A.

Penteriani, V. AND B. Faivre. 1997. Breeding density and

nest-site selection in a goshawk Accipiter gentilis popu-

lation of the Central Apennines (Abruzzo, Italy). Bird

Stud. 44:136-145.

Reineke, L.H. 1933. Perfecting a stand-density index for

even aged forests. J. Agric. Res. 46:627-637.

Reynolds, R.T., E.C. Meslow, and H.M. Wight. 1982

Nesting habitat of coexisting accipiters in Oregon./

Wildl. Manage. 46:124-138.

Rice, W.R. 1989. Analyzing tables of statistical tests. Evo-

lution 43:223-225.

Robinson, M.W. 1947. An instrument to measure forest

crown cover. For. Chron. 23:222-225.

SAS Institute, Inc. 1998. SAS/STAT user’s guide. Re-

lease 6.03. SAS Inst., Cary, NC U.S.A.

Siders, M.S. and P.L. Kennedy. 1996. Forest structural

Goshawk Nest-stand Habu a i 277December 2002

characteristics of accipiter nesting habitat: is there an

allometric relationship? Conrfor 98:123-1 32-

Spf.tser, R. and T, Bosakowski. 1987. Nest site selection

by Northern Goshawks in northern New Jersey and

southeastern New York. Condor 89:387-394.

Squires, J.R. and L.F. Ruggiero. 1996. Nest-site prefer-

ence of Northern Goshawks in south-central Wyo-

ming. /. Wildl. Manage. 60:170-177.

AND R.T. Rit'VNOl.DS. 1997. Northern Goshawk {Ac-

cipiter gentilis) . In A.. Poole and F. Gill [Ens.], The birds

of North America, No. 298. The Academy of Natural

Sciences, Philadelphia, PA and The American Orni-

thologists’ Union, Washington, DC U.S.A.

Stern, S.J. 1998. Field studies of large mobile organisms:

scale, movement, and habitat utilization. Pages 289-

307 in D.L. Peterson and V.T. Parker [Eds.], Ecolog-

ical scale: theory and applications. Columbia Univ.

Press, New York, NY U.S.A.

Thvneix, D.R. and A.B. Carey. 2000. Effects of forest

management on understory and overstory vegetation:

a retrospective study. U.S. For. Serv. Gen. Tech. Rep.

PNW-488, Olympia, WA U.S.A.

USDA Forest Service. 1989. Stand exam program. Field

procedures guide. U.S. For. Serv. Gen. Tech. Rep., Pa-

cific Northwest Region, Portland, OR U.S.A.

USDA Forest Servk:e and USDl Bureau of Land Man-agement. 1 994. Record of decision for amcndmcnlsto Forest Service and Bureau cjf Land Managementplanning documents within the range of the northern

Spotted Owl. Standards and guidelines for manage-

ment of habitat for late-successional and old-growth

forest related species within the range of the northern

Spotted Owl. Washington, DC U.S.A.

Van Horne, B. 1983. Density as a misleading indicator

of habitat quality. /. Wildl. Manage. 47:893-901.

Vickery, P.D., M.T. Hunter, Jr., and J.V. Wells. 1992 Is

density an indicator of breeding success? Auk 109‘

706-710.

Washincd'on Stale Department of Na'ilral Resources

1997. Final habitat conservation plan. Unpubl. Rep.,

Olympia, WA U.S.A.

Watson, J.W., D.W. Hays, S.P. Finn, and P. Meeiian-Mar-

TiN. 1998. Prey of breeding Northern Goshawks mWashington, y. Raptor Res. 32:297-305.

WOODBRIDtiE, B. AND PJ Detrich. 1994. Territory occu-

pancy and habitat patch size of Northern Goshawks

in the southern Cascades of California. Stud. Avian

Biol. 16:83-87.


Associate Editor: Marco Restani


!U

•1—

•

Co

OJ

cn

Va

1r£3C/>

oOc1)

.rl

o

uCoc«

OCO

t3Ds.^

sc«

dVB

c

>

-D

4=

m;-N

GO

CC4H

OJ

T)

03ddlA

VX.<JdOo,a

GObco^

S ci

’OhSJ^05

doc/3

OJ

Bd pS -S

3 ^d"

c;

kJ^ S> 32

bed

d!-H ^;xj

"3 2^ 9"

^ S

wuzgu

gH

gwQ

do

Xddobe

ot+H

1>SO

ddXd

Id

so

CM

a.

J3udK

d

V

o

o

cd

fl

QJ

CMi>CTi

o;

-15uC/J

X

<v

*cr

c/3

OJ

C;-N

VCL

XSQJ

bJDciuOJ

^

lO

d

<D U'at^BdA

'

‘t! s

ddd

+

ffi

PQ

QW

..^<3

3 3Bbe OJ

cj PQV A nL

Vd Sd ;hu

;h

VVsd3

0300031-H

<1

QCO

L

he_d*-2

C5

(Uc/3

<u5-h

CLc;uc/3

«uc/:

c/3

S'c/5

ao

u>

V A

a

uV•w<u

a•

73.tJ AA HJ03 s

dd aj (3

.Q

Q

O >d dd<J <u

c ^‘C u0 ^Xi CL

dAdo

'Sd

030003

QCO

D

GO

C/5

o;u

C

X5CL)

Lh

:3C/3

OJ

OJ q

1 rOJ o2 J3

73dd y3

hed

II •§

b ^X ^H 73

o a

oXCmOdo

OPhOo ^;.H

d3 's^

d —d dP G•M MA dM ^Al Q^ Sd ^

^ II

g £

O •! 73

O CDShU oD dD O]3 d

X OJ

‘M aj M «g -O d o-d d ^

Mr9"dus-T

DMo

MDCd

73DhedD

IqCJ

LC•4-3

OJ

b/D

<uLh

0Xw

OJ qr! qU(^J

c/5

\ sc/) qOJ

s.SM [/3

GO -CJ

1‘'3

L ^^ d

utuMO

obedMaj

AD73

'H.

73<u

X•

tL

qOJ-4-J

OJ

aqXau

CM

I

klO

CM

aocBi/5

OJOJ

b

J.H

uDO

U00

CM

KPdQddo

KPQ

&KPQ

QddV

dMTjd

§

K E |dPQ eq OJ

Q Q ^ada

D13M

dd

.... 13Xd

dMd

oMU

Ad

X13

73d

ClAs£

”75

S5WJ

73

go??

OJ

boqOJ

'Hh

t3DXXdDMDaqXa

«

d

aCM £

^ ^ =1

^ c4n M ^° a dh o M^ CmD be

ac^ 1—

(

OJ Dd 13 d:

03

doAdX&

uVD

d_d

indu

In13

Oh

73OJ

hodd13

m11

(X

sfl

OJ dCld

Md d 1Cl Cl dd d e

d73_d

M Sh

13

ddG

.oMddd

13

a ^B B t .

X XM M q

Jx X X3 3

ddM

BdM

Bd HHSh 1h 3

PQ P P P g: u 13 U 13 13 B P CJ

P Q Q P U 0 0 0 dIH

dHH 3 P 0

DOMOJd

o

O S

&oDhe

73

ap<

13

bodD13MMddD

X

1)Q

8 bcB d

a "S-

a

"

.a dX dd D

'H,CmOMo-M

d .

13 Tj^ da 9B A

X'dP3

ho_d

"DhdA

dd13

d_o

13

D

d_d

XChdu

^ D T3A Cl VB T3

G a 6a be-B5 dc« B 13

^ CmCm Od d M

a .2 ddCO S

M13

&H

7313

bedo

do1^

U13M

d_d

3hdu

731)

daoAodctMI

o

Do4MIZl

Ch13

>O

daa

X•M^'dP3

o.MAin13

>o

03

do

rO

u13Sh

dd1—

(

73Ch

d13

"a3+H

oMDd .

13 TO^ d

d

13

Cl

73obodii13

d0

•

UOJLh

• 1^

731 I

qq

•^73Uid1)

o dod.< 13

ga.

Xbo

13

d ch+H QJ T3c/5 CL UB ^ dal 9c bo -j3'd d -

£ ^B 'd

tH d« O^ qo a

o

M1)

Cl

7313

bed113

'a

doX13

uM

ddX1du

73DMd

VtHCmO

>•-M0MA113

73dd

ada'3

S

dDX3+H

735h

O

13

73

gXd

5 °

• SP

d3

S-.doMAMQJ

73dd

AD~Sl

adA

Cl00 A

d Ba o

o da.CL ijj

a ,£p M ^Cl'B X ^ "On Lm qj

o .

d1o-d1)AOo

OJ OJ V OJ CJbiD be be bo bo boq q q q q qu Sm u u S-N

OJ OJ V Ur OJ OJ OJ> > > U > > >q q q 0 q q qL( Lh u X

OJc/5

u u3 3 iS 3 33 3 3 0 3 3 3u u u 0 u u u0 O 0 s 0 0 0

g’Dh

13dddcrA

13Md

d

aoddo

ll

oMAD13d

13be

'd13

I3MMOMA13

dO

ada'd

13

•£P’S13

d-,dowC/!

UOJ>o

adadH

ClOJX>-uOc/5

i-H

OJ

>o

13Md

kMClodd13

d^MoMAu(U

T3dL

Id

'd13

UO.MAuOJ

73dd

da'a

X'C13

d^1oMAU13

73dd

ada'xd

Cl13

Xd^MoMA!h13

73dL

1ddOd13dSh

XAMdddMdPI


T3!U

g

oU

s<uaGh<1

wu2;

swPh

2gH2EwQ

w

03^ GO^ CO

G3

O25uir>

K

OJ

2<!

Og'op<

Ph

-GO03

ooSut/3

Ph

rt

Ou •

<u

Ph

22OJ

"d

oo?OJinUCC

ou

5"3

_o ^ _g ^ g

m in in m ^<L) flj O <U O'g^'g.’g.'Gh'T

s a a a ^cd cd 'rt^ ^ Q

CT CÎ CN CM na a a a i1111

1—1 1—

<

QO 00 00 00^ 4-1 Mh 'Go o o o ^d d d d

O rt O! rOQJ u

'adOJ

beoShocu

22

4

"022

2Obe ÔJ oo Ô l^-(

d O+J D22 ^be Po d22 02

d S

s

in

43O'd

0in O•E ^rG

3J02 «

K ™r^T- Ot3 o

I^ 03(U oin

5 do Ô m

”3 "o4-1 rGO c*^

22°

P P3

r2 Qd Pd d<u 02

bed

Ti02

d

§t3dd

ddd

Gh ^"d02

beda

o

r5 Waod^

KOCM

0302

hed213

CMr'03

d

02

rPuin

Pffi

v:

5/2I/}

T3

r|—

I

V

I'B

PQ

&U r-b

dg ^G< G<

P<

OP *

a ÔJ Q

VN U55 ,0

(3J ^S-! ^

^ Uiqj OJa £X

OJ Vd

rP OSP ^02 12

P

wHc/2

hJ

§.i'rt <r>

OJ U2/5 ^d

-KP

.2 tUin IdP MU g•d £

c/2

P d

00CO

I

j>

CM

CMQ+

XP3

Q

^ u

CM

-r I

d ^G CMIh Sw.r-

ct

o QP- n

KP5Q

1T3

00CD

I

CM

00CO

CO

p

pPQ

Pa02

rP. O

CP

p

P00

“*”

GO cO

^PGO 4-OD'-' mP

Q n

a02-1-)

C/5

O

• rHt/:

dut2

GXUPP+

Pup+

;

p

'

02-I—

>

C/}

o

‘in

dut3

GpuppbePo

030003J-p

<1

pc/2

p

mT2Pd

do12

B12

P0312

'Gd2>

o03 0303 00^ 03

p^

o —

:

^ dci ^p ^

d g2 </2

c5 ;-

12 P> PP 02

O P

ppd

d1212

4<

12

dP

rB"

P12

d

m V mP P PP r^ G

12

p12

P

p 7! ^

pdSh

P

GOPUP

Prt XP SgPpUP •

'

' u.a > .a

^ 22 â|'ad

'

d udc/^ O§K

2 S 212 p g

c4—

I

C/5

ou

0uc/5

OJV5C/5

T3

OJ4—1

cu

1p

J>CM1-M

^ §s ra *-<-* —,

<Xi 5/5

3 ^d o^ d^ p12 2u O12 ^"Io

CM

cn a W o PII

ÎI ‘a ^

UO

Xp«opQop

" p. P Xp p p

^ u up p

I

CM.CM

X. ^P 00 £p GO £

O C^

C-^ CMGO V1-H CD r—

I

rH £ P124—

>

CA P

ddou

u12

12 â .2

a ^pi

V5

OJ

boG’CQJ

-Cl4—*

OJ

ox!dd o12

d p12

r. c/5

o J8(j dd u

P -tJC oG dO HJ

cti1/^

Cd da -a ph-dC/2

12Sr

duUd

mOPOum12

U ‘uH 12p

in

P-rO dd gPU P

12

bed’p

ubed

0 12

bed

12

bed 1 a a a a a a a a

'pc/5

'pc/5 a

aa

12Srd

u12

a

OJ5-h

refH

Sr12

a12P

Sr12

a

POJ-MOJ

c/5

C/3

.-H C/5

P • rH

^Po

C/3

’POh

C/5• rHPa

c/5• rHPOh

c/5

*PCu

c/5

'p

Oh

c/5

‘p

Oh

c/5pOh

d• rHPd

_d

pd

c/5•^POh u

r5

PTin X

PcrC/5 r5

d-H

rSa re

Oh S §Sr

PSr

P S4—1

re

Cl

PrS

3u0

a3u0

a3u0

P12r-i

CZ)

3u0

_g

ua0u

P PO Op P

Pop

pq

oppq

opCQ

oppq

oppq

oppq

op1)

.ap12

.ap

pq

opTally Tallv

j d• rH4—)c/5

P3u0 Key

au

CM1—

H

AC/5

atu4-^

B''Kf212P

12-kJin

12>P

CZ)

PUP

.-B’'in

d12P

XPPP

r-. ^

JdosS-o S' .S'

&ai sa o

G3

a

a^ 02

12

in

d12

P d12P

12-uin

12

.ap

in

0^ t'

^ 2d ^

12

C/3

inSr

d 02be S pSr HI dd X pP P D

XPPo

d-• rHC/5

dOJ

OJ

c/3

;-H

Owc/5

OJ

6

p

c/3

d12

Pbed

• rH

'Pd

CZ)

d12

pbed

* r^

P12

12

C/3

PPP

Id d PhH O

ic/!

.bn OJ —

da;

T3

du â;

^ d

^ 12 u ad 12 Sr Hd p 12 GIZ H P Cd

v.p

do

• rH4—1

d*0

be ^d d

- ap pd pd dP P

tu

.SP‘5

re

1)u

OJudre

C/l

Go;

X!

6OJ

cc c4_(

-1 Se a

ore

CJ

biD;-4

re

zwQ

CO ^Q Q

" W^ a;G p

/. Raptor Res. 36(4):280-286


SUBORDINATE MALES SIRE OFESPRING IN MADAGASCAREISH-EAGLE {HALIAEETUS VOCIFEROIDES) POLYANDROUS

BREEDING GROUPS

Ruth E. Tingay*School of Geography, University of Nottingham, Nottingham, NG7 2RD ILK.

and the Peregrine Fund, 5668 Flying Hawk Lane, Boise, ID 83709 U.S.A.

Meianie Culver, Eric M. Haiuerman, and James D. FraserDepartment ofFisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University,

Blacksburg, VA 24061 U.S.A.

Richard T. WatsonThe Peregrine Fund, 5668 Flying Hawk Lane, Boise, ID 83709 U.S.A.

Abstract.—The island endemic Madagascar Fish-Eagle (Haliaeetus vociferoides) is one of the most en-

dangered birds of prey. Certain populations in west-central Madagascar sometimes exhibit a third, and

sometimes a fourth, adult involved in breeding activities at a nest. We applied DNA fingerprinting to

assess relatedness among 17 individuals at four nests. In all nests with young, a subordinate rather than

the dominant male sired the offspring. Within-nest relatedness comparisons showed that some dominant

males had an apparent hrst-order relationship with the female. Between-nest relatedness comparisons

showed that some adults had an apparent hrst-order relative at another nest in the study area. Findings

that subordinate males contribute to breeding, and that adults in an area may be related, may require

conservation measures such as translocation to assure the species’ survival.

Keywords: Madagascar Fish-Eagle, Haliaeetus vociferoides; DNA fingerprinting, mating system; nest helper,

polyandry.

MACHOS subordinados engendran descendencia en grupos de reproduccion po-

LIAnDRICA en AGUIIAS PESCADORAS DE MADAGASCAR {HALIAEETUS VOCIFEROIDES)

Resumen.—El aguila pescadora endemica de la isla de Madagascar {Haliaeetus vociferoides) es una de las

aves rapaces mas amenazadas de extincion. Algunas poblaciones en el occidente-centro de Madagascar

exhiben algunas veces un tercero y a veces un cuarto adulto involucrado en las actividades reproductivas

en un solo nido, Aplicamos un analisis de ADN para evaluar el parentesco entre 17 individuos de cuatro

nidos. En todos los nidos con juveniles, un macho subordinado mas que el dominante engendro la

prole. Las comparaciones de parentesco dentro de los nidos mostro que algunos machos dominantes

tenian aparentemente una relacion de primer orden con la hembra. Las comparaciones entre nidos

mostraron que algunos adultos tuvieron un pariente de primer orden en otro nido dentro del area de

estudio. El hallazgo de que los machos subordinados contribuyen a la reproduccion, y que los adultos

en un area pueden estar relacionados entre si, pueden hacer necesarias medidas de conservacion tales

como traslados para asegurar la supcrvivencia de la especie.


The island endemic Madagascar Fish-Eagle {Hal-

laeetus vociferoides) is considered critically endan-

'' These two authors contributed equally to this manu-

script.

' Present address of corresponding author: Wildlife and

Fisheries Science, University of Arizona, Tucson, AZ85721 U.S.A.; e-mail address: [email protected]

gered (Collar et al. 1994) . With 63 known breeding

pairs, and an estimated total breeding population

of 100-120 pairs (Rabarisoa et al. 1997), it is

among the most endangered birds of prey in the

world (Langrand and Meyburg 1989, Watson et al.

1993, 1996). Madagascar Fish-Eagles exhibit an un-

usual dispersal and breeding strategy, possibly re-

stricting the species’ distribution and abundance

280

December 2002 Relaxedness of Madagascar Fish-Eagles 281

through limited dispersal or occurrence of in-

breeding. Breeding was believed to be monoga-

mous, but at 46% of known nests, a third, and

sometimes a fourth adult is involved with the

breeding activities of the primary pair (Watson et

al. 1999). Based on banding studies at several nests

(Watson et al. 1999), extra-pair birds were believed

to be progeny (possibly only male) from previous

years. Such delayed dispersal can result in forma-

tion of cooperative breeding groups, a relatively

rare breeding system among birds (Stacey and Ko-

enig 1990, Ligon 1999), especially among raptors

(Simmons 2000, and references therein). Ecologi-

cal or behavioral factors may influence evolution

of cooperative breeding strategies (Newton 1979,

Oring 1986, Faaborg and Bednarz 1990, Stacey and

Koenig 1990, Sherman 1995), and contribute to

attendance of additional adults at Madagascar Fish-

Eagle nests. Understanding dispersal and repro-

ductive strategies is critical for developing a man-

agement plan to ensure the species’ survival.

DNA markers have been applied to a variety of

questions regarding conservation of birds (Haig

and Avise 1996) . DNA fingerprinting proved useful

to assess relatedness at the nest (Westneat 1990,

Wetton et al. 1992, Haig et al. 1993, 1994a, 1994b)

and population (Triggs et al. 1992, Fleischer et al.

1994) levels, to infer species-level population ge-

netic structure (Longmire et al. 1991), and to es-

timate relatedness in captive stocks (Kirby 1990:

239). We used DNA fingerprinting to determine

paternity among Madagascar Fish-Eagle adults at-

tending a nest, and to examine the level of relat-

edness among adults within and between nests.

Methods

Samples. We studied three trios and one quartet of

fish-eagles at a site in west-central Madagascar (19°S,

44°30'E) on a daily basis during one breeding season

from 24 June-5 October 1999. The area is tropical decid-

uous dry forest containing several lakes (3.09-4.86 km^)

and supports 11 fish-eagle territories (Rabarisoa et al.

1997). Eagles were marked and are referred to by num-ber. Nest sites are referred to by location and nest num-ber (Ankerika 4, Befotaka 2, Befotaka 3, and Soamalipo

2). A dominance hierarchy was observed at each nest

based on aggressive interactions between adults. Aerial

pursuits (chasing) and physical displacements from ei-

ther the nest or from perches within 200 m of the nest

tree, often accompanied by a distinctive ‘displacement’

call, were observed throughout the breeding period andwere interpreted as signs of aggression (Tingay 2000).

Males are referred to as either dominant (a), or subor-

dinate ((3 or y). We were unable to establish the domi-

nance hierarchy at nest site Befotaka 3. Nestlings were

briefly removed from the nest at ca. 7 wk of age andbanded. Blood (0.1-0.25 ml) was taken from the brachial

vein (Tingay 2000), immediately placed in 4.5 ml of lysis

buffer (100 mM, pH 8.0, 100 rriM EDTA, 10 niM NaCil,

0.5% SDS) in a polypropylene tube, labeled, and stored

at ambient temperature.

DNA Purification. Approximately 200 |xl of blood/buffer solution was placed in 800 fxl lysis buffer for 10

min. Protein digestion was performed with 500 (xl of su-

pernatant from the first step, 500 |xl of fresh lysis buffer,

and 0.5 mg/ml proteinase K, with incubation at 37°Covernight. Extractions were performed in 1:1 phenolchloroform, and 24:1 chloroform : isoamyl alcohol. DNAwas precipitated using cold 95% ethanol and 5% samplevolume of 5M (0.082M final) ammonium acetate. DNAwas resuspended in 25 |xl deionized water and stored at

-20°C.

DNA Fingerprinting. DNA samples were digested sep-

arately with Hinfl, Rsal, and Haelll. Digests were loaded

onto 1% TBE agarose gels (20 cm X 24 cm), and sub-

jected to electrophoresis (Sambrook et al. 1989) at 32 Vfor 25 hr. Identity Sizing Standard (Lifecodes Corpora-

tion, Stamford, CT) was placed in several lanes of the gel

to provide molecular weight markers. DNA in the gel was

stained using ethidium bromide, photographed using fWluminescence, and transferred (Southern 1975) onto a

MagnaCharge 0.45 micron nylon membrane (Micron

Separations Inc., Westborough, MA).

Jeffreys et al

(1985) and Jeffreys (1987) minisatellite probe 33.15 was

hybridized using the NICE hybridization solution (Life-

codes Corporation, Stamford, CT) onto digested, im-

mobilized DNA. Both the 33.15 probe and Identity Sizing

Standard were labeled with NICE chemiluminescenceUnhybridized probe and size standard were washed fromthe membrane using Quick-Light wash solutions (Life-

codes Corporation) . The hybridized probe was illuminat-

ed with Lumi-Phos 480 (I.ifecodes Corporation) and vi-

sualized by exposure to Kodak XAR5 X-omat film.

DNA Fingerprinting Analysis. Gels were arrayed with

samples from individuals attending a nest adjacent to oneanother. If all hybridization bands observed for nestlings

could have been inherited from the primary pair, we con-

cluded that the primary pair was the parents. If, however,

a hybridization band could be accounted for only by par-

entage by a nest attendant, we concluded that an extra-

pair mating had occurred. There was only one adult fe-

male at each nest. The male that was most dominant andexhibited the greatest paternal investment (Tingay 2000)

was considered the male of the primary pair.

DNA band-sharing (Bruford et al. 1992) was calculated

as S = 2n^y/ (n^ + riy), where = the number of bandsshared by both individuals, = the total number of

bands exhibited by individual x, and = the total num-ber of bands exhibited by individual y. Band-sharing was

estimated for all combinations of individuals in this study

The range of S for known parent-offspring combinations

provided a quantitative expectation of how many bandsmust be shared before a hypothesis of familial related-

ness was supported.

Results

Parentage Assessment of Nestlings and Juve-

niles. DNA fingerprinting techniques were used to

282 Tingay et al. VoL. 36, No. 4

assess relatedness of 17 eagles at four nests. Twoenzymes {HaAll and RscH) produced clearly inter-

pretable results yielding a total of 34 bands scored,

24 of which were variable and 10 invariant (Table

1). Of the 24 variable bands, six were informative

in determining one or more possible parents for

the two nestlings at Soamalipo 2; three for the ju-

venile at Befotaka 3; and seven for the nestling at

Befotaka 2. Blood samples were available only for

adults at Ankerika 4. A nest-by-nest assessment of

parentage is presented below.

Befotaka 2. Female 121, a male 118, and P male

8 attended the nest. Nestling 47 shared three var-

iant /facIII and one variant Bsdi hybridization

bands with adult female 121,and two variant 7/fldlI

and one variant hybridization bands with pmale 8 ,

suggesting that subordinate P male 8 was

the father of the nestling 47, and not a male 118.

Befotaka 3. Female 6,potential a male 48, and

potential a male 150 attended this nest. Juvenile

128 shared one HadW band and one Rsa\ bandwith adult female 6 . Banding records show that ju-

venile 128 fledged from this nest in 1998. Although

band sharing showed it unlikely that either adult

male at the nest in 1999 (48 and 150) was the fa-

ther, it is highly probable that the adult female at

the nest is the mother {S — 0.95 is the highest

value in the study, female 6 has been recorded at

this nest site every year since 1993, and no other

female has been recorded at this nest).

Soamalipo 2. Female 103, a male 5, p male 136,

and 7 male 30 attended this nest. Nestling 68

shared one HaeWl band with adult female 103 and

two bands with 7 male 30. Nestling 00 shared

one HadW and one Rsoi band with adult female

103 and one HaeWl and three Rsai bands with 7male 30. The apparent father of both nestlings is

subordinate 7 male 30.

Relatedness Estimates of All Adults Within and

Between Nests. Among 136 pairwise comparisons,

band-sharing among individuals ranged from 0.58-

0.95, with a mean value of 0.79. Partitioning pair-

wise band-sharing into within- and between-nest

components showed no difference (mean S — 0.80

within nests and 0.79 between nests). After ac-

counting for eight known first-order relative pairs

(parent-offspring, full-sibling), band-sharing was

higher among first-order relatives (v = 0.87, range

= 0.82-0.95) than overall (x = 0.79; Table 2). Us-

ing these findings, relatedness among adults at-

tending nests (male-male, male-female) was deter-

mined (Table 2).

Ankerika 4. Band-sharing values suggested a po-

tential first-order relationship between female 113

and a male 31, but not between the female 113

and P male 34. Band-sharing suggested that the

males were unrelated.

Befotaka 2. Band-sharing values did not support

a first-order relationship between the female and

either male, nor between males. P male 8 had two

bands not shared with any individual within the

study population; trapping records indicate that pmale 8 fledged from the Befotaka 3 nest in 1993.

Befotaka 3. Band-sharing values indicated a po-


and male 150, but not between female 6 and male

48. Band-sharing suggested that the males were un-

related.

Soamalipo 2. Band-sharing values indicated a po-


and a male 5, but not between female 103 and the

two subordinate males (P 136 and 7 30). Band-

sharing between a male 5 and 7 male 30 indicated

a potential first-order relationship.

Relatedness estimates between nests. Comparingamong nests, we observed high band-sharing val-

ues between female 121 (Befotaka 2) and female

103 (Soamalipo 2), male 5 (Soamalipo 2) and male

48 (Befotaka 3), and between male 34 (Ankerika

4) and female 6 (Befotaka 3) ,suggesting potential

first-order relatedness between these pairs of

adults.

Discussion

Subordinate males may have fathered all nest-

lings in this study. At Soamalipo 2, one subordinate

male appeared to have fathered both nestlings,

however, because a male 5 and 7 male 30 are close

relatives, and because of missing data for a male

5, we cannot exclude a male 5 as a possible father

of one or both nestlings. At all nests, paternity by

subordinates could have occurred by chance, as all

attending males copulated with the female (Tingay

2000). Paternity by subordinates was surprising giv-

en that dominant males invested more energy to

the nesting attempt than subordinate males (Tin-

gay 2000). This level of dominant male investment

may be explained by the apparent first-order relat-

edness of the female and the dominant male at

three of four nests (Ankerika 4, Befotaka 3, and

Soamalipo 2). Because 50% of alleles are shared

with a first-order relative, and 25% with an off-

spring of a first-order relative, then shared alleles

are transmitted to the next generation if a first-

December 2002 Reiatedness of Madagascar Flsh-Eagles 283

Table 1. DNA fingerprinting hybridization bands (Jeffreys 33.15 probe) observed for individual Madagascar Fish-

Eagles. Bands are designated by enzyme used (H = Hae\\\ or R = Rsai) and molecular weight of bands in kilobase

pairs. Sex and rank for individuals is indicated (F = female, aM = alpha male, pM = beta male, yM = gamma male,

NSL = nestling, JUV = juvenile).

Ankerika 4^ Befotaka 2'’ Befotaka 3'= Soamalipo 2^

F aM (3M F aM (3M ;NSL F aM? aM? JUV F aM PM yM NSL NSLIndividual 113 31 34 121 118 8 47 6 150 48 128 103 5 136 30 68 00

Bands

H 16.0 + + + + + + + + + + 4 4 4 4 4 4 4H 10.7 -F + + 4 4H 8.5 + + + + + + + + + 4 4 4 4 4 4 4 4H 7.3 + + + + + + + 4 4 4 4 4 4H 6.5 + + + + 4H 6.0 -F -F -F 4 4H 5.7 + + + + 4 4H 5.6 + + 4H 5.2 + 4H 4.9 -F -F 4 4H 4.7 +H 4.5 + + + + + + + 4 4 4 4 4 4 4H 3.9 + + + + + + + + + 4 4 4 4 4 4H 3.6 -F -F -F + + 4 4 4H 3.2 + + + + + + + + 4 4 4H 2.9 + + + + + + + + + 4 4 4 4 4 4 4 4H 2.7 + -F + + + + + + 4 4 4 4 4 4 4 4H 2.6 + + + + -F -F -F -F -F 4 4 4 4 4 4 4 4H 2.2 + + + + + + -F + + 4 4 4 4 4 4 4 4H 1.5 + + + + + + + + + 4 4 4 4 4 4 4 4H 1.4 -F -F -F + -F -F + + + 4 4 4 4 4 4 4 4H 1.0 + + + + 4 4 4 4 4 4 4H 0.9 + + + + + + + 4 4 4 4 4R 12.0 + + + + + + + + + 4 4 4 ? 4 4 4 4R 5.2 -F -F -F -F ?

R 5.0 + + + + + + 4 ? 4 4 4R 4.7 + + 4 ? 4 4 4R 4.5 + ?

R 4.4 + -F -F -F -F 4 ? 4R 4.2 + ? 4 4R 3.3 + + + + + + + + 4 4 4 ? 4 4 4 4R 1.5 + + + 4 4 ? 4 4 4 4R 1.4 + + + -F -F -F -F 4 4 ? 4 4 4R 1.2 4 + + + + + + + + 4 4 4 ? 4 4 4 4

Total No. bandsper individual 21 21 22 20 20 22 26 21 21 20 19 21 14 19 21 20 23

^Fifteen bands are variable at Ankerika 4 (H 7.3, H 6.5, H 6.0, H 5.7, H 5.6, H 4.9, H 3.6, H 1.0, H 0.9, R 5.2, R 5.0, R 4.7, R 4 4,

R 1.5, R 1.4). All other bands are invariant.

Of the variable bands at Befotaka 2, six are shared between the nestling and the female (H 10.7, H 4.5, H 3.6, H 1.0, R 5.0, R 1 5),

six are shared between the nestling and the beta male (H 6.5, H 6.0, H 0.9, R 5.2, R 4.4, R 1.4); one is shared between the nestling,

female, and beta male (H 3.2); and four are variable but are not observed in tbe nestling (H 5.7, H 5.2, H 4.7, R 4.5). All other

bands are invariant.

Of the variable bands at Befotaka 3, four are shared between the juvenile and the female (H 7.3, H 6.5, H 3.6, R 4.7); and ten are

variable but are not observed in the juvenile (H 10.7, H 6.0, H 5.7, H 5.6, H 4.9, H 3.2, H 1.0, R 5.0, R 4.2, R 1.5). All other bands

are invariant.

Of the variable bands at Soamalipo 2, four are shared between nestling 68 and the female (H 7.3, H 3.9, H 3.2, R 5.0); two are

shared between nestling 68 and the gamma male (R 4.7, R 1.4); and one is shared between nestling 68, the female, and the gammamale (H 4.5). Five bands are shared between nestling 00 and the female (H 3.9, H 3.6, H 3.2, R 5.0, R 4.4); four are shared between

nestling 00 and the gamma male (H 0.9, R 4.7, R 4.2, R 1.4); and one is shared between nestling 00, the female, and the gammamale (H 4.5). Five are variable but are not observed in either nestling (H 10.7, H 6.0, H 5.7, H 5.2, H 4.9); and all other bands are

invariant.

284 Tingay et al. VoL. 36, No. 4

be 2G O

S 2 ^be cu

g^

S II

. C/!)

^ 2;QO

2"

2s

cn

>•-.

tu,!-i

o1)

fl

daouVud

Cl

o’J}

da

i -

^ be ^I, C

GX >- ^

c VS0 a;i.1

a V dr“H 1

G1-H B XCO G ’GCO ?GX X2 II

'—J GCL

be „

.a 2^ l=i

GOw2ri

ce

ao

-GGrt

svs•i—

<

d'daVbe!=!

QCfi

Gtj

O

G uX •J-i

vsOJ2 a

II

S aS GaX ^jSX X

aa; X

GII 2 GX !i

0TJa; 0 2u G ^T3G

2t/2

o;

Gt3

2_G

,0

>

c a

S GT3 XG OJ

G C/D

X).

V £vs

?5-h

Ph

dV Xu cu

u c• I-^

cu d*

vs HOJ 0

u>

OJ0

dd vs

•w0 vsXJ OJ

c"d 1

OJ cT!c

OJ

OJ

c/s vs

GT3 O

o 2Cfl

CG

bodW

I

VS

CM

rO

uduvs

dbed

abeGd

cvr

O

9

0c/)

JC/D O2

2 ^

S o^ GO

GOGO.

a

GOo

> 00

2 2i

CO

2 o2 »-o

2 ^

COQO

O I>QO J>

d d

^ XI ocI> 00 00

d d d

CO O 1—I X

00 00 i> 00

d d d d

xO X GO 0 CM!>• 00 X X Xd d d d d

GO 0 M GO 0i> C3D J> 00 00

d d d d d

X 0 T~( 0 10 X Xx> 00 X X 0 r- Xd d d d d d d

00 in X 10 Xi> O) X X X GO 00

d d d d d d d00

d

»oi>eoo mXi-Hi>GOoqi^oooo cc cc COdddd ddddd

accu.

cc

|b-i CM

CD. GO

2u

cn

DQ

aG/C

CO CJD X X 0 CO 03 in00 tr^ j> i> i> 00 in X I>

d d d d d d d d d d

X X GO X 0 cvr X 03 i> CO mi> X X 00 i>

d d d d d d d d d d d

m 1'' 1'' CO X 0 i> CO CO (M X 0X 00 QO X 03 X X i> 03

d d d d d d d d d d d d

X 1—

H

QO X Tf CO 03 X X 0 1

—1

X" X X'' X X X X X l'^ X X X'- Xd d d d d d d d d d d d d

m CO X rH X m X 0 0 X GOX 00 X X^ (X 00 i> X X X x^ 00

d d d d d d d d d d d d d d

X 03 X X 03 X X CO m 1-H 0 rH CO00 t> X-; 00 00 00 i> 00 QO x> 00 00

d d d d d 0 d d d d 0 d d d d

T—

H

OC X 0 CC 00 GO 1-0 X 0 XQO X CM i—H 1-0 CM 0 QO QO X

T—

H

T“^ 1—

H

!

—

H

hJXn.

s S S1

HHC/D

a cn Ph a ca 2 Ph a a a (TL 2

CMd d

24’E dOJ

-uj

2G OJ

CQ

COM0

d CGM Xd G-(-J

2 aG

u 0PQ X

NSL

0

0.86

0.73

0.89

0.84

0.79

0.71

0.86

0.91

0.77

0.79

0.81

0.86

0.86

0.67

0.82

0.88

Deciembkr 2002 REIATEDNESS of MADACiASCAR FiSH-EAGI.ES 285

order relative reproduces successfully. At Soamali-

po 2, the dominant male gained an additional ge-

netic advantage by having two potential hrst-order

relatives at the nest (the female and the y male).

It would be advantageous to be a male at the same

nest as a brother, because if either mated success-

fully, then shared genes are transmitted to the next

generation. Although a strategy of assisting repro-

ductive efforts of close relatives may be advanta-

geous for some Madagascar Fish-Eagles, apparently

it is not the only strategy in use. At Befotaka 2, the

dominant male was not the father, and nor was he

a first-order relative of either the female or the sub-

ordinate male.

At Befotaka 3, ajuvenile female did not disperse.

This is the hrst observed instance of a female nest-

ling from a previous year remaining at a nest (Ra-

fanomezantsoa 1997). Flere, delayed dispersal was

not associated with observed helping activity, yet

the female juvenile was tolerated at the nest. Al-

though inconclusive, our findings do not exclude

the delayed dispersal hypothesis.

Between-nest relatedness comparisons revealed

that some adults had a potential close relative (par-

ent-offspring or full-sibling) at another nest within

the study area. This suggests that hrst-order rela-

tives (excluding nestlings) are as likely to be found

among nests as within a nest.

We are currently investigating the full range of

breeding strategies in the Madagascar Eish-Eagle.

We intend to determine whether this species ex-

hibits genetic monogamy or polyandry by extend-

ing our sample size and duration of study. Studies

of another cooperative polyandrous raptor species,

the Galapagos Hawk {Buteo galapagoensis) has re-

vealed mixed paternity at nests over two consecu-

tive breeding seasons (Faaborg et al. 1995). How-ever, the dominance hierarchy we have observed

among cooperative hsh-eagles has not been docu-

mented among Galapagos Hawks, which may or

may not influence the occurrence of genetic mo-nogamy within polyandrous groups of Madagascar

Fish-Eagles. If delayed dispersal is obligatory in this

species, recolonization of unoccupied habitats mayhave to be promoted by active conservation mea-

sures, such as the translocation of individuals from

other areas. Additionally, copulation by closely-re-

lated pairs, as observed in this study, suggests that

the effects of inbreeding may have to be consid-

ered in conservation planning. For example, if

hrst-order relatives are found to be producing off-

spring, conservation managers may wish to target

some of those specific individuals as likely candi-

dates for translocation, in order to reduce the

probability of further inbreeding and to create an

opportunity for outbreeding with other, genetically

dissimilar, individuals.

Acknowledgments

We conducted this study under The Peregrine Fund’s

Madagascar Fish-Eagle and Wetland Conservation Pro-

ject. We thank the Madagascar Direction des Eaux et For-

ets, Tripartite Commission, Association Nationale pour la

Gestion des Aires Protogees and United Nations Educa-tional, Scientific, and Cultural Organization for collabo-

ration. This work was funded in part by grants from the

Liz Claiborne and Art Ortenberg Foundation, Environ-

ment Now, the John D. and Catherine T. MacArthurFoundation, Biodiversity Support Program, Hawk Moun-tain/Zeiss Optics 1999 Research Award, Jim Brett Global

Conservation Fund and University of Nottingham. Weare grateful to Professor David Parkin for technical assis-

tance with DNA purification, to Jim Berkelman and two

anonymous referees for their thoughtful comments onan earlier draft of this paper, and to Peregrine Fund Field

Manager Loukman Kalavah for expertise in the field

Literahjre Cited

Bruford, M.W., O. Hanotte, J.F.Y. Brookfield, and TBurke. 1992. Single-locus and multilocus DNA finger-

printing. Pages 225-269 ire A.R. Hoelzel [Ed.], Molec-

ular genetic analysis of populations: a practical ap-

proach. IRE Press, Oxford, U.K.

Coliar, N.J., M.J. Crosby, and A.J. Stattersfield. 1994

Birds to watch 2: the world list of threatened birds

BirdUife International, Cambridge, U.K.

Faaborg, J. and J.C. Bednarz. 1990. Galapagos and Har-

ris’ Hawks: divergent causes of sociality in two raptors

Pages 359-383 in P.B. Stacey and K.W. Koenig [Eds ]

,

Co-operative breeding in birds: long term studies of

ecology and behaviour. Cambridge Univ. Press, Cam-bridge, U.K.

, P.G. Parker, U. Df.Uay, TJ. deVries, J.C. Bednarz,

S. Maria Paz, J. Naranjo, and TA. Waite. 1995. Con-

firmation of co-operative polyandry in the Galapagos

Hawk (Buteo galapagoensis). Behav. Ecol. Sociohiol. 36:

83-90.

Fieischer, R.C., C.L. Tarr, and T.K. Pratt. 1994. Ge-

netic structure and mating system in the Palila, an

endangered Hawaiian honeycreeper, as assessed by

DNA fingerprinting. Mol. Ecol. 3:383-392.

FIaig, S.M., J.R. Belthoff, and D.H. Ailen. 1993. Ex-

amination of population structure in Red-cockaded

Woodpeckers using DNA profiles. Evolution 47:185-

194.

? J-b- Ballou, and NJ. Casna. 1994a. Identifica-

tion of kin structure among Guam rail founders a

comparison of pedigrees and DNA profiles. Mol. Ecol

4:109-119.

, J.R. Wai.ters, andJ.H. Plissner. 1994b. Genetic

286 Tingay et ai.. VoL. 36, No. 4

evidence for monogamy in the Red-cockaded Wood-

pecker, a cooperative breeder. Behav. Ecol. Sociobiol. 23:

295-303.

AND J.C. Avise. 1996. Avian conservation genetics.

Pages 160-189 mJ.C. Avise and J.L. Hamrick [Eds.],

Conservation genetics: case histories from nature.

Chapman and Hall, New York, NY U.S.A.

Jeffrey, A.J. 1987. Highly variable minisatellites and

DNA fingerprints. Biochem. Soc. Trans. 15:309-317.

, V. Wilson, and S.L. Thein. 1985. Individual-spe-

cific “fingerprints” of human DNA. Nature 316:76-79.

Kirby, L.T. 1990. DNA fingerprinting: an introduction.

Stockton Press, New York, NY U.S.A.

Langrand, O. and B.-U. Meyburg. 1989. Range, status,

and biology of the Madagascar Sea-Eagle Haliaeetus

vociferoides. Pages 269-278 in B.-U. Meyburg and R.D.

Chancellor [Eds.], Raptors in the modern world.

WWGBP, Berlin, Germany.

Eicon, J.D. 1999. The evolution of avian breeding sys-

tems. Oxford Univ. Press, Oxford, U.K.

Longmire, J.L., R.E. Ambrose, N.C. Brown, TJ. Cade,

T.L. Maechtle, S.W. Seegar, F.P. Ward, and C.M.

White. 1991. Use of sex-linked minisatellite fragments

to investigate genetic differentiation and migration of

North American populations of the Peregrine Falcon

{Falco peregrinus)

.

Pages 217-229 in T. Burke, G. Dolf,

A.J. Jeffreys, and R. Wolff [Eds.],DNA fingerprinting:

approaches and applications. Birkhauser-Verlag, Ba-

sel, Switzerland.

Newton, I. 1979 Population ecology of raptors. Poyser,

London, U.K.

Oring, L.W. 1986. Avian polyandry. Pages 309-351 mR.J.

Johnston [Ed.], Current ornithology. Vol. 3. Plenum

Press, New York, NY U.S.A.

Rabarisoa, R., R.T. Watson, R. Thorstrom, and J.Ber-

KELMAN. 1997. Status of the Madagascar Fish-Eagle in

1995. Ostrich 68:8—12.

RaFANOMEZANTSOA, S. 1997. Behaviour and natal dispers-

al of fledgling Madagascar Fish-Eagles. Pages 403-41

1

in R.T. Watson [Ed.], Madagascar wetlands conserva-

tion project, progress report 3, 1995-1996. The Per-

egrine Fund, Boise, ID U.S.A.

Sambrook, J., E.F Fritsch, and T. Maniatis. 1989. Mo-

lecular cloning: a laboratory manual, 2nd Ed. Cold

Spring Harbor Press, New York, NY U.S.A.

Sherman, P.T. 1995, Social organisation of co-operatively

polyandrous White-winged Trumpeters {Psophia leu-

coptera) in Peru, Auk 112:296-309.

Simmons, R.E. 2000. Harriers of the world: their behav-

iour and ecology. Oxford Univ. Press, Oxford, U.K,

Southern, E.M. 1975. Detection of specific sequences

among DNA fragments separated by gel electropho-

resis.J.Mol Biol 98:503-527.

Stacey, P.B. and W.D. Koenig (Eds.). 1990. Co-operative

breeding in birds: long term studies of ecology and

behaviour. Cambridge Univ. Press, Cambridge, U.K.

Tingay, R. 2000. Sex, lies, and dominance: paternity and

behaviour of extra-pair Madagascar Fish-Eagles Hal-

iaeetus vociferoides. M.S. thesis, University of Notting-

ham, Nottingham, U.K.

Triggs, S.J., M.J. Williams, S.J. Marshall, and G.K.

Chambers. 1992. Genetic structure of Blue Duck {Hy-

menolaimus malacorhynchus) populations revealed by

DNA fingerprinting. Auk 109:80-89.

Watson, R.T., J. Berkelman, R. Lewis, and S. Razafin-

dramanana. 1993. Conservation studies on the Mad-

agascar Fish-Eagle Haliaeetus vociferoides. Proc. Pan-Afr.

Ornithol. Cong. 8:192-196.

, S. Thomsett, D. O’Daniei., and R. Lewis. 1996

Breeding, growth, development, and management of

the Madagascar Fish-Eagle {Haliaeetus vociferoides).]

Raptor Res. 30:21-27.

, S. Razafindramanana, R. Thorstrom, and S. Ra-

fanomezantsoa. 1999. Breeding biology, extra-pair

birds, productivity, siblicide, and conservation of the

Madagascar Fish-Eagle. Ostrich 70:105-111.

Westneat, D.F 1990. Genetic parentage in the Indigo

Bunting: a study using DNA fingerprinting. Behav

Ecol. Sociobiol. 27:67-76.

Wetton, J.H., D.T. Parkin, .and R.E. Garter. 1992. Use

of genetic markers for parentage analysis in Passer do-

mesticus (house sparrows). Heredity 69:243-254.

Received 26 November 2001; accepted 23 July 2002

J. Raptor Res. 36(4):287-293


NESTING AND PERCHING HABITAT USE OETHE MADAGASCAR FISH-EAGLE

James Berkelman^ and James D. FraserDepartment of Fisheries and Wildlife Sciences, Virginia Polytechnical Institute and State University,

Blacksburg, VA 24061-0321 U.S.A.

Richard T. WatsonThe Peregrine Fund, 5668 West Flying Hawk Lane Boise, ID 83709 U.S.A.

Abstract.

—

We documented Madagascar Eish-Eagle (Haliaeetus vociferoides) nest and perch use on lakes

and rivers and compared parameters of used trees to unused reference trees. Nest and perch trees were

broader and taller, had more unobstructed branches, and were less obstructed by adjacent trees com-

pared to reference trees. Perch trees also were more often deciduous than reference trees. Nest sites

had more shoreline perch trees than reference sites. Logistic regression models with tree height as the

independent variable distinguished nest and perch trees from randomly selected reference trees. Models

with number of perch trees along a 1.25 ha (50 m width) shoreline section distinguished nest sites from

reference sites. These models suggest that the presence of trees >15 m tall within 50 m of the shoreline

is a good predictor of Madagascar Eish-Eagle habitat use.

Key Words; Madagascar Fish-Eagle, Haliaeetus vociferoides; habitat; Madagascar, nest tree, perch tree, shore-

line.

USO DE HABITAT DE ANIDACION Y PERCHA DEL AGUILA PESCADORA DE MADAGASCAR

Resumen.

—

-Documentamos el uso de nidos y perchas para el aguila pescadora de Madagascar {Haliaeetus

vociferoides) en lagos y rios y comparamos parametros de arboles usados con arboles no usados de

referenda. Los nidos y arboles percha fueron mas anchos y mas altos, tenian mas ramas despejadas, y

estaban menos obstruidos por arboles adyacentes en comparacion con los arboles referenda. Los arboles

percha fueron ademas algunas veces mas deciduos que los arboles control. Los sitios nido disponian de

mas arboles percha costeros que los sitios de referencia. Los modelos de regresion logistica con la altura

de los arboles como variable independiente distinguieron los nidos y arboles percha de arboles control

seleccionados aleatoreamente. Los modelos con numeros de arboles percha cerca a 1.25 ha (50 m de

ancho) de la seccion de costa distinguieron los sitios nido de los sitios referencia. Estos modelos sugieren

que la presencia de arboles >15 m de alto dentro de 50 m de la linea costera es un buen pronosticador

del uso de habitat del aguila pescadora de Madagascar.


With a population estimate of 99 breeding pairs

(Rabarisoa et al. 1997), the Madagascar Fish-Eagle

{Haliaeetus vociferoides) is one of the rarest birds of

prey in the world (Meyburg 1986). Until recently,

little was known about the species’ ecology and sta-

tus. Langrand and Meyburg (1989) noted that the

Madagascar Fish-Eagle used tall trees near water

for nests and foraging perches, but prior to this

study, there had been no detailed quantitative stud-

' Present address: Department of Wildlife Ecology, Uni-

versity of Wisconsin, 218 Russell Labs, 1630 Linden Dr.,

Madison, W1 53706-1598; e-mail address: jberkelman®

facstaff.wisc.edu

ies of Madagascar Fish-Eagle nesting or perching

habitat use.

Nelson and Horning (1993) estimated from sat-

ellite data that Madagascar’s forest cover had been

reduced to 10.4% of the island by 1990. Nest-site

availability is a key limiting factor for raptor pop-

ulations (Newton 1979). Also perch-tree distribu-

tion is a reliable predictor of Bald Eagle {Haliaeetus

leucocephalus) distribution on the Chesapeake Bay

(Chandler et al. 1995). Thus, we focused our study

on both nest and perch trees, along with the sur-

rounding habitat conditions. The objectives of this

study were to determine characteristics of nest

trees, nest sites, and perch trees used by Madagas-

287

288 Berkelman et al. VoL. 36, No. 4

Table 1. Sites where Madagascar Fish-Eagle nests and perches were investigated in the region of Antsalova, Mada-gascar, 1994. Site names are lakes unless otherwise indicated.

Site Latitude, LongitudeNumber oe

Eagle Pairs

Masiadolo 18°41'S, 44°28'E HBesara 18°41'S, 44°16'E 1

Soahanina River 18°46'-48'S, 44°16'~19'E 3^

Antsahafa 18°48'S, 44°29'E PMasama 18°50'-5TS, 44“28'-29'E 2

Tsiandrora 18°58'S, 44°38'E 1

Andranolava 1'’ 19°0'S, 44°2TE 1

Befotaka 19°1'-2'S, 44°24'-25'E 3

Soamalipo 18°59'-19°2'S, 44°26'-27'E 3^

Ankerika 19°T-2'S, 44'^27'-44°28'E 4

Andranovorimirafy 19°3'S, 44°27'E 1

Andranolava 2'^ 19°4'S, 44°25'E 1

Antsakotsako 19°6'S, 44°33'E 1^

Ampozabe 19°9'S, 44°40'E 1

Bevoay 19°9'S, 44°25'E 1

Manambolo River 19°8'-9'S, 44°44'-49'S 2

Maromahia 19°11'-12'S, 44°37'-38'E 1

Bejijo 19°12'-14'S, 44°32 -33'E 1

No nest was found for one of the fish-eagle pairs at five of the sites.

Two of the lakes in the study had the same name.

car Fish-Eagles and to develop predictive modelsto identify fish-eagle nesting and perching habitat.

SiUDY Area and Methods

We conducted the study during the first half of the

Madagascar Fish-Eagle breeding season from 21 May-14August 1994. We investigated fish-eagle nesting andpeiching habitat in a 3000 km^ area in the Antsalova re-

gion of western Madagascar (18°40'-19°15'S, 44^15'-

44°50'E) that included the drainages of the Manambolo,Beboka, and Soahanina rivers west of the Bemaraha Pla-

teau. Topography consisted of coastal plains and low roll-

ing hills with elevations ranging from sea level to 126 m.Soils were shallow and sandy, and the vegetation was a

patchwork of dry deciduous forest, savanna, wetlands,

mangrove swamps, and rice paddies. The climate was sub-

humid and tropical with a dry season from April-Octo-ber and a wet season from November-March. Mean an-

nual rainfall in the region ranged from 1000-1500 mm(Donque 1972).

We defined a nest tree as any tree in which we ob-

served nest construction, incubation, or brood rearing.

A nest site was the area within 300 m of the nest tree. Apeich tree was any tree in which we observed adult fish-

eagles perching. We measured nest and perch trees ofevery known Madagascar Fish-Eagle pair in the study area

(Table 1). Our perch-tree sample {N = 29) was larger

than our nest-tree sample (N = 24) because we did notfind a nest for five of the fish-eagle pairs.

We measured characteristics of fish-eagle nest trees

and randomly selected reference trees to determine if

trees used by fish-eagles differed from average large trees

(>20 cm diameter at breast height [DBH]) near the

same bodies of water. To compare nest and perch trees

to available large trees, we randomly selected a referencetree for each nest or perch tree. We selected trees at the

same distance from the water as the nest or perch tree

To do this, we measured with a hip chain the distance

from the nest tree to the nearest water (nest-water dis-

tance), from perch tree to nearest water (perch-water dis-

tance), and the distance along the shore between the

nest and perch trees (nest-perch distance). We then ran-

domly selected a shoreline reference point on the samebody of water as the nest tree that we had measured(within 1 .5 km along the banks for nest trees on rivers)

To select each nest reference tree, we went to the

shoreline reference point and moved inland a distance

equal to the nest-water distance and selected the nearest

tree >20 cm in DBH as our nest reference tree. We usedthe same shoreline reference point to select a perch ref-

erence tree by moving the nest-perch distance in the

same direction (left or right) along the shoreline as that

between the used nest and perch trees. We then movedinland the perch-water distance and selected the nearest

tree >20 cm in DBH as our perch reference tree. Weused 20-cm DBH as a minimum size for reference trees

based on the minimum size of Bald Eagle perch trees onthe Chesapeake Bay (Buehler et al. 1992).

We measured DBH of nest trees to the nearest cm andused a clinometer to measure height to the nearest me-ter. We counted branches in the tree canopy that we es-

timated to be >5 cm in diameter and unobstructed for

1 m above and below. We recorded arc of accessibility bystanding at the base of the tree and using a compass to

December 2002 Mada(;asc]AR Fish-Eagle Nests 289

measure the total arc (0°-360°) that was unobstructed by

other trees for an estimated distance of 10 m from the

trunk and 3 m below the tree’s crown (Buehler et al.

1992). We recorded nest-tree species and classified

growth form following Keister and Anthony (1983). Ourclassification was based on the location of the lowest fork

in the trunk, and whether the tree was dead. We classi-

fied growth form as large if the lowest fork was in the

lower third of the trunk, medium if the lowest fork was

in the middle third of the trunk, and small if the lowest

fork was in the upper third of the trunk. We recorded

growth form as dead top if the top third of the crown

was dead and as snag if the entire tree was dead andleafless, regardless of the location of the lowest fork in

the trunk.

We measured minimum distance of each nest tree to

water with a hip chain and minimum distance to humandisturbance, building, road, and fish-eagle nest frommaps and aerial photos. Human disturbances included

agricultural clearings, rice paddies, villages, tombs, andfishermen’s camps. Temporary, seasonal shelters that

were not used during the fish-eagle breeding season were

not considered buildings. There were no paved roads

and few motor vehicles in the area, and the most traveled

roads were traversed by less than one motor vehicle per

day, even in the dry season. Oxcarts frequently were used

to transport materials, so we recorded any oxcart track

as a road.

We considered trees ^6.1 m high and with ^30° ac-

cessibility from the shoreline to be potential perch trees

based on the smallest recorded perch tree used by Bald

Eagles on the Chesapeake Bay (Buehler et al. 1992). Wecounted perch trees within 50 m of the water along a 250

m shoreline section centered on the nest tree or refer-

ence tree (Chandler et al. 1995). We classified mean sur-

rounding canopy height to 5-m intervals ranging from 0-

25 m based on visual observation.

We measured the perch tree that we saw fish-eagles use

most frequently for foraging for each of the 29 fish-eagle

pairs in the study area. Eleven (37.9%) of the pairs were

observed for at least 6 hr, at least once per week during

the breeding season (May-October) in 1992, 1993, and1994 as part of a related study (Watson et al. 1999). Theremaining 18 (62.1%) pairs were observed for at least 6

hr, at least three times per breeding season from 1992-

94. We measured the same tree characteristics for perch

trees that we measured for nest trees.

We tested the null hypothesis of no difference between

trees or sites used by breeding Madagascar Fish-Eagles

and reference trees or sites for each of the numerical

variables using the Wilcoxon signed-ranks test. We paired

each fish-eagle nest or perch tree with the randomly se-

lected reference tree on the same water body. We did not

test for differences in distance to water because this was

a criterion for selecting reference trees. We used the chi-

square test of equal proportions to determine if fish-eagle

habitat use was different from expected use for the fol-

lowing categorical variables: tree species, deciduous ver-

sus evergreen trees, growth form, and surrounding can-

opy height. If >20% of expected values were <5, we used

the likelihood ratio chi-square test statistic (Agresti

1990).

We developed logistic regression models to predict the

probability of fish-eagle use of trees and sites based onthe measured habitat variables using stepwise analysis

Our significance level for variables to both enter and exit

models was P = 0.05. We used dummy variables for

growth form categories in the logistic regression (Hos-

mer and Lemeshow 1989). We constructed classification

tables for each logistic regression model by using the es-

timated logistic probabilities for each tree or site to pre-

dict fish-eagle use (Hosmer and Lemeshow 1989). Weconsidered trees or sites as correctly classified as used hy

fish-eagles if the predicted probabilities were ^0.5.

Resui.ts

Nest-tree Characteristics. Nest construction, in-

cubation, or brood rearing was observed at 21

(87.5%) of the 24 measured nest trees in 1994.

The remaining three nest trees were used in 1993,

but not in 1994. Nest trees were taller, had moreunobstructed branches, and a greater arc of acces-

sibility than reference trees (Table 2). Mean nest-

tree DBH was more than twice that of reference

trees. Twenty-two of 24 (91.7%) nest trees versus

only 14 of 24 (58.3%) reference trees had a >270°

arc of accessibility.

Nest-tree species included Tamarindus indica {N= 7), Cordyla madagascariensis {N = 4), Adansonia

sp. {N — 2), Colvillea racemosa {N — 2), Neobeguea

mahafaliensis {N = 2), Acacia sp. {N = 1), Albizia

greveana {N = 1), Alleanthus greveanus {N =1), Foe-

tidia sp. {N = 1), Pandanus sp. {N = 1), and un-

identified {N = 2). T indica was, the most frequent-

ly recorded species of nest reference tree {N = 6).

Its proportion among nest trees (29.2%) was not

different from its proportion among reference

trees (20.8%) (x^ - 0.44, df = I, P = 0.51). Pro-

portions of nest trees and reference trees in each

growth form class were similar (x^ — 4.58, df — 4,

P — 0.33). Eight of the nest trees (33.3%) and

three (12.5%) of the reference trees were decidu-

ous (x^ = 2.95, df = I, P= 0.09).

Eish-eagle nest-tree use was positively associated

with tree height, producing a logistic regression

model of

0 = 1/1+ exp 5.52 - X 0-38x,

where 0 is the probability of fish-eagle use and x,

is the height of tree i. This model correctly classi-

fied 83.3% of 48 trees measured.

Nest-site Characteristics. Number of shoreline

perch trees was greater at nest sites than at randomsites (Table 3). There was a positive relationship

290 Berkelman et al. VoL. 36, No. 4

Table 2. Characteristics of Madagascar Fish-Eagle nest trees, perch trees, and paired reference trees in the region

of Antsalova, Madagascar in 1994.

Variable

Nest Trees

(V = 24)

X ± SE

(Range)

Paired

Reference

Trees

(N = 24)

X ± SE

(Range) pa

Perch Trees

{N= 29)

X ± SE

(Range)

Paired

Reference

Trees

(N = 29)

X ± SE

(Range) pa

DBH (cm) 87.8 ± 11.8 38.4 ± 4.2 <0.001 65.3 ± 7.2 36.9 ± 3.3 <0.001

(29-245) (22-114) (27-270) (21-120)

Height (m) 18.7 ± 0.8 10.5 ± 0.9 <0.001 16.7 ± 0.8 9.8 ± 0.4 <0.001

(10.7-25.9) (5.0-23.3) (9.4-30.3) (4.9-15.8)

No. of branches’^ 5.5 ± 0.7 3.2 ± 0.8 0.021 7.9 ± 1.2 1.8 ± 0.4 <0.001

(1-14) (0-19) (2-39) (0-15)

Arc of accessibility 346.7 ± 5.4 260.2 ± 25.0 <0.001 336.7 ± 7.1 231.4 ± 21.4 <0.001

(265-360) (0-360) (190-360) (0-360)

* Wilcoxon signed-ranks test significance level.

Number of branches in the tree canopy >5 cm in diameter and unobstructed for 1 m above and below.

Arc (0°-360°) that was unobstructed by other trees ^10 m of the trunk and ^3 m below the crown (Buehler et al. 1992).

between fish-eagle nest-site use and the number of

shoreline perch trees. The model was

9 = 1 1 + exp 3.49 - 2

where 0 is the probability of fish-eagle use and

is the number of perch trees within a 1.25 ha (50

m wide) shoreline section centered on the point

on the shoreline nearest nest tree i. Correct clas-

sification of fish-eagle use for this model was 72.9%

of 48 sites. Minimum distance to human distur-

bance, minimum distance to nearest road, mini-

mum distance to nearest building, and minimumdistance to nearest fish-eagle nest did not differ

between nest sites and random sites (Table 3) . Theproportion of nest sites in each 5 m canopy height

interval did not differ between nest sites and ran-

dom sites (x^ = 4.93, df = 4, P = 0.30). Meandistance to water of nest trees was 70.8 m (SE =

12 6, range = 6.8-199.2 m).

Perch-tree Characteristics. Perch trees were larg-

er (DBH and height), had more unobstructed

branches, and had a greater arc of accessibility

than reference trees (Table 2). Twenty-six of 29

(89.7%) nest trees versus only 16 of 29 (55.2%)

reference trees had a >270° arc of accessibility.

Perch-tree species included Colvillea racemosa (N— 5), Ficus cocculifolia (N =

4), Neobeguea mahafal-

lensis (N = 3), Tamarindus indica (N = 3), Albizia

lebbeck (N — 2), Borassus madagascariensis {N —2),Cordyla madagascariensis (N =

2), Acacia sp. {N ~

1), Adansonia sp. (N = 1), Cedrelopsis grevei {N ~

1), Pandanus sp. (N — 1), Raphia sp. {N = 1), and

unidentified {N — A). T. indica was the most fre-

quently recorded perch reference tree species {N= 10). Its proportion among perch trees (10.3%)

was smaller than among reference trees (48.3%)

(x2 = 5.96, df = 1, P = 0.02).

Perch trees and reference trees had similar

growth forms (x^ = 8.04, df = 4, P = 0.09). Pro-

portion of deciduous trees among perch trees

(34.5%) was greater than among reference trees

(10.3%) (x^ = 4.86, df = 1, P = 0.03).

There was a positive association between fish-ea-

gle perch-tree use and tree height, producing a lo-

gistic regression model of

0 = 1 1 + exp 8.68 2

where 0 is the probability of fish-eagle use and

is the height of tree i. This model correctly classi-

fied 84.5% of 58 trees measured.

Disclissicjn

Nest-tree Use. Madagascar Fish-Eagles used nest

trees that were taller and had a greater DBH, moreunobstructed branches, and a greater arc of acces-

sibility than reference trees. The suhstantial differ-

ence between nest trees and reference trees in

mean height and DBH suggests that the fish-eagle

selects nest trees from among the largest trees

available near water. By placing its nests in the tops

December 2002 Madagascar Fish-Eagi.e Nests 291

Table 3. Characteristics of Madagascar Fish-Eagle nest sites {N = 24) and paired reference sites (N — 24) in the

region of Antsalova, Madagascar in 1994.

Variable

Nest Sites

x± SE(Range)

Paired Random Sites

X ± SE

(Range) pa

Minimum distance to human disturbance'^ (km) 0.8 ± 0.2 0.9 ± 0.1 0.742

(0-2.8) (0-2.8)

Minimum distance to building (km) 1.8 ± 0.4 1.8 ± 0.3 0.814

(0.1-7.7) (0-5.6)

Minimum distance to road (km) 1.7 ± 0.4 1.3 ± 0.3 0.055

(0-8.4) (0-5.4)

Minimum distance to fish-eagle nest (km) 4.8 ± 0.9 4.3 ± 0.9 0.104

(1.3-20.3) (0.4-20.1)

Number of perch trees'^ 30.8 ± 2.3 16.6 ± 1.9 <0.001

(10-53) (0-33)

Wilcoxon signed-ranks test significance level.

'’Human disturbances included agricultural clearings, rice paddies, villages, tombs, and fishermen’s camps.

Number of perch trees within a 1.25 ha (50 m wide) shoreline section centered on the point on the shoreline nearest the nest tree

We considered trees that we estimated to have a height ^6.1 m and >30° accessibility from the shoreline to be perch trees.

of these trees, it maximizes accessibility and visibil-

ity for foraging and territorial defense. These re-

sults were consistent with those reported for other

nesting Haliaeetus species (McEwan and Hirth

1979, Andrew and Mosher 1982, Anthony andIsaacs 1989, Shiraki 1994).

Nest-site Use. Number of shoreline perch trees

was the only variable that differed between nest

sites and random sites. This suggests that the Mad-agascar Fish-Eagle, like the Bald Eagle (Chandler

et al. 1995), may avoid areas without a sufficient

number of foraging perches.

Perch-tree Use. Perch trees were larger in height

and DBH, and had more unobstructed branches,

and had a greater arc of accessibility than refer-

ence trees. Such trees probably have greater access

and provide better visibility over water than other

trees. This is consistent with Bald Eagle perch-tree

use (Stalmaster and Newman 1979, Steenhof et al.

1980, Buehler et al. 1992). Madagascar Fish-Eagle

perch trees were more often deciduous than ref-

erence trees. In contrast with the nest-tree results,

the fish-eagles in this study appeared to avoid T.

indica for perching. T. indica is evergreen and often

has a dense crown; therefore fish-eagles may use

this species less often for perching than leafless

trees or snags.

Model Applications. The models we developed

may be used to identify Madagascar Fish-Eagle

nesting and perching habitat along lakes, rivers,

and estuaries in western Madagascar. They do not

apply to a sub-population of at least 16 fish-eagle

pairs that nest on offshore islands at the north end

of the species’ range (Rabarisoa et al. 1997). Al-

though our sample size was limited, the 29 breed-

ing sites sampled represent 29.3%, of the 99 knownremaining Madagascar Fish-Eagle breeding sites

(Rabarisoa et al. 1997). Bald Eagle managementguidelines recommend conserving mature forest

around existing and potential nest sites (Anthonyet al. 1982, Wood et al. 1989). We offer guidelines

that are more specific to the range of tree sizes anddensities found in the tropical dry forest and sa-

vanna habitats that surround the lakes where Mad-agascar Fish-Eagles occur.

We recommend that areas with a >32/ha density

of trees >15 m tall should receive high priority for

Madagascar Fish-Eagle conservation. Probability

that a shoreline tree would be used by MadagascarEish-Eagles for nesting or perching can be calcu-

lated by inserting tree height into the correspond-

ing logistic equation (Fig. 1 ) . Similarly, number of

perch trees along a 1.25 ha (250 X 50 m) shoreline

section can be used to estimate the probability that

Madagascar Fish-Eagles will use the shoreline sec-

tion for nesting (Eig. 1). These models are best

used under the conditions that were present dur-

ing this study (e.g., same eagle population density,

same time of year) and apply to eagles nesting onlakes, rivers, and estuaries.

Presence of tall trees close to shoreline is the

best predictor of Madagascar Eish-Eagle nest-site

use. The eagles often used the tallest trees near

water both for nesting and for foraging perches.

Rabarisoa et al. (1997) conducted MadagascarFish-Eagle surveys from 1991-95, and found areas

Probability

of

Use

292 Berkelman et al. VOE. 36, No. 4

Nest-tree Height (m)

Perch-tree Height (m)

0 S 10 15 20 25 30 35 40 45 50

No. of Perch Trees

Figure 1. Probability of Madagascar Fi.sb-Eagle use of iiesl trees, perch trees, and nest sites as a I’unclion of nest-

tree height (A), perch-tree height (B), and number of shoreline perch trees (C), in the region ol Antsalova Mada-

gascar, 1994. Probabilities were calculated by inserting dilferent values of the explanatory variable (tree height or

number of perch trees) into the equation resulting from stepwise logistic regression analysis.

Dec.ember 2002 Madagascar Fish-Eagle Nests 293

with dense forest adjacent to water that were un-

occupied by fish-eagles. Watson et al. (1996) are

developing means to augment the hsh-eagle pop-

ulation and seek areas of unoccupied fish-eagle

habitat where young eagles may be released. Ourmodels may be used both to identify areas of suit-

able, but unoccupied, fish-eagle habitat and high

conservation priority areas of occupied habitat.

The Tsimembo Forest surrounding Lakes Befo-

taka, Soamalipo, and Ankerika, where the highest

density of fish-eagles is found (Rabarisoa et al.

1997), should receive highest conservation priority.

The human population density around the lakes

was low until recent years when large numbers of

fishermen began to migrate to the region (Watson

and Rabarisoa 2000). Increased harvesting of tall

shoreline trees by migrant fishermen will have a

negative impact on the fish-eagles. People use the

tallest trees available for dugout canoes and build-

ing materials (Watson and Rabarisoa 2000) andmay prevent regeneration of tall trees by harvest-

ing large amounts of fuel wood to preserve fish by

smoke drying. Deforestation probably has already

substantially reduced the amount of fish-eagle hab-

itat available, and as the human population contin-

ues to increase, available habitat will continue to

decrease unless steps are taken to conserve fish-

eagle habitat.

At^KNOWI TDGMENTS

The Peregrine Fund provided financial and logistical

support for this research. We thank C. Razafimahatratra,

G. Raoelison, J. Mampiandra, and L. Kalavah for help

with data collection. Thanks to J. Rajesy, R. Rabarisoa, R.

I.ewis, P. Ravonjiarisoa, and M. Razafindrakoto for ad-

ministrative and logistical support in Antananarivo and

in the field. We thank C.A. Haas, J.J. Ney, R.G. Oderwald,

D.F. Stauffer, R. Thorstrom, R. Tingay, and A.R. Harmatafor comments on the manuscript.

farERA i t]RE Cited

AciRESTi, A. 1990. Categorical data analysis. John Wiley

and Sons, New York, NY U.S.A.

Andrew, J.M. and J.A. Mosher. 1982. Bald Eagle nest site

selection and nesting habitat in Maryland. J. Wildl.

Manage. 46:383-390.

Anthony, R.G. and F.B. Isaacs. 1989. Characteristics of

Bald Eagle nest sites in Oregon. J. Wildl. Manage. 53:

148-159.

, R.L. Knight, G.T. Ai.ien, B.R. McClelland, and

J.I. Hodges. 1982. Habitat use by nesting and roosting

Bald Eagles in the Pacific Northwest. Trans. N. Am.

Wildl. Nat. Resour. Conf. 47:382-390.

Buehler, D.A., S.K. Chandler, T.J. Meicsmann, J.D. Fras-

er, AND J.K.D. Seegar. 1992. Nonbreeding Bald Eagle

perch habitat on the northern Chesapeake Bay. Wil-

son Bull. 104:540-545.

Chandler, S.K., J.D. Fraser, D.A. Buehler, andJ.KD.Si:egar. 1995. Perch trees and shoreline developmentas predictors of Bald Eagle distribution on Chesa-

peake Bay. y. Wildl. Manage. 59:325-332.

Donque, G. 1972. The climatology of Madagascar. Pages

87-144 in R. Battistini and G. Richard-Vindard [Eds ],

Biogeography and ecology of Madagascar. Dr. W.JunkB.V., The Hague, Netherlands.

Hosmer, D.W., Jr. and S. Lemeshow. 1989. Applied lo-

gistic regression. John Wiley and Sons, New York, NYU.S.A.

Keister, G.P., Jr. and R.G. Anthony. 1983. Characteris-

tics of Bald Eagle communal roosts in the KlamathBasin, Oregon and California. J. Wildl. Manasce. 471072-1079.

Langrand, O. and B.-U. Meyburg. 1989. Range, status,

and biology of the Madagascar Sea-Eagle Haliaeetus

vociferoides. Pages 269-277 in B.-U. Meyburg and R.D.

Chancellor [Eds.], Raptors in the modern world.

WWGBP, Berlin, Germany.McEwan, L.C. and D.H. Hirth. 1979. Southern Bald Ea-

gle productivity and nest site selection. J. Wildl. Man-age. 43:585-594.

Meyburg, B.-U. 1986. Threatened and near-threatened

birds of prey of the world. Birds Prey Bull. 3:1-12.

Nelson, R. and N. Horning. 1993. AVHRR-LAC esti-

mates of forest area in Madagascar, 1990. Int.J. Remote

Sens. 14:1463—1475.

Newton, I. 1979. Population ecology of raptors. ButeoBooks, Vermillion, SD U.S.A.

Rabarisoa, R., R.T. Watson, R. Thorstrom, and J. Ber-

kelman. 1997. Status of the Madagascar Fish-Eagle

Haliaeetus vociferoides in 1995. OVncA 68:8-12.

Shiraki, S. 1994. Characteristics of White-tailed Sea-Eagle

nest sites in Hokkaido, Japan. Condor 96:1003-1008

Stalmaster, M.V. and J.R. Newman. 1979. Perch-site pref-

erences of wintering Bald Eagles in northwest Wash-ington./. Wildl. Manage. 43:221-224.

Steenhof, K., S.S. Berunger, and L.H. Fredrickson.

1980. Habitat use by wintering Bald Eagles in South

Dakota. J. Wildl. Manage. 44:798-805.

Watson, R.T. and R. Rabarisoa. 2000. Sakalava fisher-

men and Madagascar Fish-Eagles: enhancing tradi-

tional conservation rules to control resource abuse

that threatens a key breeding area for an endangeredeagle. Ostrich 71:2-10.

, S. Razaeindramanana, R. Thorstrom, and S. Ra-

FANOMEZANTSOA. 1999. Breeding biology, extra-pair

birds, productivity, siblicide, and conservation of the


, S. Tiiomsett, D. O’Daniel, and R. Lewis. 1996

Breeding, growth, development, and management of

the Madagascar Fish-Eagle {Haliaeetus vociferoides) JRaptor Rei 30:21-27.

Wood, P.B., T.C. Edwards, Jr., and M.W. Collopy. 1989.

Characteristics of Bald Eagle nesting habitat in Flori-

da. /. Wildl. Manage. 53:441-449.

Received 30 November 2001; accepted 9 July 2002

J. Raptor Res. 36(4);294-299


USE OF VEGETATIVE STRUCTURE BY POWERFUL OWLS INOUTER URBAN MELBOURNE, VICTORIA, AUSTRALIA—

IMPLICATIONS FOR MANAGEMENT

Raylene Cooke and Robert Wallis^School ofEcology and Environment, Deakin University, Warrnambool Campus, Warrnambool, 3280 Australia

John WhiteSchool of Ecology and Environment, Deakin University, Melbourne Campus, Burwood, 3125 Australia

Abstract.—The Powerful Owl (Ninox strenua) is Australia’s largest owl and is considered of least concern

nationally. Although a number of studies have reported on the ecology of Powerful Owls inhabiting

forests, few have focused on these owls living in urban areas. We report on the characteristics of different

roost trees used by Powerful Owls in a continuum of habitats from urban Melbourne to the more

forested outskirts. Records of weather conditions and daily temperatures were also analyzed to deter-

mine whether the owls were selecting particular roost trees for specific climatic conditions. We found

that roost-tree height and perch height was highly correlated, with the owls always roosting in the top

one-third of the tree, regardless of the tree height. As ambient temperatnre increased perch height

decreased, and vice-versa, but owls always roosted in the top one-third of the roost tree. Powerful Owls

did not simply move up and down the one tree, but moved to more suitable trees according to the

weather conditions. Hence, the species requires a structurally heterogeneous habitat to provide roost

trees for different temperatures. Eurtherraore, successful management of this species in the future will

require the protection of structurally diverse vegetation.

Key Words: Powerful Owl, Ninox strenua; disturbance, management, temperature, urbanization-, vegetation struc-

ture.

USO DE LA ESTRUCTURA VEGETATIVA POR NINOX STRENUA EN EXTERIORES URBANOS DEMELBOURNE, VICTORIA, AUSTRALIA—IMPLICACIONES PARA EL MANEJO

Resumen.—Ninox strenua es el biiho mas grande de Australia y es considerado nacionalmente de rnenor

interes. Aunque un numero de estudios se han concentrado en su ecologia en bosques, pocos se han

enfocado sobre los que habitan en areas urbanas. Reportamos las caracterlsticas del uso de diferentes

arboles percha utilizados por Ninox strenua en un continuum de habitats desde el Melbourne urbano

hasta los alrededores mas boscosos. Adicionalmente se analizaron los registros de condiciones climaticas

y temperaturas diarias para determinar si los buhos estaban seleccionando arboles percha particulares

debido a condiciones climaticas especificas. Encontramos que la altura de los arboles percha y la altura

de la percha utilizada estaba altamente correlacionados con el uso del tercio mas alto del arbol, sin

tener en cuenta la altura del arbol. Cuando la temperatura ambiente incrementaba la altura de la percha

decrecia, y viceversa, pero los buhos siempre percharon en el tercio mas alto del arbol percha. Los

buhos no se movieron simplemente hacia arriba y ab:qo del arbol, sino que se movieron a arboles mas

adecuados de acuerdo a las condiciones climaticas. Por lo tanto, la espccie requierc un habitat estruc-

turalmente heterogeneo que provea arboles perchas para diferentes temperaturas. Ademas de esto, el

manejo exitoso de esta especie en el futuro requiere de la proteccion de vegetacion estructuralmente

diversa.


The Powerful Owl {Ninox strenua) is the largest

Australian owl. The male is slightly larger than the

female, growing to a length of 65 cm with a mass


of up to 1700 g (Higgins 1999). The Powerful Owl

is a nocturnal predator, with a diet consisting al-

most exclusively of medium-sized, arboreal, mar-

supial prey (Webster et al. 1999, Cooke et al. 2002).

The Powerful Owl is classified nationally as of

294

December 2002 The Powfrfue Owe in Urban Environments 295

“least concern” (rated nationally of conservation

significance, but at the lowest level, Garnett and

Crowley 2000) ,occurring at low densities in south-

eastern continental Australia. Within the state of

Victoria the species is listed as endangered (De-

partment of Natural Resources and Environment,

Victoria 1999) and threatened within the Greater

Melbourne Area (Mansergh et al. 1989). Estimates

of population numbers in the state of Victoria are

less than 500 pairs across the state (Garnett and

Crowley 2000).

The Powerful Owl was once considered to be a

specialist in ecological terms because of its appar-

ently restricted habitat and dietary requirements

(Fleay 1968, Seebeck 1976, Roberts 1977), indicat-

ing that it is vulnerable to habitat modihcation and

that it has specific conservation needs. Recent

studies, however, have contested these earlier find-

ings and consequently have questioned the degree

to which the Powerful Owl is vulnerable to habitat

modification and disturbance (Debus and Chafer

1994, Kavanagh and Bamkin 1994, Pavey et al.

1994, Cooke et al. 1997, Cooke et al. 2002).

Urban and suburban areas surrounding Mel-

bourne have been mostly cleared throughout the

past 100 years, with only small patches of remnant

vegetation remaining. Surprisingly, Powerful Owls

still remain in some urban areas, with one knownbreeding pair located only 18 km from central Mel-

bourne. Powerful Owls have also been recorded

living in close proximity to other Australian cities,

including Brisbane (Pavey et al. 1994, Pavey 1995)

and Sydney (Rose 1993). Tittle research has been

undertaken to determine the resources these owls

require for long-term survival in urban environ-

ments. Here, we describe roost tree characteristics

and features of roosts used in urban and suburban

areas by Powerful Owls. Results from this study are

then used to identify management options for Pow-

erful Owls in urban areas. The results of this study

may also provide valuable information for the fu-

ture management of other top-order raptors with

similar ecological attributes in urban areas.

Study Areas

During this study, we examined how Powerful Owls

used the structure of vegetation in a continuum of en-

vironments ranging from urban Melbourne (two sites),

through the urban fringe (three sites), and into moreforested areas (one site). Each site was selected on the

basis that it had a confirmed breeding pair of owls pres-

ent for several years.

The two sites located closest to Melbourne were the

Yarra Valley Metropolitan Park (100 ha) and WarrandyteState Park (586 ha), which were urban parklands man-aged for public recreation and 18 km and 24 km north-

east of central Melbourne, respectively. Both parks have

been extensively modified in the past and now consist ot

riparian areas and the occasional patch of remnant trees

surrounded fry a matrix of revegetated woodlands.

The next three sites along the continuum were OneTree Hill Reserve (143 ha), Smiths Gully (2.4 ha), andSteels Creek (21600 ha). One Tree Hill Reserve andSmiths Gully are both located 35 km from central Mel-

bourne while Steels Creek is located 65 km from Mel-

bourne. These three sites are all dry, open forests andconsist primarily of different Eucalyptus spp. as upper can-

opy trees with Acacia spp. dominating the middle story.

These three sites are also regularly visited by people andalso show signs of disturbance.

The sixth site along our continuum was Toolangi State

Forest (35 000 ha), which is located 80 km northeast of

Melbourne. This forest is a relatively undisturbed wet

sclerophyll forest dominated by mountain ash {Eucalyptwi

regnans). Middle story species are less common in this

area; however, the understory is dominated by various

ferns and bracken.

Methods

A total of 1300 day visits were made to the six study

sites between 1996-99. During these visits the roost tree

in which the Powerful Owl was located was recorded

Roost trees were those in which Powerful Owls spent time

during the daylight hours.

Here, we examined the different roost trees used by

the Powerful Owl at each of the study sites and the char-

acteristics of each tree used. These included the species

of tree, tree height, and the diameter at breast height

(DBH). Records of weather conditions and daily temper-

atures were also analyzed to determine whether the owls

are selecting particular roost trees for specific climatic

conditions.

Each study site was visited at least once weekly over a

4-yr period and each roost tree was examined for the

presence of the Powerful Owl or evidence that an owl

had used the tree recently. Evidence of usage included

fresh whitewash (excreta) or regurgitated food pellets

Temperature and weather conditions were noted, regur-

gitated food pellets were collected and, in situations

where the Powerful Owl was using the roost tree, the

perch height was measured using a clinometer.

Resutts

The Powerful Owls used 179 individual roost

trees at the six study sites. Twenty different tree

species were used as roost trees. The main trees

used for roosting were Eucalyptus spp. (54%), Aca-

cia spp. (18%), and Leptospermum spp. (15%). Oth-

er roost trees were hazel pomaderris {Pomaderns

aspera), the introduced Monterey pine {Pinus ra-

diata),cherry ballart (Exocarpos cupressiformis )

,

Christmas bush {Prostanthera lasianthos), the non-

296 Cooke et al. VoL. 36, No. 4

Table 1. Roost-tree characteristics at each of the six study sites. Values represent mean ± 1.96 SE.

Site NTree Height

(m) DBH (cm)

Perch Height

(m)

Yarra Valley Metropolitan Park 22 15.7 ± 2.2 55.0 ± 12.2 10.2 ± 1.9

Warrandyte 29 13.3 ± 2.3 40.3 ± 11.3 9.6 ± 2.0

One Tree Hill 22 16.2 ± 1.9 48.8 ± 10.0 12.2 ± 1.9

Smiths Gully 24 12,7 ± 1.8 37.1 ± 9.7 8.1 ± 1.1

Steels Creek 23 16.1 ± 2.2 38.5 ± 5.0 10.3 ± 1.9

Toolangi 59 13.0 ± 2.1 49.7 ± 9.6 11.2 ± 1.8

Pooled data 179 14.4 ± 0.9 45.6 ± 4.4 10.4 ± 0.8

indigenous sweet pittosporum (Pittosporum undu-

latum), and swamp paperbark {Melaleuca ericifolia).

To determine whether the dimensions of roost

trees varied between sites we compared the tree

height, roost height, and DBH of roost trees at

each site (Table 1). Roost tree heights were not

different among the six study sites (T5 173 = 1.856,

P = 0.104), with the mean height of roost trees

being 14.4 m ± 0.9 m (±1.96 SE). Perch heights

between the six study sites also did not differ sig-

nificantly (fy 173 = 1.643, P = 0.15), with the meanperch height being 10.4 m ± 0.8 m (±1.96 SE).

There was also no significant difference in the

DBH of the roost trees between the six study sites

( 5 ,i 7s“ 1.52, P — 0.186). Overall, the mean DBH

was 45.6 cm ± 4.4 cm (mean ± 1.96 SE). These

results suggest that the trees used for roosting have

similar physical dimensions at each site even

though the tree species may differ between sites.

0.90

01 0.85'5

z$ 0.80

o 0.75

% 0.70Q.

&0. 0.65n

" 0.60

i 0.55£® 0.500. YVMP One Tree Hill Steels Creek

Warrandyte Smiths Gully Toolangi

Site

Figure 1. Perch heights as a proportion of tree heights

(mean ± 1 and 1.96 SE) at each of the six study sites.

Plots with the same letters indicate homogeneous groups

as revealed by the Student Newman-Keuls (P < 0.05).

YVMP = Yarra Valley Metropolitan Park.

Given the variety of tree species used by the owls

for roosting, we decided to determine whether the

roost trees were being used in a similar fashion

among sites. Specifically, the relationship between

perch height and tree height was examined. Over-

all, perch height was positively correlated with tree

height (r = 0.91, P < 0.001, N = 179). Hence,

although the species of roost tree varied, the owls

tended to perch toward the top of the selected

roost tree. The perch height as a proportion of

tree height varied significantly between sites (E5 173

= 17.76, P < 0.001). Perch heights at the Yarra

Valley Metropolitan Park, Warrandyte State Park,

Smiths Gully, and Steels Creek were lower within

the roost trees than those in Toolangi State Forest

(Student Newman-Keuls test, P < 0.05; Fig. 1).

Although the mean perch height as a proportion

of the tree height varied among sites, roost tree

height was a predictor of perch height within each

site (Fig. 2). High values at all sites (except

Smiths Gully) suggest that there was a strong and

consistent relationship between perch height and

tree height (Table 2).

To further understand this relationship, a com-

parison was made between perch height and dif-

ferent temperature and weather conditions. Whenthere was no precipitation a strong negative asso-

ciation between temperature and perch height was

found (Table 3), with the owls at all sites choosing

lower perch heights as the temperature increased.

On days where rainfall occurred this trend was less

evident, with the owls at most sites showing no con-

sistent association between perch height and tem-

perature (Table 3).

Discussion

The Powerful Owls inhabiting the six study sites

used 179 roost trees. Of these, 87% were from only

Perch

Height

(m)

Perch

Height

(m)

Perch

Height

(m)

December 2002 The Powereul Owl in Urban Environments 297

Yarra Valley Metropolitan Park Warrandyte State Park

Perch height = -1.78 + 0.76 * tree height Perch height = -1.05 + 0.80 * tree height

One Tree Hill Reserve Smiths Gully

Perch height » -2.48 + 0.90 * tree height Perch height = 2.51 + 0.44 * tree height

Tree Height (m)

Steels Creek

Perch height = -1.66 + 0.74 * tree height

Toolangi State Forest

Perch height = -0.38 + 0.89 * tree height

Figure 2. The relationship between perch height and tree height at each of the six study sites. Lines indicate the

regression lines with 95% confidence limits.

298 Cooke ei ai.. VoL. 36, No. 4

Table 2. Regression results of the relationship between

perch height and tree height at all sites.

Site B? df F P

Yarra Valley

Metropolitan Park 0.844 1, 20 114.71 <0.001*

Warrandyte 0.859 1,27 171.34 <0.001*

One Tree Hill 0.825 1, 20 100.33 <0.001*

Smiths Gully 0.463 1, 22 20.84 <0.001*

Steels Creek 0.718 1, 21 56.89 <0.001*

Toolangi 0.980 1, 57 2792.09 <0.001*

* Represents a significant relationship between perch height and

tree height.

three different genera, Eucalyptus (54%), Acacia

(18%), and Leplospermum (15%). The other 13%of roost trees consisted of a variety of genera that

were infrequently used by Powerful Owls. Overall,

Powerful Owls roosted in 20 different tree species

at the six study sites and in most cases the roost

trees used were the most common species at the

specific study site. This indicates that the Powerful

Owls in the Yarra Valley corridor are probably us-

ing abundant and available tree species rather than

selecting less common species.

Roost tree characteristics such as height, perch

height, and DBH did not differ between the six

sites. Roost tree height and perch height, however,

were highly correlated, indicating a direct relation-

ship between the height of the roost tree and the

perch height. Powerful Owls observed at all six

sites generally roosted in the top one-third of the

roost tree, regardless of the tree height.

Overall, these results suggested that Powerful

Owls roosted in a number of tree species and they

were most likely found in the most common tree

species. It is probable that Powerful Owls are gen-

eralists in terms of the tree species in which they

will roost. The fact that the roost tree characteris-

tics (e.g., perch height, DBH) were similar at all

sites suggested that there was some degree of se-

lection of individual trees that offer optimal roost

characteristics. This was particularly highlighted by

the relatively small number of roost trees used at

each site compared with the number of trees avail-

able.

When temperature and weather conditions were

considered in relation to roost tree usage, the re-

sults suggested that as temperature increased

perch height decreased, and vice-versa. On hot

days. Powerful Owls were roosting lower in shadier

sites and on cooler days they roost at higher levels,

possibly to absorb sunlight. However, independent

of the height of the roost tree the Powerful Owls

still roosted in the top one-third of the roost tree.

This result suggests that they require habitats with

a large degree of structural variation to provide

roost trees for different temperatures.

The choice of roost trees used by the Powerful

Owls in clear and rainy conditions was also exam-

ined. The results showed that there was no signif-

icant difference in the perch height used by the

Powerful Owls at five of the six sites on wet days.

Steels Creek was the only exception to this pattern.

At most sites, Powerful Owls roosted in slightly low-

er trees on rainy days. However, at Steels Creek the

Powerful Owls actually roosted in taller, canopy

trees on precipitation days. Thus, it would appear

that the height at which Powerful Owls roost in

different weather conditions was not as important

as the amount of canopy cover provided by the

specific roost tree.

Results from this study also suggest that the

structural diversity within a site is important, given

Table 3. Correlation rc.sults from comparisons of perch height and temperature on days with and without precipi-

tation.

Site

No PrECIEI J AI ION PRKCtEITAlION

r-VAt.t.iE P-VAITIE r-VAt.UE P-VAl.UE

Yarra Valley Metropolitan Park -0.80 <0.001* -0.03 0.875

Warrandyte -0.27 0.021* 0.06 0.714

One Tree Hill -0.87 <0.001* -0.06 0.065

Smiths Gully -0.68 <0.001* -0.39 0.006*

Steels Greek -0.45 <0.001* 0.62 <0.001*

Toolangi -0.59 <0.001* -0.18 0.112

* Represents a significant relationship between perch height and temperature.

December 2002 The Powerful Owl in Urban Environments 299

that the Powerful Owls may use trees of different

heights to regulate their temperature in relation to

climatic conditions. Unfortunately environmental

change accompanying urbanization often results in

less structural diversity in vegetation, which can

mean that Powerful Owls have less choice in suit-

able thermal environments. What effect loss of

structure will have on survival and reproduction is

largely unknown, but it may in part explain why

the Powerful Owl is rarely found in highly-urban-

ized areas.

This information is important for future man-

agement of the Powerful Owl because it suggests

that this species does not simply move to higher or

lower branches in the one tree; rather, it moves to

an alternative roost tree with more suitable struc-

tural characteristics when it changes heights.

Therefore, management of the vegetation in the

urban areas must ensure that there is structural

diversity in the vegetation. Currently, the focus of

vegetation management for the Powerful Owl has

been on maintaining old eucalypts (canopy layer)

.

However, this may not provide for the structural

resource requirements of this species. Vegetation

management for the Powerful Owls should, there-

fore, be expanded to include the obviously impor-

tant mid-story species such as Acacia and Leptosper-

mum.

Acknowledgments

We thank Alan Webster for his on-site help, particularly

for providing historical records, and for continual sup-

port and other assistance. We also thank the Holsworth

Wildlife Research Fund, the M.A. Ingram Trust, Birds

Australia, and Deakin University for providing financial

support. We also wish to acknowledge the constructive

suggestions provided by referees of this manuscript.

Literature cited

Cooke, R., R. Wallis, A. Webster, and J. Wilson. 1997.

Diet of a family of Powerful Owls Ninox strenua from

Warrandyte, Victoria. Proc. R. Soc. Vic. 107:1—6.

, R. Wallis, and A. Webster. 2002. Urbanization

and the ecology of Powerful Owls Ninox strenua in out-

er Melbourne, Victoria. Pages 100-106 in I. Newton,

R. Kavanagh, J. Olsen, and I. Taylor [Eds.], Ecology

and conservation of owls. CSIRO Publishing, Mel-

bourne, Australia.

Debus, S.J.S. and C.J. Chafer. 1994. The Powerful Owl

Ninox strenua in New South Wales. Aust. Birds (Sup-

plement) 28:20-38.

Department of Natural Resources and Environment,

Victoria, 1999. Powerful Owl Ninox strenua. Flora and

fauna guarantee act. Department of Natural Resourc-

es and Environment, Melbourne, Australia.

Fleay, D. 1968. Nightwatchmen of bush and plain. Jaca-

randa Press, Brisbane, Australia.

Garnett, S.T and G.M. Crowity. 2000. The action plan

for Australian birds. Canberra: Environment Austra-

lia, Australian Government. Canberra, Australia.

Higgins, PJ- 1999. Handbook of Australian, New Zealand

and Antarctic birds. Vol. 4. Oxford Univ. Press, Mel-

bourne, Australia.

Kavanagh, R.P. and K.L. Bamkin. 1994. Distribution of

nocturnal forest birds and mammals in relation to the

logging mosaic in south-eastern New South Wales

Biol. Conserv. 71:41-53.

Mansergh, I.C., C. Beardsell, S. Bennett, R. Brereton,

K. O’Conner, K. Sandiford, and M. Schulz. 1989.

Report on the sites of zoological significance in the

Upper Yarra Valley (western section) and Dandenong

Ranges. Arthur Rylah Institute for Environmental Re-

search, Tech. Rep. Ser. No. 90, Melbourne, Australia

Pavey, C.R. 1995. Food of the Powerful Owl Ninox strenua

in suburban Brisbane, Queensland. Emu 95:231-232.

, A.K. Smyth, and J. Mathieson. 1994. The breed-

ing season diet of the Powerful Owl Ninox strenua at

Brisbane, Queensland. Emu 94:278-284.

Roberts, G.J. 1977. Birds and conservation in Queens-

land. Sunbird 8:73—82.

Rose, A.B. 1993. Notes on the Powerful Owl Ninox strenua

in New South Wales. Aust. Birds 26:134—136.

Seebeck, J.H. 1976. The diet of the Powerful Owl Ninox

strenua in western Victoria. Emu 76:167-170.

Webster, A., R. Cooke, G. Jameson, and R. Wallis. 1999

Diet, roosts, and breeding of Powerful Owls Ninox

strenua in a disturbed, urban environment: a case for

cannibalism? Or a case for infanticide? Emu 99:80—83.

Received 31 December 2001; accepted 7 August 2002

/ Raptor Res. 36(4) :300-308


NEST-SITE SELECTION OF THE CROWNED HAWK-EAGLE IN THEFORESTS OF KWAZULU-NATAL, SOUTH AFRICA,

AND TAI, IVORY COAST

Gerard Malan^School of Life and Environmental Sciences, University ofDurban-Westville, PB X5400f Durban 4000, South Africa

SusANNE ShultzPopulation and Evolutionary Biology Research Group, School of Biology, Nicholson Building, University of Liverpool,

Liverpool L69 3 GS, United Kingdom

Abstract.—Structural characteristics of Crowned Hawk-Eagle {Stephanoaetus coronatus) nest sites were

compared between forests in KwaZulu-Natal province, South Africa, and the Tai National Park, Ivory

Coast, and key features of nesting trees and nest-placement sites were identified. Nest-tree heights and

nest heights differed appreciably between three tree groups with the highest being indigenous Tai trees

(x tree height = 52 m and x nest height = 36 m, N = 8 nests), followed by exotic eucalyptus (x = 44

and 22 m respectively, N = 10) and indigenous trees (x = 24 and 14 m respectively, N = 17) from

KwaZulu-Natal. All the nest trees in Tai were eraergents, whereas 11 of 17 indigenous nest trees and

only two of 10 eucalyptus were so in KwaZulu-Natal. Non-emergent eucalyptus nest trees were predom-

inantly edge trees that may have provided easier access for flying eagles. Overall, nest forks were moreaccessible for flying eagles than random forks, although access did not differ between nests located in

emergent and non-emergent trees. Crowned Hawk-Eagles transport long sticks and heavy prey items to

their nests and access was probably the most critical feature of both the nest tree and placement of the

nest. Wildlife managers must, therefore, ensure that lone-standing or emergent trees are cultivated and

conserved, and flight paths to nests are kept open to allow Crowned Hawk-Eagles continued and easy

access to their nests.

Key Words: Crowned Hawk-Eagle, Stephanoaetus coronatus; nest access; emergent trees; nest-site selection;

wildlife management.

SELECCION DEL SITIO NIDO DEL AGUILA CORONADA EN LOS BOSQUES DE KWAZULU-NATAL,SUR AFRICA, Y TAI, COSTA DE MARFIL

Resumen.—Las caracteristicas estructurales de los sitios nido de las aguilas coronadas {Stephanoaetus

coronatus) fueron comparadas entre los bosques de la provincia KwaZulu-Natal, Sur Africa, y el parque

nacional Tai, Costa de Marfil, y se identilicaron los rasgos claves de los arboles nido y de los sitios de

ubicacidn de los nidos. Las alturas de los arboles nido y las alturas de los nidos difirieron apreciable-

mente entre arbol y grupo de arboles siendo los mas altos los nativos Tai (x altura del arbol = 52 m yX altura del nido = 36 m, N = 8 nidos), seguido por eucaliptos exoticos (x = 44 y 22 m respectivamente,

N ~ 10) y arboles nativos (x = 24 y 14 m respectivamente, N = 17) de KwaZulu-Natal. Los arboles nido

de eucaliptos no emergen tes fueron predominantemente arbcdes de borde que podian proveer mas

facil acceso a las aguilas en vuelo. En conjunto, las horquelas en nidos fueron mas accesibles para las

aguilas que horquetas colocadas al azar, aunque el acceso no dilirio entre los nidos colocados en arboles

emergentes y no emergentes. Las aguilas coronadas transportan grandes ramas y presas pesadas a sus

nidos y probablementc el acceso fue el rasgo mas critico tanto para la seleccion del arbol nido comopara la ubicacion del nido. Los manejadores de vida silvestre deben, por lo tanto, asegurar que arboles

aislados o emergentes son cultivados y conservados, y que las vias de vuelo a esos nidos permaneceran

abiertas para permitir a las aguilas coronadas continuo y facil acceso a sus nidos.

[Traduccion de (iesar Marquez]

Tree-nesting raptors select nesting trees and nest

sites on the basis of certain structural features that

^ Present address: Department of Nature Conservation,

Pretoria Technikon, P.B. X680, Pretoria 0001, South Af-

rica; e-mail address: [email protected]

hide the nest from potential predators, insulate the

nest against adverse weather conditions, place the

birds close to their hunting habitats and allow

them easy access to the nest (Moore and Henny

1983, Speiser and Bosakowski 1987, Lilieholm et

al. 1993, Burton et al. 1994, Selas 1996, Malan and

300

December 2002 Nest-seee Selection oe the Crowned Hawk-Eagle 301

Robinson 2001). Larger raptors often nest in an

exposed position that allows easy access to and

from the nest to deliver long sticks and heavy prey

(Speiser and Bosakowski 1987, Burton et al. 1994).

To further facilitate access, large raptors nest in tall

emergent trees or large trees with open branch

structures that respectively allow them access to the

nest both above and within the canopy (Moore and

Henny 1983, Burton et al. 1994, Malan and Rob-

inson 2001). Unfortunately, these preferences

bring large eagles in direct conflict with man as

large trees often are selectively harvested for com-

mercial and subsistence purposes (Bijleveld 1974,

Watson and Rabarisoa 2000).

In the predominantly arid South Africa, the de-

pletion of indigenous forest habitats and the arriv-

al of commercial exotic Eucalyptus, Pinus, Acacia,

and Populus trees have had a mixed impact on the

abundance and distribution of tree-nesting forest

birds (Low and Rebelo 1996, Allan et al. 1997).

Although by 1997 the area under commercial pulp-

wood and sawlog plantations (15 186 km^) was four

times larger than the existing natural forests (Van

der Zel 1996, Anon. 1998), the very short rotation

intervals of plantations (8-16 yr) do not allow the

trees to attain the size necessary to support large

stick nests. However, isolated, non-commercial

stands of large exotic trees are used for nesting by

indigenous birds, including raptors (Steyn 1977,

Macdonald 1986, Malan and Robinson 2001). In

indigenous forests, the processes of deforestation,

forest fragmentation, and the selective removal of

big trees from remnant patches alter the size, struc-

ture, and availability of indigenous trees for nest-

ing (Tarboton and Allan 1984, Allan and Tarboton

1985, Seydack 1995, Vermeulen 1999).

In South Africa, the Crowned Hawk-Eagle {Ste-

phanoaetus coronatus) has recently become of for-

mal conservation concern and the status of the

species has changed to near threatened due to the

loss of its previously suitable, indigenous nesting

habitat to short rotation, exotic plantations

(Barnes 2000) . Throughout much of its range, the

Crowned Hawk-Eagle breeds in tall evergreen for-

ests but can also nest in deciduous forests and

woodland-forest mosaics (Tarboton and Allan

1984). These birds prefer large forest trees for

nesting and the nest is usually situated in a major

fork, 8-30 m above ground but can be as high as

46 m (Steyn 1982, Tarboton and Allan 1984, Brownand Amadon 1989). In South Africa, CrownedHawk-Eagles nest in exotic eucalyptus and pines,

in addition to indigenous trees, consisting of most-

ly White Stinkwoods ( Celtis africana) (Tarboton andAllan 1984, Boshoff 1988).

The objective of this study was to compare

Crowned Hawk-Eagle nesting sites in three tree

groups and to use this information to provide re-

source managers with silvicultural guidelines for

providing nest-placement sites and stands for

Crowned Hawk-Eagles. As the forests in the

KwaZulu-Natal province. South Africa, are relative-

ly small in size and patehy in distribution (Boshoff

1997, Midgley et al. 1997), nest site characteristics

of these forests were compared with those from the

extensive and continuous, indigenous forest of the

Tai National Park, Ivory Coast. These comparisons

clarify which structural features are most important

when selecting a nest site, and how flexible

Crowned Hawk-Eagles are with regard to these

characteristics. Second, for KwaZulu-Natal, we ex-

amine stand size to determine the minimal habitat

requirements and compare topographical features

with randomly-selected sites to determine the ea-

gle’s selectivity for these features.

Study Areas

In South Africa, Crowned Hawk-Eagle nest sites werelocated for study during forest surveys in the KwaZulu-Natal (29°S, 31°E). Indigenous tree stands were surveyed

in forests characterized by a 10-25 m high canopy, dis-

tinct vegetation strata and numerous dominant tree spe-

cies (Low and Rebelo 1996, Midgley et al. 1997). Themean annual rainfall in these forests range from 900-1500 mm. Indigenous nest trees were sampled in the Or-

ibi Gorge, Vernon Crookes, Krantzkloof, Harold John-son, and Dlinza Eorest nature reserves, Ithala GameReserve, Hluhluwe-Umfolozi Park, all areas managed by

the KwaZulu-Natal Wildlife, and the Umgeni Valley Na-

ture Reserve and Tanglewood Natural Heritage Site. Ex-

otic eucalyptus were surveyed in abandoned plantations,

self-sown stands, and planted trees in large domestic gar-

dens, but none were known from commercial sawlog or

pulpwood plantations.

In the Ivory Coast, all nest sites were located within a

50 km^ area around the Station de la Recherche en Ecol-

ogie Tropicale (SRET, 7°00'N, 5°50'W) near the western

edge of the park. The Tai National Park is the largest

continuous lowland forest in West Africa (454 000 ha)

and contains the last sizeable protected habitat for a

number of Upper Guinea Forest endemics (Gartshore et

al. 1995). The mean annual rainfall at the research sta-

tion is 1800 mm. The forest was selectively logged in the

early 1970s, but the structure is essentially indistinguish-

able from a primary forest. The main forest canopy is

30-40 m in height, with emergent trees reaching to over

60 m (Guillaumet 1994).

Methods

The authors and conservation ofhcers located 27

Growned Hawk-Eagle nests in KwaZulu-Natal and eight

302 Malan and Shultz VoL. 36, No. 4

m Tai. Of the nests in KwaZulu-Natal, 19 were found by

listening for the loud queee-queee soliciting calls of nest-

lings or by spotting large nests (Steyn 1982). Althoughthis non-systematic search method may bias the sample

toward accessible and conspicuous nests (Daw et al.

1998), the nest-site data include nests from a wide selec-

tion of forest and nest-tree types. Sampled nest trees werelocated in indigenous forests, exotic monocultures, andmixed forests, and nest tree species were grouped into

either indigenous or eucalyptus stands.

The following nest-tree characteristics were recorded

from each nest site: the tree diameter at breast height

(14 m, DBH) of all stems >22 cm in diameter; tree

height (T), nest height (N), height of the first foliage,

and the height of the first side branch (R, irrespective if

It was dead or alive) . All height measurements were taken

with a clinometer. For trees with buttresses {N =3), the

circumference of the tree, including the buttresses, was

measured at breast height, a diameter calculated and di-

vided by two as to provide a conservative estimate of

DBH. The percent nest height was the proportional dis-

tance the nest was placed from the top of the tree ((N/

T)100) and the percent first branch height was the pro-

portional height the first branch was placed from the top

of the tree ((R/T)100).

Nests were classified as being placed within or belowthe foliage. Each nest was scored as either being posi-

tioned in a main fork, against the main branch (i.e., pri-

mary axis, mainly vertical), or on a side branch (i.e., sec-

ondary axes, mainly horizontal). The number of

branches supporting the nest was also counted. Lastly,

the nest tree was classified as emergent if the branch andfoliage structure protruded above the surrounding for-

est.

For each nest tree, we identified large and open forks,

excluding the nest fork, which could possibly support a

Crowned Hawk-Eagle nest that was 2 m wide and 2.5 mdeep (Steyn 1982). Each of these forks was categorized

as being positioned in a central fork or crotch (i.e., be-

tween main branches), as against the main branch, or ona side branch, and numbered from tree bottom to top.

A random fork was selected from the category of the fork

that supported the nest (i.e., if the nest was against a

main branch, the random fork was selected from similar

forks). If the random fork was not available from the

category that supported the nest, it was selected from a

combined sample of the remaining two positions.

For each cardinal direction (N, E, S, and W), accessi-

bility of the nests and random forks were determined by

whether the flying eagle would have a 30 m unobstructed

approach on a horizontal plane. For a flying eagle, a

flight path to the nest obstructed by foliage and/orbranches thus qualified inaccessibility.

We sampled characteristics of the three trees closest to

the nest tree. The distance from the nest tree to each

surrounding tree was measured. We calculated the meanarea occupied by the trees by squaring the mean distance

of the three trees from the nest tree. We then converted

the result to the number of trees per hectare and cal-

culated a tree density estimate at the nest tree (Phillips

1959).

For KwaZulu-Natal nest trees, each nest was plotted ona 1:10 000 orthophoto (black and white aerial photo-

graph with 50 m contour lines) to calculate stand size

and shape. From this photo, the maximum length (A)

and maximum width (B; perpendicular to the maximumlength axis) of the nest stand was measured. All mea-surements from 1:10 000 orthophotos were rounded to

10 m to allow for a 1 mm measurement error. Stand

shape (S) was defined as the maximum stand width di-

vided by the maximum length, with values ranging fromone (square shape) to zero (elongated shape). Nest stand

shapes were grouped into square (Shape ^0.5) or elon-

gated (Shape <0.5). The surface area of planted forests

was calculated from orthophotos by measuring the stand

lengths and widths. The surface area of indigenous forest

stands could not be calculated from orthophotos because

the edges of indigenous forests were not defined clearly

and the surface area was, therefore, estimated as S = (A/2)(B/2)(tt). From the orthophotos, the nest trees werealso categorized as being located on the edge of the stand

(i.e., the first tree encountered on the edge of a forest

stand). Lastly, distances to water, road, and nearest hu-

man habitation were measured from the nest tree andone random tree selected from each nest stand.

All data were subjected to the Kolmogorov-Smirnovone-sample test of normality. If the distribution of the

data was found to be non-normal, the non-parametric

Kruskal-Wallis test or Mann-Whitney Latest was employedThe Tukey honest significant difference test for unequalsample sizes was employed to determine which groups

are particularly different from each other after a signifi-

cant Kruskal-Wallis test was obtained from the Analysis of

Variance. The Pearson’s Chi-square test was used to test

for patterns with categorical variables. All data were an-

alyzed using the Statistica software package (StatSoft

1995) and probability levels were set at a = 0.05.

Results

Of the 35 Crowned Hawk-Eagle nests analyzed,

10 were located in eucalyptus and 17 in indigenous

trees in KwaZulu-Natal, and eight in indigenous

trees in Tai. Indigenous nest trees identified in

KwaZulu-Natal included Ficus spp. (7), Chrysophyl-

lum viridifolium (3), Syzygium cordatum (2), Cussonia

spicala, Scholia brachypetala, and Celtis africana. Theexotic nest trees were all eucalyptus. Nest trees

identified in Tai included Lofira alata, Klainodoxa

gabonesis, Ceiba pentandra, and Alstonia boonei.

All tree characteristics measured differed amongthe three tree groups (Table 1). Tai and eucalyptus

nest trees were taller than KwaZulu-Natal’s indige-

nous trees. Tai nest trees were larger in diameter,

and had higher first foliage, side branches and per-

cent first side branch heights than trees from

KwaZulu-Natal. Nest heights differed among all

three tree groups, and the percent nest heights

were lower in eucalyptus than Tai nests (Table 1).

The number of branches that supported nests

did not differ among tree groups (Kruskal-Wallis

2,35 ~ 1.7, P = 0.41), and the eagles used on av-

December 2002 Nest-site Sei.ection c:>f i he Crowned Hawk-Eagee 303

Table 1. Crowned Hawk-Eagle nest-tree characteristics of eucalyptus and indigenous tree groups in KwaZulu-Natal

and Tai. Means ± one standard deviation and range in parenthesis. Values with the same superscripts indicate values

that differed significantly from each other in the three-way comparison.

Species Ciass

Indigenous

KwaZui.u-Natal

Eucai.yptus

RWAZuriJ-NAIAL

Indigenous

Tai NKruskal-

Wallis HDBH (cm) 93^' ± 29 126*> ± 32 234^'^ ± 66 35 21.6**

(40-151) (83-206) (167-344)

Tree height (m) 24ab + 5 44a + g 52'^ ± 14 35 25.7**

(T5-34) (34-54) (33-67)

Height of hrst 9“’ ± 6 12*’ ± 9 33^>'> ± 7 35 17.8**

foliage (m) (1-19) (6-27) (26-42)

Height of first side 9“ ± 6 15'’ ± 7 34’’ ± 9 35 17.8**

branch (m) (1-20) (6-25) (25-47)

Nest height (m) ]4ab + 3 22a<: + 7 ± 10 35 23.4**

(7-21) (13-35) (2.5-49)

Percent nest height 58 ± 14 52^' ± 13 71" ± 13 35 7.6*

(43-93) (36-67) (44-90)

Percent first side 36^' ± 21 32b2: 12 66"’’ ± 13 35

branch height (4-62) (16-47) (44-78)

^ihc = p <; 0.05, I'ukey tests.

* P < 0.05.

P < 0.001.

erage 3 ± 1 branches (A ± SD, N = 35 trees) to

nest on. Twenty-seven of 32 nests (84%) were

placed within the foliage (as opposed to under the

foliage), and placement of nests in relation to the

foliage was not associated with tree groups (x^

0.7, P = 0.70). In Tai, 63% of the nests {N = 8)

were placed on the lowest side branch, more fre-

quently than nests in indigenous (13%, N — \1)

and eucalyptus trees in KwaZulu-Natal (10%, N =

10, = 9.3, P< 0.01).

Of the 35 nests sampled, 20 (57%) were placed

m a central fork, nine (26%) on a side branch, and

six (17%) against the main branch; nest placement

was not associated with tree groups (x^ = 6.3; P —

0.17). Whereas seven (78%) of the nine side-

branch nests and four (67%) of the six main-

branch nests were from the most abundant fork

category, 18 (90%) of the 20 central-crotch nests

Table 2. The emergence of Crowned Hawk-Eagle nest

trees above the surrounding forest.

Emergent Nest Trees Yes No Totai.

Indigenous—KwaZulu-Natal 11 6 17

Eucalyptus—KwaZulu-Natal 2 8 10

Indigenous—Tai 8 0 8

Total (Percent) 21 (60) 14 (40) 35

were from trees where this fork type was not the

most abundant (x^ = 6.3; P < 0.001). Overall, 22

(63%) of the 35 nests were not placed in the most

abundant fork category and nest placement could

not be associated with the most abundant fork cat-

egory of the different tree groups (x'^ 1.0; P =

0.59).

The number of forks per nest tree did not differ

among the tree groups (1 1 ± 6 forks in indigenous

KwaZulu-Natal trees, 14 ± 8 in eucalyptus, and 7

± 3 in Tai nest trees; Kruskal-Wallis ~ ^-4? P= 0.16). Whereas the number of central forks per

tree did not differ among tree groups (1 ± 1, Krus-

kal-Wallis 772,35 = 3.2, P = 0.21), the number of

side forks did (indigenous KwaZulu-Natal 5 ± 4

forks, eucalyptus 2 ± 2, and indigenous Tai 3 ± 3;

Kruskal-Wallis 772 35 = 6.2, P< 0.05), although the

classes were not significantly different from each

other (Tukey tests, all P > 0.05). Eucalyptus had

more forks against the main branch (11 ± 8) than

indigenous trees in KwaZulu-Natal (4 ± 3) and Tai

(3 ± 1; Kruskal-Wallis = 9.6, P< 0.01; Tukey

tests, all P < 0.05)

.

All the nest trees in Tai and 11 of 17 indigenous

nest trees in KwaZulu-Natal were emergents,

whereas only two of 10 eucalyptus protruded above

the forest canopy (x^ = 12.2, P < 0.05; Table 2).

Overall, nests were more accessible to flying eagles

304 Malan and Shultz VoL. 36, No. 4

Table 3. The number of Crowned Hawk-Eagle nest

trees, with flight paths sampled in four cardinal direc-

tions, which allowed access to nest and random forks for

17 indigenous and 10 eucalyptus trees in KwaZulu-Natal,

and eight indigenous trees in the Tai Forest.

Number of

Flight Paths None One Two Three Four x^

Nest fork 0 1 12 12 10

Random fork 4 12 8 4 7 18.6**

** p< 0.001.

than were random forks (Table 3) . Access to nests

could not be associated with their placement above

(as emergents) or within the forest canopy (Table

4) . In KwaZulu-Natal, seven of the eight non-emer-

gent eucalyptus were located on the edge of the

nest stand, whereas, all the non-emergent indige-

nous trees were located inside the nest stands (x^

= 7.3, P< 0.01).

The mean distance from the nest tree to the

nearest three trees did not differ among tree

groups (indigenous KwaZulu-Natal 11 ± 6 m, eu-

calyptus 12 ± 8 m, and indigenous Tai' 13 ± 5 m;

Kruskal-Wallis 7^2,34 ~ 1-0, P = 0.62). The density

of trees at nest sites also did not differ among tree

groups (all trees 156 ± 175 trees/ha, indigenous

KwaZulu-Natal 172 ± 183 trees/ha, eucalyptus 189

±219 trees/ha, and indigenous Tai 85 ± 62 trees/

ha; Kruskal-Wallis 7^2,34 ^ 1-0, P = 0.62).

The areas of 1 3 Crowned Hawk-Eagle nest stands

in KwaZulu-Natal were not normally distributed

and were predominantly less than 50 ha in size (Ta-

ble 5). Nest stands were primarily small (20 m in

width and 30-50 m in length) and elongated in

shape (shape-index <0.5; Table 5). Sbape-index

values could not be associated with eucalyptus andindigenous tree stands (x^ = 0.12, P = 0.73).

Table 4. The number of flight path.s per CrownedHawk-Eagle nest tree, sampled in four directions, which

allowed access to nest forks in emergent and non-emer-

gent trees.

Number of

Flight Paths None One Two Three Four Total

Emergent 0 0 5 7 9 21

Non-emergent 0 1 5 3 5 14 2.4

Nest and random tree distances to topographical

features were not different for all variables whencomparing means (Table 6) and Crowned Hawk-Eagles were, therefore, non-selective regarding

these topographical features. One tree selected for

nesting was 20 m from an inhabited brick house

and another 10 m from a used bitumen road.

Discussion

Nest-site Selection. Tree-nesting raptors assess

variables such as vulnerability to predators, protec-

tion against adverse weather conditions, the cost of

nest building, structural features of the nest tree,

and access to the nest when selecting a site to build

their nest (Newton 1979, Moore and Henny 1983,

Bosakowski and Speiser 1994, Burton et al. 1994).

Whilst smaller raptors regularly conceal their nests

to avoid predation, larger raptors are less secretive

and customarily put their nests in exposed posi-

tions (Speiser and Bosakowski 1987, Selas 1996).

The large, 2-2.5 m wide and 2.5-3 m deep nests

of the Crowned Hawk-Eagle (Steyn 1982) are very

conspicuous.

Although large raptors generally do not hide

their nests as they can defend their nestling against

predators (Moore and Henny 1983), CrownedHawk-Eagles do suffer some nest predation fromprimates, especially if the nest tree can be accessed

Table 5. Statistical distribution of KwaZulu-Natal Crowned Hawk-Eagle nest-stand variables and shape index with

the Kolmogorov-Smirnov distribution test (K-S d) for normality.

DominantCafegory(Percent) Mean ± 1 SD Range N K-S d

Surface area (ha) 0-50 (77) 35.4 ± 73.7 0.05-250.15 13 0.42*

Maximum width (m) 20 (69) 253 ± 363 20-1090 13 0.34

Maximum length (m) 30-50 (69) 759 ± 987 30-3520 13 0.32

Shape (0.0-1.0) 0.2-0.3 (23) 0.39 ± 0.22 0.04-0.80 13 0.16

* P < 0.0.5.

December 2002 Nest-site Selection of the Crowned Hawk-Eagle 305

Table 6. Topographical characteristics measured from Crowned Hawk-Eagle nest and random trees in KwaZulu-

Natal {N = 13 nests).

Variables Nest Tree Random Tree

Distance to water (m) 83 ± 147 (10-550)^^ 159 ± 199 (10-520) 0.86

Distance to house (m) 859 ± 1661 (20-6250) 906 ± 1738 (20-6550) 0.24

Distance to road (m) 282 ± 277 (10-810) 285 ± 341 (30-1010) 0.11

* Mann-Whitney fTtest.

^ Mean ± 1 SD (range).

from nearby trees (Tuer and Tuer 1974, Kalina and

Butynski 1994) . This may be a reason why CrownedHawk-Eagles often select emergents for nest sites,

especially in Tai where eight diurnal monkey spe-

cies are found at very high densities (McGraw

1998). In Tai, the tall nest trees with their wide

bases and high, first side branches (mean = 34 mfrom the ground) may be extremely difficult, if not

impossible, for monkeys to climb (T. Struhsaker

pers. comm.). In KwaZulu-Natal, the presence of

fewer primate species (three at the most; Smithers

1983) may have resulted in reduced predation risk

for nestlings and might have allowed for the use

of lower and non-emergent trees.

Sites may also be selected for nesting because

the foliage protects the nest against adverse weath-

er conditions (Moore and Henny 1983, Bosakowski

and Speiser 1994). Crowned Hawk-Eagle nests are

usually situated within the leafy canopy, but the

birds also nest in exposed positions in partially col-

lapsed or dead trees (Steyn 1982, Tarboton and

Allan 1984, Kalina and Butynski 1994). In this

study, 32 nests were located in or below the foliage

and therefore sheltered, whereas the remaining

three nests, two of which produced young during

the study, were located in exposed positions in

dead trees. Hence, although there was a trend for

the birds to nest in a sheltered position, other fac-

tors, such as the availability of suitable nesting sites

and the cost of building a new nest, probably in-

fluenced the continued occupation of a nest in a

dying or dead tree.

Lastly, tree-nesting forest raptors may select trees

for their size and structural features, such as a tall

and open canopy, that allow unobstructed access

to the nest (Speiser and Bosakowski 1987, Cerasoli

and Penteriani 1996). The Crowned Hawk-Eagle

may require a nest that is easily accessible as it

needs to fly to the nest carrying sticks up to 1.2 mlong and 8 cm thick (Steyn 1982). In addition.

Crowned Hawk-Eagles are capable of killing prey

3-4 times their body mass, such as bushbuck( Tra-

gelaphus scriptus; Daneel 1979), which they dismem-

ber and carry in parts to the nest. Brown (1966)

noted that, in the Karen Forest in Kenya, these ap-

proach flights were always above the canopy, very

laborious and broken into short 91-137 m stints so

as to rest between flights. Under these conditions,

access to the nest would be critical in order to de-

liver nesting material and prey to the nest. Nesting

above the forest canopy in an emergent tree en-

hances accessibility.

The large indigenous nest trees were simple in

structure and provided, on average, one central

fork, 3-4 forks against the main branch and 3-5

forks on side branches for the eagles to place their

nest. Notwithstanding, only 2-4 branches were

used on which to build these large nests, indicating

that big, primary and secondary forks were select-

ed and not the smaller, multi-stemmed forks from

within the canopy structure. Large raptors require

a large tree-fork (crotch) to place the nest in andthe more open branch structure may facilitate ac-

cess (Newton 1979). The exotic eucalyptus differed

from the indigenous nest trees in that they provid-

ed, on average, 1 1 more forks. This was largely due

to the single main-stem growth form of these com-

mercially-cultivated trees. Trees from these stands

were also largely of similar height, probably be-

cause trees in these single species stands were

planted simultaneously. As seven of eight non-

emergent, eucalyptus nest trees were located onthe edge of the nest stand, the eagles may circum-

vent the scarcity of emergent eucalyptus by select-

ing edge trees that have greater access to the nest.

In conclusion, because nests located within andabove the canopy were equally accessible, access

seemed to be the most critical feature identifying

a Crowned Hawk-Eagle nesting tree and site. Thefindings that indigenous nest trees in KwaZulu-Na-

tal did not differ from eucalyptus or indigenous

trees from Tai Forest in terms of tree density and

306 MaiAN AND Shui.tz VoL. 36, No. 4

central and side fork availability, may indicate that

indigenous trees with their multiple main stems

and open branch structure may be as accessible for

flying eagles as emergent or edge trees.

This study did not quantify the ‘openness’ and

accessibility of indigenous nest trees in KwaZulu-

Natal, particularly with regard to tree canopy di-

ameter and volume, branch spacing and diameter,

and branch angle as nests were often placed on

near horizontal branches. Also, we did not exam-

ine the inter-relationship between the largest-di-

ameter side branches (required to support the

large nests) and the position of the primary and

secondary forks below or just inside the foliage,

related to openness and improved access. We also

did not take into account the slope at the nest site

and aspect of the nest, as nests located on the

downhill side of the tree may have been more ac-

cessible to flying eagles. Given the floristic differ-

ences between forests in Tai and KwaZulu-Natal, a

comparison of nest sites Avith randomly selected

sites, conducted at each nest stand, would have fur-

ther contributed toward the understanding ofwhat

constitutes a suitable nest tree. Lastly, data on howeasy arboreal primates can climb nest trees, partic-

ularly from the base, would have added to our un-

derstanding of how successful Crowned Hawk-Ea-

gles are in eliminating the predation risk by

nesting in tall, emergent trees.

Recommendations. Wildlife managers need to

manage forests by balancing timber harvesting

with maintaining wildlife habitat and must employ

multi-resource plans to do so (Lilieholm et al.

1993, Vermeulen 1999, Malan and Robinson

2001). These plans should incorporate both prac-

tical and proactive management objectives to con-

serve nesting habitat for large eagles in exotic and

indigenous forests. Apart from silvicultural guide-

lines, other considerations must include the prox-

imity of nests to hunting habitat, their temporal

and spatial distribution, and tbe effects of humandisturbance on nesting eagles (Lilieholm et al.

1993).

In this study, because we could not obtain reli-

able data on the age of the nests and how manyyoung were fledged from each nest over time, wedid not compare the structural features of produc-

tive between unproductive nests. Although other

factors also influence productivity, e.g., experience

of breeders, prey abundance, and persecution

rates, the productivity analysis may have highlight-

ed subtle differences between suitable and unsuit-

able nest trees and nest-placement sites. Our rec-

ommendations should therefore be treated with

some caution, as nests included in this study might

have been found unsuitable on the long term be-

cause certain deficient nest features may have lim-

ited successful reproduction.

Nonetheless, the nest trees must have open-

branch structures and large tree-forks. As nest trees

are typically emergents or edge trees, these trees

can be cultivated by felling surrounding trees or

leaving the tall trees standing (Seydack 1995). In

this study more than half of the Crowned Hawk-

Eagle nests were positioned in a central fork, there-

fore, the techniques of coppice-reduction or selec-

tive pruning could be employed to cultivate a tree

with the preferred 2-4 main branches. As Brown

(1966) demonstrated, suitable nest trees can be

identified a priori, and managers can therefore im-

plement these techniques to ensure a continued

supply of suitable nest trees.

To qualify as a nest tree, commercial eucalyptus

should be managed to reach a minimum height of

34 m and DBH of 83 cm (i.e., minimum size se-

lected for nesting) . Indigenous trees selected must

attain a minimum height of 15 m and diameter of

35 cm. The mean stand density of 156 trees/ha can

be employed as a guideline for Crowned Hawk-Ea-

gle nesting habitat. Although exotic stands must be

managed to a minimum size so as not to encroach

onto indigenous vegetation, nest-tree stand size it-

self is nonessential. Furthermore, in plantations,

nest stands cannot be placed at random as raptors

often require nest trees to be located away from

certain topographical features (Andrew and Mosh-

er 1982, Malan and Robinson 1999). However, with

regard to the proximity of nests to human dwell-

ings, water bodies, and public roads, the CrownedHawk-Eagles of KwaZulu-Natal were remarkably

non-selective and tolerant. In fact, the city of Dur-

ban, located in this province, harbors 12 active

nests within its metropolitan boundaries. Inter-

stand distances were not recorded in this study, but

Crowned Hawk-Eagles are known to nest 1.8—4.0

km apart and, thus, require only a relatively small

patch of suitable hunting habitat (Tarboton and

Allan 1984, Allan et al. 1996, Mitani et al. 2001,

Shultz 2002). Given the size of some of the prey

these eagles hunt, nest stands must preferentially

be located near the hunting habitat so as to sbort-

en flight distances to the nest.

Because Crowned Hawk-Eagles use the samenest for 10 years or longer, often until the tree col-

December 2002 Nest-site Seitctton of the Crowned Hawk-Eagle 307

lapses (Brown 1966, Steyn 1982), suitable trees

should not be felled. If the nest stand or tree must

be harvested, the felling should be done outside

the birds’ breeding season (August-March) and 6-

12 months after the nestlings have fledged to allow

sufficient time for the young bird to become in-

dependent (Steyn 1982, Tarboton and Allan 1984).

Given that a nest takes 4-5 mo to build (Brown

1966), replacement nest trees, located in the vicin-

ity of the nest tree in use, should be cultivated long

in advance to provide a suitable alternative nest.

The Crowned Hawk-Eagle in South Africa has

been classified as near threatened because of past

exploitation of nest trees and the likely destruction

of nesting habitat in the near future (Boshoff et al.

1983, Barnes 2000). Occupied nests should be

closely monitored to assess the status of this species

and to collect data on what constitutes productive

nests. Large tree-nesting forest raptors will always

have few suitable trees to nest in as large trees and

forks are less abundant than smaller ones (Newton

1979). When nesting in large trees, eagles also

compete directly with humans for this scarce re-

source (Boshoff et al. 1983, Watson and Rabarisoa

2000). It is, therefore, no longer adequate simply

to protect forests for birds of conservation con-

cern, but specific efforts must be made to satisfy

the nesting requirements of the Crowned Hawk-

Eagle and other tree-nesting forest raptors; e.g., in

South Africa the Bat Hawk {Macheiramphus alci-

nus), Ayres’s Hawk-Eagle (Hieraaetus ayresii), and

Fasciated Snake-Eagle {Circaetus fasciolatus)

(Barnes 2000, Malan and Marais in press). Ulti-

mately, a species-specific management plan should

be developed for these and other tree-nesting for-

est birds and the maintenance of nest-tree struc-

tural and topographical features incorporated into

management decisions.

Acknowledgments

We want to thank Natal Portland Cement and the

KwaZulu-Natal Ornithological Trust for sponsoring this

project. We also thank KwaZulu-Natal Wildlife for allow-

ing us to work in their reserves and park. Bill Howells

and David Johnson were particularly helpful in locating

nest sites. Guy Tedder, Denise James, Martin Buchler,

Gavin Lorry, and Bill Walker also informed us of nesting

localities. In Tai, we thank Professor Ronald Noe for host-

ing the Crowned Hawk-Eagle project, the Centre Suisse

des Recherches Scientifiques, Centre de Recherche enEcologie, the Project Autonome pour la Conservation duParc National de Tai for logistical support, the Minstere

de la Recherche and the Direction de la Protection de la

Nature for permission to conduct the study. Funding (for

S. Shultz) was provided by the Raptor Research Foun-

dation, Inc., Leslie Brown Memorial Award, the Pere-

grine Foundation, a Wildlife Conservation Society Re-

search Fellowship, and the Leakey Foundation.

Literature Cited

At j an, D. and W.R. Tarboton. 1985. Sparrowhawks and

plantations. Pages 167-177 mL.J. Bunning [Ed.], Pro-

ceedings of the symposium on birds and man. Wits

Bird Club, Johannesburg, South Africa.

, D. Johnson, and T. Snyman. 1996. The crowned

eagles of Durban and Pietermaritzburg. Afr. Birds Bird-

ing 1:2-13.

, J.A. Harrison, R.A. Navarro, B.W. Van Wilgen,

AND M.W. Thompson. 1997. The impact of commer-

cial afforestation on bird populations in MpumalangaProvince, South Africa—insights from bird atlas data.

Biol. Conserv. 79:173-185.

Andrew, J.M. and J.A. Mosher. 1982. Bald Eagle nest-site

selection and nesting habitat in Maryland. J. Wildl

Manage. 46:383-390.

Anonymous. 1998. Commercial timber resources and

roundwood processing in South Africa 1996/1997.

Dept, of Water Affairs and Forestry, Pretoria, South

Africa.

Barnes, K.N. 2000. The eskom red data book of birds of

South Africa, Lesotho, and Swaziland. BirdLife South

Africa, Johannesburg, South Africa.

Bijleveld, M. 1974. Birds of prey of Europe. Macmillan

Press, London, UK.

Bosakowski, T. and R. Speiser. 1994. Macrohabitat selec-

tion by nesting Northern Goshawks: implications for

managing eastern forests. Pages 46—49 in W.M. Block,

M.L. Morrison, and M.H. Reiser [Eds.], The North-

ern Goshawk: ecology and management. Studies in

avian biology No. 16. Cooper Ornithological Society,

Sacramento, CA U.S.A.

Boshoff, A.F. 1988. The spacing and breeding periodic-

ity of Crowned Eagles in the southern Cape Province.

Bontebok 6:34—36.

. 1997. Crowned Eagle Stephanoaetus coronatus. Pag-

es 194—195 m J.A. Harrison, D.G. Allan, L.G. Under-

hill, M. Herremanns, A.J. Tree, V. Parker, and C.J.

Brown [Eds.], The atlas of southern African birds

Vol. 1. BirdLife, Johannesburg, South Africa.

, C.J. Vernon, and R.K. Brooke. 1983. Historical

atlas of the diurnal raptors of the Cape Province

(aves: falconiformes) . Ann. Cape Prov. Mus. Nat. Hist

14:173-297.

Brown, L.H. 1966. Observations on some Kenya eagles.

Ibis 108:531-572.

and D. Amadon. 1989. Eagles, hawks, and falcons

of the world. Wellfleet Press, New York, NY U.S.A.

Burton, A.M., R.A. t\lford, and J. Young. 1994. Repro-

ductive parameters of the Grey Goshawk {Accipiter no-

vaehollandiae) and Brown Goshawk {Accipiterfasciatus)

at Abergowrie, northern Queensland, Australia JZool. Land. 232:347—363.

308 Malan and Shuitz VoL. 36, No. 4

Cerasoli, M. and V. Penteriani, 1996. Nest-site and ae-

rial point selection by Common Buzzards {Buteo buteo)

in Central Italy. / Raptor Res. 30:130-135.

Daneel, A.B.C. 1979. Prey size and hunting methods of

the Crowned Eagle. Ostrich 50:120—121.

Daw, S.K., S. DeStefano, and R.J. Steidl. 1998. Does sur-

vey method bias the description of Northern Goshawk

nest-site structure? J. Wildl. Manage. 62:1379-1384.

Gartshore, M.E., P.D. Tayi or, and I.S. Erancis. 1995.

Forest birds in the Cote d’Ivoire: a survey of Tai Na-

tional Park and other forest and forestry plantations.

BirdLife Int. Stud. Rep. No. 58. BirdLife Internation-

al, Cambridge, U.K.

Guillaumet, J.L. 1994, La flore. Pages 66-71 m E.P. Rie-

zebos, A.P. Vooren, and J.L. Guillaumet [Eds.], Le

Parc National de Tai, Cote d’Ivoire. Synthese des con-

naissances. Fondation Tropenbos, Wageningen, Neth-

erlands.

Kalina, J. and T.M. Butynski. 1994. Natural deaths of two

Crowned Eagles in Uganda. Gator 9:28-31.

Lilieholm, R.J., W.B. Kessler, and K. Merrill. 1993.

Stand density index applied in timber and goshawk

habitat objectives in Douglas-Fir. Environ. Manage. 17:

773-779.

Low, A.B. and A.G. Rebei.o. 1996. Vegetation of South

Africa, Lesotho, and Swaziland. Dept, of Environmen-

tal Affairs and Tourism, Pretoria, South Africa.

Macdonaid, I.A.W. 1986. Do redbreasted sparrowhawks

belong in the Karoo? Bokmakierie 38:3-4.

Malan, G. and E.R. Robinson. 1999. The diet of the

Black Sparrowhawk: hunting columbids in man-al-

tered environments. Durban Mus. Novit. 24:43-47.

and E.R. Robinson. 2001. Nest-site selection by

Black Sparrowhawks Accipiter nielanoleucus: implica-

tions for managing exotic pulpwood and sawlog for-

ests in South Africa. Environ. Manage. 28:195-205.

AND A.V.N. Marais. 2002. Guidelines for the de-

sign and management of artificial raptor perches and

exotic nest-tree sites on forestry estates. S. Afr. For. /.:

in press.

McGraw, W.S. 1998. Comparative locomotion and habi-

tat use of six monkeys in the Tai Forest, Ivory Coast.

Am. ]. Phys. Anthropol. 105:493-510.

Midgley, J.J., R.M. Cowling, A.H.W Seydack, and (i.E

van Wyk. 1997. Forest. Pages 278-299 in R.M. C'.owl-

ing, D.M. Richardson, and S.M. Pierce [Eds.], Vtygc-

tation of southern Africa. Cambridge Univ. Press,

Cambridge, U.K.

Mitani, J.C., WJ. Sanders, J.S. Lwanga, and T.K.L. Wind-

eelder. 2001. Predatory behaviour of Crowned Hawk-

Eagles {Stephanoaetus coronatus) in Bibale National

Park, Uganda. Behav. Ecol. Sociobiol. 49:187-195.

Moore, K.R. and CJ. Henny. 1983. Nest-site character-

istics of three coexisting accipiter hawks in northeast-

ern Oregon. Raptor Res. 17:65-76.

Newton, I. 1979. Population ecology of raptors. T. & A.DPoyser, Berkhamsted, U.K.

Phillips, E.A. 1959. Methods of vegetation study. Holt,

Rinehart & Winston, Inc., New York, NY U.S.A.

Selas, V. 1996. Selection and reuse of nest stands by spar-

rowhawks {Accipiter nisus) in relation to natural andmanipulated variation in tree density, f. Avian Biol. 27.

56-62.

Sfydacr, A.H.W. 1995. An unconventional approach to

timber yield regulation for multi-aged, multispecies

forests. Fundamental consideration. For. Ecol. Manage77:139-153.

Shuitz, S, 2002. Population den.sity, breeding chronolo-

gy and diet of Crowned Eagles Stephanoaetus coronatus

in Tai National Park, Ivory Coast. Ibis 144:135-138.

Smithers, R.H.N. 1983. The mammals of the southern

African sub-region. University of Pretoria, Pretoria,

South Africa.

Spelser, R. and T. Bosakowski. 1987. Nest-site selection

by Northern Goshawks in northern New jersey andsoutheastern New York. Cowiior 89:387-394.

StatSoft. 1995. Statistica for Windows. StatSoft, Inc,

2300 East 14th Street, Tulsa, OK U.S.A.

Steyn, D.J, 1977. Occupation and the use of the eucalyp-

tus plantations in Tzaneen area by indigenous birds

N A/l For /. 100:56-60.

Steyn, P. 1982. Birds of prey of southern Africa. David

Philip Publishers, Cape Town, South Africa.

Tarboton, W.R. and D.G. Allan. 1984. The status andconservation of birds of prey in the Transvaal. Trans-

vaal Mus. Monogr. No. 3. Transvaal Museum, Pretoria,

South Africa.

Tler, V. and J. Tuer. 1974. (browned Eagles of the Ma-topos. Honeyguide 80:32-41.

Van der Zel, D.W. 1996. South African national forestry

action plan. Dept, of Water Affairs and Forestry, Pre-

toria, South Africa.

Vermeulen, C. 1999. The multiple-use management of

the indigenous evergreen high forests of the southern

Cape and Tsitsikamma. Dept, of Water Affairs andE'orestry, Knysna, South Africa.

Watson, R.T. and R. Rabarisoa. 2000. Sakalava fisher-

man and Madagascar Fish-F.agles: enhancing tradi-

tional conservation rules to control resource abuse

that threatens a key breeding area for an endangeredeagle. Ostrich 71:2-10.

Received 5 November 2001; accepted 2 August 2002


J.Raptor Res. 36(4):309-314


Juvenile Dispersal of Madagascar Fish-Eagles Tracked by Satellite Telemetry

Simon RafanomezantsoaThe Peregrine Fund, P.O. Box 4113, Antananarivo 101, Madagascar

Richard T. Watson ^ and Russell ThorstromThe Peregrine Fund, 5668 West Flying Hawk Lane, Boise, ID 83709 U.S.A.

Key Words: Madagascar Fish-Eagle, Haliaeetus vocifer-

oides; dispersal] satellite telemetry.

The Madagascar Fish-Eagle {Haliaeetus vociferoides) is

critically endangered (Stattersfield and Capper 2000)

with a small population limited to wetland habitats on

Madagascar’s western seaboard (Rabarisoa et al. 1997).

Observations of extra-pair adults at the nest and juveniles

m the territories of breeding pairs (Watson et al. 1996,

1999) suggest unusual behaviors that may occur as a re-

sult of overcrowding in limited suitable habitat, or if in-

nate, may reduce the species’ ability to disperse into un-

occupied habitat. In addition to the behavioral and

evolutionary significance of understanding these obser-

vations, the cause and consequence of this behavior mayaffect conservation interventions intended to prevent the

species’ extinction. We report the results of a pilot study

to measure the movements and habitat use of fledglings

after they left parental territories to better understand

post-fledging dispersal (Rafanomezantsoa 1998) and the

occurrence of extra birds at the nest, and to assess the

effect on dispersal of release of captive-raised birds (Wat-

son et al. 1996, 1999, Rafanomezantsoa and Kalavaha

1999).

The movements of raptors have been investigated for

decades mainly by banding, direct observation in limited

areas, or tracking using VHF radios (Meyburg and Mey-

burg 1999). Recently, satellite telemetry has provided a

method that makes possible the global location of birds

over an extended period. Satellite telemetry was consid-

ered the method of choice to study juvenile dispersal in

Madagascar Fish-Eagles which may reach maturity at 3-4

yr of age. In addition to the extended study period, ju-

veniles were expected to move distances greater than we

could follow with conventional VHE-radio telemetry be-

cause much of their range is inaccessible, especially dur-

ing Madagascar’s wet season when lowlands may flood

(Rafanomezantsoa 1997).

’ Corresponding author’s e-mail address: rwatson®

peregrinefund.org

Methods

This study occurred in coastal floodplain wetlands of

western Madagascar between the Manambolo River

(19°15'S, 44°30'E) and Soahany River (18°40'S, 44°30’E),

about 300 km west of the capital, Antananarivo. This area

lies within the Western Malagasy phytogeographical re-

gion (Humbert 1954), which is characterized by annual

rainfall from 1000-2000 mm, monthly mean tempera-

tures above 20°C, and elevations less than 800 m. Thewet season begins in October or November and lasts

through March. The dry season begins in May and lasts

through September or October. The climax vegetation is

tropical dry deciduous forest, but savanna grasslands,

maintained by burning, dominate the landscape (Gml-

laumet 1984). Most lakes in the region are floodplain

lakes whose surface area varies considerably between wet

and dry seasons (Kiener and Richard-Vindard 1972).

During the 1997 breeding season (May-December),Platform Transmitter Terminals (PTTIOO Series®; Micro-

wave Telemetry 2000, Inc., Columbia MD) with antennas

hxed at 45*^, were mounted with a backpack style harness

on two fledgling fish-eagles. One transmitter (PTT No3482) was mounted on a female that was rescued froman aggressive sibling, raised in captivity, and released at

fledging age (Watson et al. 1996, 1999). This bird was

released by hacking (a falconry term for the process of

release to the wild; Cade 2000) into unoccupied, suitable

habitat at Lake Mangily (18°30'S, 44°34'E). The second

PTT (No. 3480) was put on a male that fledged naturally

from a fish-eagle pair on Lake Ankerika (19°03'S,

44°27'E), about 65 km south of the first. PTTs were pro-

grammed for 8 hr on, 24 hr off for six cycles; 8 hr on,

96 hr off for 84 cycles; and 8 hr on, 240 hr off for the

remaining life of the transmitter, to gain more frequent

locations of movements made in the first year, followed

by less frequent locations for the remaining life of the

PTT, which we expected to be at least 4 yr.

Satellite telemetry uses the ARGOS Data Collection

and Location System (Meyburg et al. 1995). ARGOS as-

signs PTT locations a grade according to calculated pre-

cision. We used only locations graded as within 1000 mof actual position. ARGOS reports two locations, one be-

ing a spurious mirror of the true location. We deducedthe true location using either concurrent visual obser-

vations, likelihood of sequential locations, or known hab-

309

310 Short Communications VoL. 36, No. 4

itat at each location. Locations were plotted in chrono-

logical order on a topographical 1:100 000 map. The pro-

gram Ranges IV® (Kenward 1990) was used to calculate

distances moved and range areas based on minimumconvex polygons (MCP) around locations.

Results

PTT No. 3480 on the male operated for 282 d, from

1 Decemher 1997-8 September 1998, providing 70 us-

able locations. From these locations, the total MCP range

of the male was 1040 km^ (Fig. 1). Between the fledging

date on 13 October 1997 and 17 April 1998 (186 d), the

male moved in a relatively small area around its nest site.

During the wet season, from December-March, the male

visited small lakes and flooded lowlands to the south and

southeast of its nest site along the Manambolomaty River

and Lakes Kakobo and Antsohaly, covering an area of

156.4 km^. By 24 April 1998, the male had moved north-

northwest with one location near Lake Mangily (the fe-

male’s release site) on the way. For 76 d at the beginning

of the dry season, from 13 May 1998-28 July 1998, the

male was located in the vicinity of the Soahanina River

estuary, and associated ponds and mangroves, ranging

over an area of 540.5 km^. The maximum distance re-

corded from its nest was 51 km. By 5 August 1998 and

through 8 September 1998, when the last usable trans-

mission was received, the male was located again in the

vicinity of the nest where his parents were raising a nest-

ling.

The PTT on the female operated for 348 d, from 15

October 1997-28 September 1998, providing 40 usable

locations (Fig. 2). We received 21 usable locations from

15 October 1997-22 November 1997 when the PTTceased transmitting for unknown reasons. It then re-start-

ed 80 d later on 11 February 1998 and we received an-

other 19 usable locations through 28 September 1998.

About 95% of usable fixes were <5 km from the release

site. Direct observation conhrmed that the bird movedaround Lakes Mangily and Sarny until held observations

ended 13 March 1998 due to inaccessibility from flood-

ing. The maximum distance recorded from the release

site was 8.2 km and the mean distance was 2.6 km. Thefemale’s MCP range was 45 km^.

Discussion

Usable locations for the male were sufficient to deter-

mine several aspects of the bird’s movement. Locations

were usually received 10 or more days apart, which lim-

ited the amount of detail that could be gained from

them, Initial movements of the naturally fledged male

were distances of 5-18 km to sites that may be visible to

a soaring bird from its natal site. The male made one

large movement of short duration 51 km to the north-

west, where he remained for 76 d, making successive

short movements, until returning to his natal site. All ar-

eas visited were without territorial, breeding pairs. Themale did not visit prominent wetland areas within his

MCP range where human disturbance was high, such as

Lakes Bemamba and Antsohaly.

The released female’s range during the wet season, as

water flooded the surrounding lowland areas, included

Lakes Mangily and Sarny, other small lakes, and a portion

of the Miharana River. Compared to the male, the female

made only very short movements around the release site

While it is possible that the low number of usable loca-

tions influenced her measured range area, results were

spread throughout a similar period to those of the male

and observations by our field team confirmed her loca-

tions during much of the study period.

The differences in movement patterns of the male and

female are interesting. They may be related to sexual dif-

ferences in behavior, but there are a number of other

factors that could influence dispersal. For example, nat-

urally-raised and fledged compared with captive-raised

and released by hacking might affect their behavior. So-

cial interactions with neighboring conspecifics, the nat-

urally fledged male had at least 10 territorial pairs near-

by; whereas, the female had only one resident pair within

5 km, which could have caused a difference in dispersal

behavior. Also, distribution of food during the wet-season

floods might influence movements.

Habitats visited by both eagles were lakes, rivers, man-

groves, and lowlands temporarily flooded during the wet

season. We assume that movements of fledglings were

made in exploration of suitable foraging habitat because

there was no seasonal pattern to the movements, and

they were of short distance and duration relative to the

species’ capacity for flight.

Despite the potential of satellite telemetry to track

birds for up to 4 yr, because no signal was detected from

the PTTs after about 18 mo, we were unable to learn

more about the occurrence of extra birds at the nest be-

yond the observation that the male returned to its par-

ent’s territory about 10 mo after fledging and remained

there at least a month while the adults were caring for a

nestling. Since this study, direct observation of banded

birds, and molecular studies of their genetic relatedness,

have revealed far more information (Tingay 2000, Tingay

et al. 2002).

Tracking additional birds to increase sample size need-

ed to compare dispersal between naturally-fledged and

captive-reared and released juveniles, and document hab-

itat use during dispersal, has not been attempted. Thepractical difficulties and cost of captive rearing in Mad-

agascar, and the cost of satellite telemetry, precluded fur-

ther study. Few studies have been done on post-fledging

dispersal in raptors (e.g., Walls and Kenward 1994) or

comparison between captive-raised and naturally-fledged

birds (e.g., Amar et al. 2000) probably for similar reasons.

As satellite telemetry becomes more efficient and afford-

able, these areas of study may benefit.

Satellite telemetry provided us with a level of coverage

and continuity, especially for long-distance movements,

that we could not have achieved for the male using con-

December 2002 Short Communications 311

44° 30’

E

Figure 1 . Chronological movements and minimum convex polygon range of the male Madagascar Fish-Eagle fledged

from a nest on Lake Ankerika.


Figure 2. Minimum convex polygon range of the captive-reared female Madagascar Fish-Eagle released by hacking

at Lake Mangily.


ventional VHF radios and tracking from the ground. Wemay have achieved similar results by VHF-radio tracking

from an aircraft, but lack of landing fields and fuel in

the study area precluded this approach. The pro-

grammed on-off cycle of the transmitters provided fewer

useful locations than we expected. A longer (e.g., 12-24

hr) on-cycle might have generated more usable locations

m these birds that were more sedentary than migrating

raptors. For example, two migrating Bald Eagles {Hal-

iaeetus leucocephalus) with PTTs programmed for 8 hr on,

16 hr off, and 4 hr on, 44 hr off cycles generated 205

fixes in 136 d and 27 fixes in 119 d, respectively (Grubb

et al. 1994). A migrating Wahlberg’s Eagle {Aquila wahl-

bergi) with a PTT programmed for 8 hr on, 134 hr off

generated 104 locations in 234 d (Meyburg et al. 1995).

A 12-24 hr on-cycle would increase the chance of satel-

lites passing over an eagle in optimum position (such as

m flight) to receive the transmitter’s signal. Transmission

of usable locations ceased for unknown reasons well be-

fore their anticipated 4-yr lifespan. Unexplained periods

of no data received added to our uncertainty of the birds’

movements.

We believe satellite telemetry is valuable for tracking

the movement of large birds of prey; however, there are

several limitations. The accuracy of locations within the

PTT’s operational period varied from day to day. Theprecision of the location is known to be affected by sev-

eral satellite parameters and by the orientation, location,

and movement of the transmitter. PTTs are at present

larger and less streamlined than conventional VHF trans-

mitters, and require antennas that protrude at a 45° an-

gle rather than contour down the back and the tail of

the bird. Also, PTTs are .substantially more expensive,

though this cost may compare favorably with the cost of

data collection from VHF radios which require personnel

in the field and logistical support,

Resumen.—En 1997, colocamos radio transmisores a dos

polluelos de aguilas pescadoras de Madagascar (Haliaee-

tus vociferoides) para estudiar sus movimientos y uso de

habitat durante la dispersion post emplumamiento. El

macho partio naturalmente del nido de sus padres dur-

ante Octubre y nosotros liberamos la hembra criada en

cautiverio el 15 de Octubre. El rango del aguila machofue 1040 km^ entre el 1 de noviembre de 1997 y el 8 de

septiembre de 1998 (70 localizaciones) y se movio unadistancia maxima de 51 km desde su area natal, al norte

del rio Soahanina, El comenzo moviendose largas distan-

cias (>5 km) el 16 de Diciembre de 1997, permanecio

en la vecindad del estuario del rio Soahanina por 76 dias,

entonces retorno a la vecindad del nido (<5 km) el 5 de

Agosto de 1998. El rango de la Hembra fue 45 km^ entre

el 15 de Octubre de 1997 y el 28 de Septiembre de 1998

(40 localizaciones) y se movio una distancia maxima de

8.2 km desde el sitio de liberacion. Los rios, lagos, mang-

lares y zonas bajas temporalmente inundadas durante la

temporada humeda fueron visitados por ambas aguilas.

Sugerimos que los movimientos de los volantones se hi-

cieron para explorar habitats de forrajeo adecuados, ya

que no hay un patron estacional para los movimientos, y

fueron relativamente de corta distancia y duracion con

respecto a la capacidad de vuelo de la e.specie.


ACKNOWLTDCiMEN'rS

This study was conducted by The Peregrine Fund’s

Madagascar Project with funding provided, in part, by

Environment Now, the Liz Claiborne and Art OrtenbergFoundation, the John D, and Catherine T. MacArthurFoundation, the Walt Disney Company Foundation, the

Little Family Foundation and other important contribu-

tors. The project received in-kind support from the Na-tional Aeronautics and Space Administration, UnitedStates Fish and Wildlife Service, and other partners. Weespecially thank David H. Ellis, Jon W. Robinson, andPaul Howey for their cooperation and support during

this project, and the constructive reviews of this manu-script byJames Berkelman, Mark Puller, and Robert Leh-

man.

Literature Cited

Amar, a., B.E. Arroyo, and V. Bretagnotle. 2000. Post-

fledgling dependence and dispersal in hacked and

wild Montagu’s Warriers Circus pygargus. Ibis 142:21

—

28.

Cade, T.J. 2000. Progress in tran.slocation of diurnal rap-

tors. Pages 343—372 in R.D. Chancellor and B.-U. Mey-

burg [Eds.], Raptors at risk. Hancock House/WWGBP, Berlin, Germany.

Grubb T.G., W.W. Bowerman, and P.H. Howey. 1994

Tracking local and seasonal movements of wintering

Bald Eagles Haliaeetus leucocephalus from Arizona and

Michigan with satellite telemetry. Pages 347—358 in

B.-U. Meyburg and R.D. Chancellor [Eds.], Raptor

conservation today. The Pica Press/WWGBP, Berlin,

Germany.

Guiliaumet, J.-L. 1984. The vegetation: an extraordinary

diversity. Pages 27-54 in A. Jolly, P. Oberle, and RAlbignac [Eds.], Key environments: Madagascar. Per-

gamon Press, Oxford, U.K.

Humbert, H. 1954. Les territoires phytogeographiques

de Madagascar, leur cartographic. Pages 195-204 in

Les divisions ecologiques du monde. Centre Nation-

ale de la Recherche Scientifique, Paris, France.

Kenward, R.E. 1990. Ranges TV. Institute of Terrestrial

Ecology, Wareham, England.

Kiener, a. and G. Richard-Vindard. 1972. Fishes of the

continental waters of Madagascar. Pages 477-499 in

R. Battistini and G. Richard-Vindard [Eds.], Bioge-

ography and ecology of Madagascar, Dr. W. Junk B VPublishers, The Hague, Netherlands.

Meyburg, B.-U. and C. Meyburg. 1999. The study of rap-

tor migration in the old world using satellite teleme-

try. Pages 2992-3006 in N.J. Adams and R.H. Slotow


[Eds.], Proc. 22nd Int, Ornithol. Congr. BirdLife

South Africa, Johannesburg, South Africa.

Meyburg, B.-U., J.M. Mendelsohn, D.H. Ellis, D.G.

Smith, C. Meyburg, and A.C. Kemp. 1995. Year-round

movements of a Wahlberg’s Eagle Aquila wahlbergi

tracked by satellite. Ostrich 66:135-140,

Rabarisoa, R., R.T. Watson, R. Thorstrom, and J. Ber-

kelman. 1997. The status of the Madagascar Fish-Ea-

gle Haliaeetus vociferoides in 1995. Ostrich 68:8-12.

Rafanomezantsoa, S.A. 1997. Behavior and natal dis-

persal of fledgling Madagascar Fish-Eagles. Pages

403-412 in R.T. Watson [Ed.], Madagascar wetlands

conservation project. Progress report III, The Pere-

grine Fund, Boise, ID U.S.A.

. 1998. Contribution a 1’etude des comportements

et de la dispersion des jeunes pygargues de Madagas-

car Haliaeetus vociferoides (Desmurs 1845) dans le com-

plexe des 3 lacs d’Antsalova. Memoire de D.E.A. Univ-

ersite d’Antananarivo, Madagascar.

and L. Kalavaha. 1999. Transfert de jeunes Py-

gargues de Madagascar. Pages 115-123 in A. Andri-

anarimisa [Ed.]. Projet de conservation des zones

humides de Madagascar. Rapport d’avancement V,

1997-1998. The Peregrine Fund, Antananarivo, Mad-

agascar.

Statterseield, AJ. and D.R. Capper. 2000. Threatened

birds of the world. Lynx Edicions, Barcelona, Spain.

Tingay, R.E. 2000. Sex, lies, and dominance: paternity

and behaviour of extra-pair Madagascar Fish-Eagles.

M.S. thesis. University of Nottingham, U.K.

, M. CuLATR, E.M. Hallerman, R.T. Watson, and

J.D. Fraser. 2002. Subordinate males sire offspring in

Madagascar Fish-Eagle {Haliaeetus vociferoides) polyan-

drous breeding groups. /. Raptor Res. 36:280-286.

Wau.s, S.S. and R.E. Kenward. 1994. Movements of ra-

dio-tagged Common Buzzards Buteo buteo in their first

year. lUs 137:177-182.

Watson, R.T, S. Thomsett, D. O’Daniel, and R. Lewis.

1996. Breeding, growth, development, and manage-

ment of the Madagascar Fish-Eagle {Haliaeetus vocifer-

oides). J. Raptor. Res. 30:21-27.

, S. Razaeindramanana, R. Thorstrom, and S. Ra-

fanomezantsoa, 1999. Breeding biology, extra-pair

birds, productivity, siblicide and conservation of the


Received 9 July 2001; accepted 28 June 2002

J. Raptor Res. 36(4) :315-319


Prey of the Peregrine Falcon {Falco peregrinus cassini) in

Southern Argentina and Chile

David H. Ellis^

USGS Patuxent Wildlife Research Center, HC 1 Box 4420, Oracle, AZ 85623 U.S.A.

Beth Ann SaboWildlife Forensics Services, P.O. Box 142613, Irving, TX 75014-2613 U.S.A.

James K. Fackler590 Davidson Road, Bow, WA 98232 U.S.A.

Brian A. Millsap

Fish and Wildlife Conservation Commission, 620 S. Meridian Street, Tallahassee, FL 32399 U.S.A.

Keywords; Peregrine Falcon; Falco peregrinus; Argentina;

Chile, Pallid Falcon; prey.

The Peregrine Falcon {Falco peregrinus cassini) in Pata-

gonia attracted wide interest two decades ago (Anderson

and Ellis 1981, McNutt 1984) when there was a focus on

determining the taxonomic position of the Pallid Falcon

(also called Kleinschmidt’s falcon and Tierra del Fuego

falcon; formerly named Falco kreyenborgi)

.

In 1981, how-

ever, the pallid falcon was confirmed to be a pale color

morph of the peregrine (Ellis et al. 1981, Ellis and Peres

1983), and since that time, little work has been conduct-

ed on this color morph. Continent-wide research has

continued and has yielded a fair understanding of the

breeding distribution of the Peregrine Falcon in South

America (Anderson et al. 1988, McNutt et al. 1988, Rise-

brough et al. 1990). Also, two preliminary food habits

studies on the peregrine have been completed in Pata-

gonia (McNutt 1981, Peres and Peres 1985). Together

those papers provided a list of 23 species observed as

prey, and McNutt (1981) listed another eight species

seen pursued (but not captured) by peregrines.

The purpose of this paper is to assemble all that has

been published on peregrine food habits for Patagonia

and Tierra del Fuego and to add to that list from our

1980 and 1981 expeditions.

Methods

In November-December of 1980 and 1981, we traveled

by motor vehicle searching for eyries in Chubut, Santa

Cruz, and Rio Negro provinces of Argentina and in Ma-gallanes, Chile. Although we accessed 16 eyries, somewere empty (prey remains sometimes scatter in the

wind), so our totals included prey from only 11 eyries.

We accessed eyries (normally by rope) and recovered re-

cent prey (feathers, feet, and bones with tendons at-

^ E-mail address: [email protected] or dcellis®

theriver.com

tached) but discarded those bones that were so bleachedthat they may be attributed to former occupants of the

eyrie. Most of the prey were identified from whole feath-

ers. No pellets were used in this anaylsis. We included

some feathers from the base of the eyrie cliffs, but ex-

cluded those that were likely molted by other occupants

of the cliff. For example, several of our eyries were in old

Black-faced (formerly buff-necked) Ibis {Tkeristicus cau-

datus) nests within active ibis colonies. Although ibis

feathers were frequently found near these eyries andeven though we occasionally observed peregrines pursu-

ing ibis, we viewed these attacks near eyries as displace-

ment activities. Only once did we include an ibis as prey

and this was after finding four fresh feathers within an

eyrie which was neither beneath an ibis roost nor near

an ibis nest. McNutt (1981) observed peregrines killing

nestling ibis.

No food habits study based on prey remains is without

bias (Marti 1987, Bielefeldt et al. 1992). For peregrines,

bias derives from the fact that many prey individuals are

missed because prey are normally plucked before arrival

at the eyrie and many defleshed carcasses are removedby the adults and deposited elsewhere. Also, several cast-

ings sometimes represent a single prey item. Commonprey are normally under represented in peregrine prey

tallies, including our sample, because of the difficulty of

totaling individuals. Our method was to derive a mini-

mum count from feet, bills, remiges, and rectrices. Forexample, a sample of 300 feathers and assorted other

remains from one species, and probably representing

dozens of individuals, may yield a much smaller mini-

mum count. Conversely, rare prey are likely to be over

estimated in most studies including this one, because a

single feather, bill, or foot can document prey that wasaccrued only once.

Prey were placed in plastic bags and air dried by open-ing the bags in a windless situation on sunlit days andfumigated prior to identification at the U.S. National Mu-seum (USNM: Smithsonian Institute). At USNM, we as-

sembled a synoptic series including all known and mostof the likely prey species. Because USNM does not have

examples for all plumages of all Patagonian birds, wecould not determine species on nine individuals.

315


Table 1. Avian prey of the Peregrine Falcon in southern Patagonia and Tierra del Fuego.^’^ Numbers refer to

minimum number of items represented in remains. A plus ( + ) indicates that a taxa was documented, but the numberof Items was not reported. Nomenclature follows Sibley and Monroe (1990).

Family Scientific Name Common NameMcNutt198L^

Peres andPeres

19853

This

Study

3

Rheidae Rhea pennata Lesser Rhea + * 1*

Tmamidae Eudromia elegans Elegant Crested-Tinamou 2

Podicipedidae Podiceps major Great Grebe 1

Procellariidae Halobaena caerulea Blue Petrel +

Pachyptila belcheri Slender-billed Prion -t-

Pelecanoididae Pelecanoides magellani Magellanic Diving-Petrel -f

Pelecanoides sp. 3

Ardeidae Nycticorax nycticorax Black-crowned Night-Heron 1

Threskiornithidae Theristicus caudatus Buff-necked Ibis *7*4 1

Anatidae Chloephaga picta Upland Goose

Anas sp. 1

Anas flavirostris Speckled Teal 2 1

Anas platalea Red Shoveler 1

Falconidae Falco sparverius American Kestrel 2

Phasianidae Callus gallus domesticus Domestic Chicken 1*

Rallidae Fulica leucoptera White-winged Coot 1

Charadriidae Vanellus chilensis Southern Lapwing 1 -t- 3 & 2*

Charadrius falklandicus Two-banded Plover -f

Charadrius modestus Rufous-chested Plover -h

Oreopholus ruficollis Tawny-throated Dotterel 1 -f 7 & 1*

Scolopacidae Fimosa haemastica Hudsonian Godwit -f

Gallinago stricklandii Fuegian Snipe 1

Thmocoridae Thinocorus orbignyianus Gray-breasted Seedsnipe 2 -f 4

Thinocorus rumicovorus Least Seedsnipe 17 + 5

Laridae Sterna sp. 2

Sterna hirundinacea South American Tern +

Columbidae Zenaida auriculata Eared Dove 16

Metriopelia melanoptera Black-winged Ground-dove 1

Columba livia Rock Dove -f

Psittacidae Cyanoliseus patagonus Burrowing Parakeet 2

Enicognathus ferrugineus Austral Parakeet 4 1

Caprimulgidae Caprimulgus longirostris Band-winged Nightjar 1

Furnariidae Geositta cunicularia Common Miner 3

Upucerthia dumetaria Scale-throated Earthcreeper 2

Eremobius phoenicurus Band-tailed Earthcreeper 2

Cinclodes fuscus Bar-winged Cinclodes 1

Cinclodes patagonicus Dark-bellied Cinclodes 4

Feptasthenura aegithaloides Plain-mantled Tit-Spinetail 1

Tyrannidae Neoxolmis rufiventris Chocolate-vented Tyrant 1 + 2

Muscisaxicola macloviana Dark-faced Ground-Tyrant 1

Fessonia rufa Patagonian Negrito 1

Hirundinidae TachyrAneta nieyeni Chilean Swallow 2

Notiochelidon cyanoleuca Blue-and-white Swallow 2

Troglodytidae Troglodytes musculus Tropical House-Wren +

Sturnidae Mimus patagonicus Patagonian Mockingbird 1

Muscicapidae Turdus falcklandii Austral Thrush 2 -1- 2


Table 1. Continued.

Family Scientific Name Common NameMcNutt198U

Peres andPeres

19853

This

Study3

Montacillidae Anthus correndera Correndera Pipit 1

Fringillidae Agelaius thilius Yellow-winged Blackbird 1

Sturnella militaris Pampas Meadowlark +Sturnella loyca Long-tailed Meadowlark 1

Molothrus bonariensis Shiny Cowbird 1

Phyrgilus gayi Grey-hooded Sierra-Finch 1

Phyrgilus fruticeti Mourning Sierra-Finch 3

Phrygilus unicolor Plumbeous Sierra-Finch 1

Melanodera melanodera Canary-winged Finch 1

Diuca diuca Common Diuca-Finch 3

Sicalis luteola Grassland Yellow-Finch 3

Carduelis barbata Black-chinned Siskin 1

Unknown 8 0 9

Total individuals 53+ unknown 102

Total identified

individuals 45 unknown 93

Minimum no. species 13 17 42

^ Not listed is a Kelp Gull (Larus dominicanus) observed as prey of a juvenile Pallid Falcon on 10 March 1979 (Ellis and Glinski 1980)

^ Nonavian prey include only a lizard {Liolaemus sp.) and a small rodent.

^ An asterisk (*) in these columns identifies prey that had not achieved adult size.

It is not certain that all 7 ibis were nestlings when taken.

We identified feathers by placing materials from oneeyrie in a shallow white box and from prior experience

sorted the feathers into piles tentatively assigned to a like-

ly taxon. A representative feather was grasped by forceps

then compared to specimens of likely donor species.

Once a good match for size, color, and pattern was

found, the pile of feathers was sorted to remove any that

did not represent this species and morph. Then the pro-

cess was commenced anew. After one of us completed anidentification for feathers without unique color patterns

(and most passerine primaries do not have bold color

patterns), a second person evaluated the feathers andconfirmed or rejected the identification. The most diffi-

cult materials often required an evaluation extending anhour or more before a certain match was found. Occa-

sionally, a feather had to be washed and blow dried be-

fore comparisons could be made. All identified materials

were bagged separately and archived.

In comparing feathers, it was often necessary to fan

the wing or tail on the museum skin; to do so without

tearing the skin required holding the appendage in

alignment with the body while deflecting the tip of the

feather with forceps. To aid in this process, we preparedflat skins with tail and one wing fanned for about 50 spe-

cies while in Argentina. For some other species, we mere-

ly placed wings, tail, feet, beak, and feathers representing

all body areas in a plastic bag. All specimens were deliv-

ered to the Argentine Museum of Natural Sciences,

Buenos Aires, Argentina, where the most valuable wereretained. The remainder were released for export andshipped to the U.S.A.

Results

From this and the previous two studies (McNutt 1981,

Peres and Peres 1985), we have documented a fair variety

of the prey taken by the peregrine in Patagonia. McNutt

(1981) identified 13 prey species and two other genera.

Peres and Peres (1985) noted 17 species, of which 10

were new (i.e., not previously noted by McNutt [1981])

The list from our study (Table 1) includes 42 species of

which 32 were not previously recorded. In summary, at

least 55 prey species in 26 families are known to be taken

by peregrines in Patagonia. To this can be added the

Kelp Gull {Larus dominicanus) recorded as prey of a ju-

venile Pallid Falcon seen on 10 March 1979 (Ellis and

Glinski 1980).

Discussion

Our list does not represent the full range of prey taken

by the Peregrine Falcon in South America, because first

of all, our study included only the southern fifth of the

distribution of this race. Second, other prey species are

known to be taken by this falcon in the Falkland Islands

(Cawkell and Hamilton 1961) and in more northerly re-

gions of South America (Hilgert 1988). Third, the low

numbers of individuals taken for common and likely prey

species (e.g., only two Austral Thrushes [Turdus falcklan-

dii\ and one Patagonian Mockingbird {Mimus patagoni-

cus)

)

suggest that much more variety will come from con-

318 Short Communications VoT. 36, No. 4

tmued sampling. The relationship between diversity (i.e.,

the number of species detected) and sample size can be

characterized as beginning with a 1:1 relationship but

with the plot soon leveling off and finally approaching

an upper asymptote (the true maximum in the numberof species taken) only after several hundred prey are tal-

lied (Heck et al. 1975, Marti 1987). At present, the total

for all three studies is less than 200 individuals. Further,

the two most commonly taken species in Table 1 were

represented by only ca. 23 and 16 individuals; before the

upper asymptote is reached, we expect that the numberof individuals of the most commonly-taken prey will ex-

ceed 100.

The list of species taken (Table 1) suggests that the

peregrine is prone to capture some prey on the ground.

The gosling was observed being taken on a gravel bar.

Surely, the young rheas, perhaps the tinamou, and likely

some of the other young birds in Table 1 were taken on

the ground. In addition to the avian prey tallied, we also

recorded one lizard {Liolaemus sp.) and a small mammal(Rodentia ca. 40 g); both of these would likely have been

taken on the ground (or kleptoparasitized) . In South

America there is no competing large falcon that hunts

terrestrial prey (i.e., like the Prairie Falcon [A mexicanus]

m North America and the Saker Falcon [A cherrug] in

Europe and Asia) that may constrain the Peregrine Fal-

con to an aerial foraging niche, so it was to be expected

that the peregrine in Patagonia would take quarry on the

ground more frequently than do some other races.

It is obvious from the variety of oceanic species on the

Peres list (Peres and Peres 1985; Table 1) that their study

emphasized coastal areas. Their sample was also from an

area where the pallid morph is relatively common (C.

Peres pers. comm.). Their results, in comparison with

our list for inland eyries, where the pallid morph is rare,

suggest that pallid and dark peregrines hunt different

prey. To document this potential difference (i.e., to com-

pare the foraging niches of two sympatric color morphs)

will surely be an interesting ecological study. Pallid and

normal birds appear very different in the field. Pallid

birds are less conspicuous and gull-like when seen be-

neath gray, overcast skies. We propose that the pallid

morph may have evolved when conditions were right for

a population of pale peregrines to live in isolation from

the population of normal peregrines further north on

mainland South America.

Resumen.—^A partir de publicaciones previas, conocemos

menos de 100 item presa que representan poco menosde 25 especies de aves para el halcon peregrine de la

Patagonia {Falco peregrinus cassini). Este estudio, incluye

presas de 11 nidos, anade 93 presas identificadas repre-

sentando 42 especies de aves (32 no reportadas previa-

mente), un lagarto, y un mamifero pequeno. Aunque do-

cumentamos una considerable variedad de presas para el

halcon peregrine en esta region, la frecuencia con la cual

nuevas presas fueron encontradas en cada nido visitado,

sugiere que la diversidad de aves tomadas fue mucho masgrande que la que se describe aqui. Esta alta diversidad,

en parte, resulta de variedades palidas y de color normal

que ocupan nichos de forrajeo un tanto diferentes.


Acknowledgments

In 1980, the U.S. Air Force funded much of our travel

Our 1981 work was largely funded by the National Geo-graphic Society and an anonymous philanthropist. Wethank Peter Simpson, manager of Estancia Chacabuco,Rio Negro, Argentina, for logistical support. Phil Angleidentified the lizard. Jamie Jimenez, Clayton White, andDavid Whitacre reviewed and improved the manuscriptOur thanks to staff at the USNM for allowing space for

our synoptic series and patience during the extendedtime devoted to identifying prey.

Literature Cited

Anderson, C.M. and D.H. Ellis. 1981. Falco kreyenborgi—a current review. Raptor Res. 15:33-41.

, T.L. Maechtle, and W.G. Vasina. 1988. Thesouthern breeding limit of the Peregrine Falcon. Pag-

es 251-253 mT.J. Cade,J.H. Enderson, C.G. Thelan-

der, and C.M. White [Eds.], Peregrine Falcon popu-

lations: their management and recovery. ThePeregrine Fund, Boise, ID U.S.A.

Bielefeldt, J., R.N. Rosenfield, andJ.M. Papp. 1992. Un-

founded assumptions about diet of the Cooper’s

Hawk. Condor 94:427-436.

Cawkell, E.M. and J.E. Hamilton. 1961. The birds of

the Falkland Islands. Ibis 103:1-27.

Ellis, D.H. and R.L. Glinskj. 1980. Some unusual re-

cords for the Peregrine and Pallid Falcons in South

America. Condor 82:350-351.

and C. Peres. 1983. The Pallid Falcon Falco krey-

enborgi is a color phase of the Austral Peregrine Falcon

{Falco peregrinus cassini). Auk 100:269-271.

, C.M. Anderson, and T.B. Roundy. 1981. Falco

kreyenborgi: more pieces for the puzzle. Raptor Res. 15.

42-45.

Heck, K.L., Jr., G. van Belle, and D. Simberloff. 1975

Explicit calculation of the rarefaction diversity mea-

surement and the determination of sufficient sample

size. Ecology 56:1459-1461.

Hii.gert, N. 1988. Aspects of breeding and feeding be-

havior of Peregrine Falcons in Guayllabamba, Ecua-

dor. Pages 749-755 in T.J. Cade, J.H. Enderson, C.GThelander, and C.M. White [Eds.], Peregrine Falcon

populations; their management and recovery. ThePeregrine Fund, Boise, ID U.S.A.

Marti, C.D. 1987. Raptor food habits studies. Pages 67-

80 in B.A.Giron Pendleton, B.A. Millsap, K.W. Cline,

and D.M. Bird [Eds.], Raptor management tech-

niques manual. Natl. Wildl. Fed. Sci. Tech. Ser. No10 .

McNutt, J.W. 1981. Seleccion de presa y comportamien-

to de caza del Halcon Peregrino {Falco peregrinus) en


Magallanes y Tierra del Fuego. An. Inst. Patagonia 12:

221-228.

. 1984. A Peregrine Falcon polymorph: observa-

tions of the reproductive behavior of Falco kreyenborgi.

Condor 86:378—382.

, D.H. Ellis, C. Peres, T.B. Roundy, W.G. Vasina,

AND C.M. White. 1988. Distribution and status of the

Peregrine Falcon in South America. Pages 237-249 in

T.J. Cade, J.H. Enderson, C.G. Thelander, and C.M.

White [Eds.], Peregrine Ealcon populations: their

management and recovery. Peregrine Fund, Boise,

ID U.S.A.

Peres, M. and C. Peres. 1985. Peregrine project, Argen-

tina (activities 1982). Bull. WWGBP 2:109-110.

Risebrough, R.W., A.M. Springer, S.A. Temple, C.M.

White, J.L.B. Albuquerque, P.H. Bloom, R.W. Fyfe,

M.N. Kirven, B.A. Luscombe, D.G. Roseneau, M.

Sander, N.J. Schmitt, C.G. Thelander, W.G. Vasina,

AND W. Walker, II. 1990. Observaciones del halcon

peregrino, Falco peregrinus subspecies, en America del

Sur. Rev. Bras. Biol. 50:563-574.

Sibley, C.G. and B.L. Monroe, Jr. 1990. Distribution and

taxonomy of birds of the world. Yale Univ. Press, NewHaven, CT U.S.A.

Received 7 January 2001; accepted 10 July 2002

J Raptor Res. 36(4) :320-323


An Elevated Net Assembly to Capture Nesting Raptors

Eugene A. Jacobs^

Linwood Springs Research Station, 1601 Brown Deer Lane, Stevens Point, WI 54481 U.S.A.

Glenn A. Proudfoot^Caesar Kleberg Wildlife Research Institute, Mail Stop 218, Texas A&M University-Kingsville,

Kingsville, TX 78363-8202 U.S.A.

Key Words: capture techniques-, dho-gaza; drop net, elevated

net, mechanical owl", mist net.

The use of a Great Horned Owl {Bubo virginianus) to

induce mobbing behavior, in combination with a net sys-

tem, has become the technique of choice for capturing

many species of nesting raptors (Hamerstrom 1963,

Bloom 1987, Bloom et al. 1992, Steenhof et al. 1994, Ja-

cobs 1996, McCloskey and Dewey 1999). However, some

species, and some individuals trapped previously, may be

reluctant to stoop at the owl when conventional tech-

niques (i.e., placing owl and nets near ground level) are

followed (Rosenfield and Bielefeldt 1993). In testing a

mounted and live Great Horned Owl to induce mobbing

behavior in American Kestrels {Falco sparverius)

,

Card et

al. (1989) found that the closer an owl decoy was placed

to the nest the more aggressive the kestrels became. Adecoy (mounted or live) placed near the nest of “trap

shy” Cooper’s Hawks {Accipiter cooperii) was more effective

than conventional techniques, but this method required

climbing tree(s) and was found to be time consuming

(Rosenfield and Bielefeldt 1993). Here we describe an

elevated net assembly that, in combination with an owl

decoy, proved successful for trapping five species of rap-

tors.

MATERIAI.S AND METHODS

The system consisted of an aluminum telescoping pole,

a horizontal cross bar, two vertical upright poles, a dho-

gaza type net (Clark 1981), and a mechanical owl

(equipped with two radio controlled servos that provided

movement to the owl’s head and perch) as described by

Jacobs (1996; Fig. 1). The cross bar that supported the

net assembly was a 3-m section of conduit tubing 2.5 cmin diameter. We used a commercially available conduit-

bending tool to form 90° angles 25 cm from each end of

the tubing, resulting in a “U ’’-shaped cross bar. A section

of sheet metal (45 cm X 45 cm) was then bent aroundthe cross bar to form a triangular bracket that enveloped

the cross bar. Using sheet metal screws, this sheet metal

envelope was attached to a 25-cm section of aluminum

‘ E-mail address: [email protected]

2 Present address: Department of Wildlife and Fisheries

Sciences, Room 210, Nagle Hall, Texas A&M University,

College Station, TX 77843-2258 U.S.A.

tubing 3 cm diameter at the center of the cross bar to

form a “T” that resembled the goal posts of most Amer-ican football fields. The “T” formation provided a stable

base for the net assembly and the diameter of the base

of the “T” allowed for quick insertion of the cross bar

to a telescoping pole. Two 2.2-m sections of conduit tub-

ing 1,8 cm in diameter were inserted into the upturned

ends of the cross bar to form the uprights that supported

the net. We used four tethered leads about 12 cm in

length, four metal rings (shower curtain rings) about 5

cm in diameter, and either wooden clothespins or mag-nets to attach the four corners of the net to the tops andbottoms of uprights. When clothespins were used, the

free ends of the tethered leads were held by clothespins

taped to the top two ends of the uprights. When magnets

were used, a metal washer tied to the free end of the

tethered leads provided support for the top two corners

of the net. The bottom two leads were attached to the

bottom of the uprights and remained stationary. Twometal rings were placed on each side of the net, one in

the top corner and one at the half-way point. The rings

attached the net to the uprights allowing the net to re-

main open during set-up, The rings also allow the net to

drop freely to the cross bar when a bird made contact

Once contact is made with the net, the net slides downthe uprights and creates a pocket entrapping the bird.

We inserted a 10-cm section of tubing (vertical, 1.1 cmin diameter) into the bottom of the owl’s perch and at-

tached a corresponding 30-cm section of tubing (0.9 cmdiameter) to the “T.” This was positioned so that about

15 cm of the tubing extended above the center of the

cross bar to support the owl’s perch.

The 2-8 m telescoping pole allowed us to adjust the

height of the net assembly to suit the nest site. Three guy

lines attached to the base of the “T” bracket stabilized

the net assembly when the telescoping pole was extendedto a height greater than 3 m. We used a 1-m section of

1 .3 cm diameter conduit tubing, hammered flat at oneend and cut to form a point, as support stakes for the

telescoping pole and 0.5 m stakes (fashioned the sameway) for the guy lines. Total cost of materials was ca. $250(U.S.); telescoping pole ($180), net (.$20), cross bar

($10), uprights ($10), anchor stake for telescoping pole

($10), guy lines and support stakes (.$10), and miscella-

neous material ($10).

Because vegetation structure varied among nest sites,

we elevated the net assembly to the maximum length of

the support pole (8 m) or to the highest feasible level

where tree branches blocked a greater extension. Thenet assembly was placed within 50 m of the nest tree, in

320


Figure 1. Elevated dho-gaza net assembly used to trap small- and medium-sized raptors near their nests.

view of the nest and with a clear flight path around the

net. Great Horned Owl vocalizations and conspecific calls

were utilized to lure nesting raptors to the net system(Bloom et al. 1992). A concealed observer was positioned

nearby (<100 m) to operate the radio controls to the

mechanical owl and record the sex of the adults whenthey were detected in the nest area (<50 m of nest). Theobserver (s) was able to sex all American Kestrels andSharp-shinned Hawks (A. striatus) from plumage char-

acteristics or relative size compared to their mates (Clark

and Wheeler 1987). We reported trapping success by us-

ing the number of birds trapped, divided by the numberof birds “tested” (birds detected within 50 m of the nest)

multiplied by 100.

When trapping Ferruginous Pygmy-Owls {Glaucidium

brasilianum)

,

we modified this system by downsizing the

net assembly (cross bar and uprights) to 2 m X 1 m,replacing the dho-gaza with a shortened 2-shelf mist net,

and replacing the mechanical owl with a conspecific

mounted decoy. This modified setup was used as de-

scribed above (using lure to induce mobbing behaviorfrom nesting owls), or simply placed in front of the nest

cavity entrance to capture the adults as they entered the

cavity to feed nestlings. The elevated mist net was placedabout 1.5 m from the nest cavity’s entrance.


During the breeding seasons (1994-2001) this tech-

nique was “tested” on five species of small to mediumsized raptors. Overall, we successfully captured 73% (113

of 154) of the individuals “tested.” Our trapping success


Table 1. Comparison of capture rates of elevated net with a mechanical owl, normal net with a mechanical owl, and

normal net with a live owl as a trapping technique for raptors.

Elevated Net with

Mechanical Owl(This Study)

Ground-level with

Mechanical Owl(Jacobs 1996)

Ground-level

with Live Owl

Red-shouldered Hawk 65% (30 of 46) 54% (15 of 28) 75% (199 of 264)1

Sharp-shinned Hawk 81% (34 of 42) 77% (48 of 62) —American Kestrel 70% (21 of 30) — 71% (15 of 21)2

97% (115 of 118)1

Cooper’s Hawk 67% (2 of 3) 60% (3 of 5) 52% (32 of 62)1

Ferruginous Pygmy-Owl 79% (26 of 33) — —' Data from Bloom et al. 1992.

^ Data from Steenhof et al. 1994.

was generally similar or slightly lower than studies using

a ground-level net set (height ^2.5 m) and live owl

(Bloom et al. 1992, Steenhof et al. 1994) and slightly

better than Jacobs (1996) found when using a normal

net set and a mechanical owl (Table 1 )

.

Bloom (1987) occasionally found it was difficult or

time consuming to capture both sexes of Northern Gos-

hawks (A. gentilis). Females were usually caught within 15

min, but males were often not captured. He speculated

that the male is less aggressive toward the owl during the

post-fledging period or is away from the nest (hunting)

and is unaware of the owl’s presence. With Sharp-

shinned Hawks and American Kestrels, we found of the

birds that were present (assumed to have seen the owl),

females responded more aggressively toward the owl

mount than did males. Trapping success for female

Sharp-shinned Hawks and female American Kestrels were

91% (21 of 23) and 79% (11 of 14), respectively. Males

of both species occasionally showed a reluctance to

“stoop” at the owl, resulting in a trapping success of 68%(13 of 19) for male Sharp-shinned Hawks and 63% (10

of 16) for male American Kestrels. The escape rate (per-

centage of birds that hit the dho-gaza net, but were not

captured) was 1.8% (2 of 113).

Benefits of this technique include: (1) a high response

rate; (2) a low escape rate; (3) the ability to readily adjust

net height; (4) minimal space (especially when com-

pared to a 12-m mist net) is required for setup; (5) this

technique kept the net off the ground, and hence, re-

quired less preparation time to reset the net after a cap-

ture when compared to a ground-level dho-gaza net.

Albanese and Piaskowski (1999) and Stokes et al.

(2000) have described similar techniques that use elevat-

ed mist nets to study birds that spend the majority of

their time in woodland canopies. However, those studies

used conventional mist nets in a manner designed for

continuous use at one location. Our technique was de-

signed to capture specific birds near their nest sites with

a mobile apparatus that allows researchers to visit multi-

ple locations with a minimal amount of setup time (ca.

15 min).

Even though we conducted 113 captures without any

visible injury, there is the potential for serious injury to

species that “stoop” at higher speeds and are of greater

mass than the Red-shouldered Hawk. A net that com-

pletely releases from the uprights (Bloom 1987) as well

as other modifications may be necessary to accommodate

the force of a larger raptor hitting the net. Alternatively,

because the “cut-down” mist net was successful in cap-

turing Ferruginous Pygmy-Owls as they approached or

exited the entrance to their nest cavity, this technique

should be effective for trapping most small cavity-nesting

birds without modification.

Resumen.—Debido a su alta tasa de exito, el uso de una

red de niebla en combinacion con un senuelo de Bubo

virginianus, es una de las tecnicas populaces mas usadas

para capturar rapaces durante su anidacion. Sin embar-

go, el protocolo estandar para esta tecnica limita su efec-

tividad a aves que tiene la habilidad de volar cerca al nivel

del suelo (<3 m) para atropellar al senuelo. Con el fin

de proveer una tecnica alternativa que pueda mejorar la

tasa de captura en algunas situaciones, construimos yprobamos un ensamblaje de redes elevado consistente de

un poste telescopico de aluminio, una barra cruzada hor-

izontal, dos postes verticales rectos, una red de niebla, yun buho raecanico. Desde 1994-2001, el exito en la cap-

tura de cinco especies de rapaces de talla pequena a me-

diana fue 73% (113/154 intentos). Debido a su adapta-

bilidad, el alto exito de captura y el bajo costo, este

sistema puede ser una herramienta beneficiosa para la

investigadon de las aves.


Acknowledgments

We thank D. Haessly and R. Rosenfield for providing

information on the effectiveness of our system on Amer-ican Kestrels and Cooper’s Hawks, respectively. J. Runke


provided the drawing in Figure 1. J. Bielefeldt, P. Bloom,

J Marks, M. McMillian, and B. Woodbridge provided

helpful suggestions for improving this manuscript.

Literature Cited

Albanese, G. and V.D. Piaskowski. 1999. An inexpensive

elevated mist net apparatus. N. Am. Bird Bander 24:

129-134.

Bloom, P.H. 1987. Capturing and handling raptors. Pag-

es 99-123 in B.A. Millsap, K.W. Cline, B.G. Pendleton,

and D.A. Bird [Eds.],Raptor management techniques

manual. Natl. Wildl. Fed., Washington, DC U.S.A

, J.L. Henckel, E.H. Henckel, J.K. Schmutz, B.

Woodbridge, J.R. Bryan, R.L. Anderson, P.J. De-

TRicH, T.L. Maechtke, J.O. McKinley, M.D. McCrary,

K. Titus, and P.F. Schempf. 1992. The dho-gaza with

Great Horned Owl lure: an analysis of its effectiveness

in capturing raptors./. Raptor Res. 26:167—178.

Clark, W.S. 1981. A modified dho-gaza trap for use at a

raptor banding station. J. Wildl. Manage. 45:1043-

1044.

and B.K. Wheeler. 1987. A field guide to hawks

in North America. Houghton Mifflin Co., Boston, MAU.S.A.

Card, N.W., D.M. Bird, R. Densmore, and M. Hamel1989. Responses of breeding American Kestrels to live

and mounted Great Horned Owls. J. Raptor Res. 23

99-102.

Hamerstrom, F. 1963. The use of Great Horned Owls in

catching marsh hawks. Proc. XIII Int. Ornithol. Congr

13:866-869.

Jacobs, E.A. 1996. A mechanical owl as a trapping lure

for raptors. / Raptor Res. 30:31-32.

McCloskey, J.T. and S.R. Dewey. 1999. Improving the

success of a mounted Great Horned Owl lure for trap-

ping Northern Goshawks./. Raptor Res. 33:168-169

Roseneield, R.N. and j. Bielefeldt. 1993. Trapping tech-

niques for breeding Cooper’s Hawks; two modifica-

tions. /. Raptor Res. 27:171-172.

Steenhof, K., G.P. Carpenter, and J.C. Bednarz. 1994

Use of mist nets and a live Great Horned Owl to cap-

ture breeding American Kestrels. J. Raptor Res. 28.

194-196.

Stokes, A.E., B.B. Schultz, R.M. Degraaf, and C.R

Griffin. 2000. Setting mist nets from platforms in the

forest./. Field Ornithol. 71:57-65.


J Raptor Res. 36(4):324-327


Florida Bald Eagle (Haliaeetus leucocephalus) Egg Characteristics

M. Alan Jenkins, 1 Steve K. Sherrod, David A. Wiedenfeld, and Donald H. Wolfe, Jr.

George Miksch Sutton Avian Research Center, RO. Box 2007, Bartlesville, OK 74005 U.S.A.

Key Words: Bald Eagle, Haliaeetus leucocephalus; eggs\

eggshell characteristics', pesticides.

The Bald Eagle {Haliaeetus leucocephalus)

,

south of the

40th parallel, was declared endangered by the U.S. Fish

and Wildlife Service in 1967 owing to an observed pop-

ulation decline in the 48 contiguous states, which was

hrst noticed in Florida. A population of eagles in western

peninsular Florida showed a sharp decline by 1957-58

(Broley 1958), and in eastern-central Florida the species

declined by two-thirds between 1951-61 (Howell 1963).

Those declines were later attributed to poisoning or the

weakening effects on eggshells caused by chlorinated hy-

drocarbon pesticide residues, notably DDE (Nisbet

1989). Eggs with shells thinned by DDE broke before

hatching, destroying the egg and resulting in lowered

productivity. From 1984—91 biologists with the George

Miksch Sutton Avian Research Center collected entire

clutches of Bald Eagle eggs from Florida nests as part of

a project to restore nesting populations of this species to

the southeastern U.S. (Sherrod et al. 1989). The eggs

were incubated and hatchlings were reared in Oklahoma,

and the young were released by hacking in eight south-

eastern states. This paper describes the physical charac-

teristics of 395 Bald Eagle eggs and the analysis of pesti-

cide residues in 15 unhatched eggs collected during that

project. We report the results of testing for correlations

between egg characteristics, location of collection, year,

sex of the eagle hatched, and information on organo-

chlorine pesticides and eggshell thickness.


Eggs were collected from nine counties in north-cen-

tral Florida (Fig. 1). At collection, each egg was markedwith a unique number, measured for length and breadth

with a caliper to the nearest 0.01 mm, and weighed to

the nearest 0.1 g (balance) or 0.01 g (electronic scale).

After incubation, the shells of hatched eggs were air-

dned and their thickness measured. Unhatched eggs

were frozen for as long as a year, a method of preserva-

tion which does not change the level of pesticide con-

centrations even if thawing and microbial degradation

occur (Stickel et al. 1984). Unhatched eggs were opened,

the contents removed, the shells were air-dried, and the

shell thickness measured.

Thickness measurements were made on fragments of

shell from three evenly spaced places near the equator.

Fragments were clamped in a hemostat and viewed with

a binocular microscope at lOOX. One microscope eye-

1 E-mail address: [email protected]

piece was equipped with a micrometer calibrated with a

stage micrometer. Each shell sample was viewed with the

microscope on its edge, the number of calibrations span-

ning the fragment recorded, and the thickness calculated

using a constant conversion factor obtained from the cal-

ibration (Enderson et al. 1982). The three thickness mea-surements of each egg were averaged.

Shell membranes of hatched eggs usually shrank, be-

coming detached from the shell and so they could not

be measured as part of the shell’s thickness. Shell mem-branes from unhatched eggs sometimes remained at-

tached after drying and, where possible, shells were mea-sured with attached membranes, then the membranesremoved and shell thickness re-measured. This gave shell

thicknesses with and without membranes for 37 eggs.

This allowed us to correct for loss of shell thickness

caused when shell membranes become detached. De-

tachment of the shell membranes after drying slightly

reduces the measured total shell thickness because the

mammillary tips from the shell come away attached to

the outer shell membrane during detachment (Terepka

1963).

Calculated egg volumes presented here include the

shell volume, a method preferable to trying to determine

inside volume (Stickel et al. 1973). The calculated vol-

ume formula was determined to be within —8 to +7 per-

cent of measured volumes for this species (Stickel et al

1973). Shell thicknesses may decrease during embryo de-

velopment as the embryo uses calcium from the shell for

bone formation (Romanoff and Romanoff 1949). How-ever, most of the decrease apparently occurs in the mam-millae core (Bond et al. 1988) and does not contribute

significantly to shell thinning (Bunck et al. 1985). Cal-

culated egg volume (V) was estimated using the formula

V = 0.508LB^ (Stickel et al. 1973), where L = length of

egg (cm) and B = breadth of egg (cm) . Calculated fresh

egg mass (M) was estimated as M = 0.56227LB^. Thecoefficient of 0.56227 yielded the best estimate of hatch-

ing date, assuming a period from the beginning of in-

cubation to pip of 33.5 d.

Unhatched eggs were considered fertile if they showedany sign of embryonic development upon dissection

Hatch order within clutches was recorded based on pip-

ping date and time. Hatch order was assumed to be iden-

tical with laying order because female eagles lay eggs a

few days apart and begin incubation with the first eggs,

making hatching within a clutch asynchronous (Gerrard

and Bortolotti 1988). However, time of pipping was only

accurate within ca. 12 hr because eggs were checked

twice daily for pipping.

Sex of fledgling-age eagles was determined from mea-

surements of bill depth and toepad length following the

methods of Walborn (1991).

Egg length, breadth, volume, length/breadth ratio, cal-

culated fresh mass, and shell thickness were checked for

324


Key to Counties

A = Alachua O = Osceola

H = Highlands Po = Polk

La = Lake Pu = PutnamLe = Levy S - Seminole

M = Marion V = Volusia

Figure 1. Florida Bald Eagle study area and counties of egg collections.

correlations with year and the latitude of the Florida

county where collected to determine any latitude trend.

Analysis of variance was used to compare shell thickness,

volume, and hatch order by sex; volume and shell thick-

ness (for all and for both sexes) by hatch order; andvolume and shell thickness with fertility. Statistical tests

were made using Systat statistical package, version 7.0.

Organochlorine and polychlorinated biphenyl pesti-

cide residues of the contents of 15 unhatched eggs wereanalyzed by Hazleton Labs using Food and Drug Admin-istration (1973) methods. The reported residues are

based on calculated fresh egg masses.

Results

No significant correlations were found between egg

length, breadth, volume, length/breadth ratio, calculat-

ed fresh mass, and shell thickness and the year of collec-

tion or the latitude of the Florida county where collected

(Table 1). There was a significant increase of eggshell

thickness from 1984-91 (T - 0.073, df = 392, P < 0.05)

However, the increase was not signihcant if data for 1984

were excluded. The 1984 sample size {N = 18) is biased

by the inclusion of an unusually thin-shelled two-egg

clutch with very high pesticide residues. One of these two

eggs was found broken in the nest; the other failed to

develop. The eggshells we collected were 4.5% thinner

than the pre-1947 Florida sample {N = 211) measured

by Anderson and Hickey (1972).

Residue analysis results for 23 chlorinated hydrocar-

bons, percent moisture and percent lipids for 15 un-

Table 1 . Summary of Florida Bald Eagle egg characteristics.

Length(L)

(mm)

Breadth

(B)

(mm)

Calculated

Volume(mm^) L/B Ratio

Calcuiated

Fresh Mass

(g)

Shell

Thickness

WithoutMembranes

(mm)

N 392 392 392 392 392 395

Minimum 64.38 48.34 82.30 1.166 90.92 0.312

Maximum 79.50 59.88 140.20 1.517 154.92 0.553

Mean 71.04 55.37 111.08 1.284 122.71 0.453

Standard Deviation 2.732 1.690 9.233 0.051 10.20 0.035


Table 2. Summary of chlorinated hydrocarbon pesti-

cide residues in 15 unhatched Florida Bald Eagle eggs,

1984-91. Data are corrected to calculated fresh egg mass-

es

Mean(ppm)

Maxi-

mum(ppm)

Mini-

mum(ppm)

Stan-

dard

Devia-

tion

DDE 2.47 10.10 0.66 2.35

DDD 0.05 0.58 0.0 0.14

DDT 0.24 3.89 0.0 0.94

HCB ND*Alpha-BHC NDGamma-BHC (lindane) NDBeta-BHC NDHeptachlor NDAldrin NDOctachlorostyrene NDHeptachlor epoxide 0.01 0.07 0.00 0.02

Oxychlordane 0.06 0.26 0.00 0.06

Gamma-chlordane 0.04 0.15 0.00 0.04

Alpha-chlordane NDTransnonachlor 0.29 1.06 0.00 0.25

Mirex NDDieldrin 0.10 0.66 0.00 0.15

Endrin NDMethoxychlor NDToxaphene NDPCB 1260 5.13 15.47 0.00 5.50

PCB 1248 0.02 0.24 0.00 0.06

PCB 1254 5.82 28.15 0.00 8.03

Percent moisture 80.78 83.60 76.00 2.04

Percent lipids 5.15 12.00 2.20 2.19

ND = None detected above detection limit of 0.1 ppm or lower.

hatched eggs are presented in Table 2 as benchmark data

for possible future information on this population.

Discussion

Bald Eagle body size is known to increase with increas-

ing latitude (Stalmaster 1987), but we found no correla-

tion of egg size characteristics with the small latitude span

we sampled. We speculated that eggs laid later in a clutch

might be smaller than the first, but our data failed to

detect such a trend. Likewise, sex of the eagles hatched

did not correlate with size of the egg or hatch order.

We expected an increase in eggshell thicknesses and

lessening of chlorinated hydrocarbon residues during the

years of our study because most uses ofDDT in the U.S.A.

have been banned; however, our thickness data did not

show a change over time during the period of our study.

The residues for our eggs, except one egg with high DDEresidues, are below the threshold levels indicated by

some authors as sufficient to affect raptor productivity

(Fyfe et al. 1988, Nisbet 1989, Risebrough 1989). Meanproductivity of Florida Bald Eagles during the years of

egg collection was 1.10 young/occupied territory (Nes-

bitt et al. 1998), and above the minimum of 1.0 young/

occupied territory that Wiemeyer et al. (1993) consid-

ered as representing a healthy population. Based on

these data, we believe that by 1984 the population of nest-

ing Bald Eagles in the areas of Florida from which wecollected eggs were reproducing at a rate that met the

criteria suggested by Wiemeyer et al. (1993). This pop-

ulation was relatively free of pesticide contamination and

that eggshell thinning was no longer a problem.

Resumen.—Las medidas y calculos de las medidas de 395

huevos de aguilas calvas {Haliaeetus leucocephalus) colec-

tados en Florida desde 1985-91 fueron evaluadas por me-

dio de relacion estadistica para el ano de coleccion, la-

titud del condado donde fueron colectados, sexo del

polluelo y orden de salida del huevo. No se encontraron

correlaciones significantes. Se hicieron analisis de resi-

duos de pesticidas organoclorados y bifenil policlorina-

dos en 15 huevos sin empollar. Con excepcion de una

nidada, los residues organoclorados fueron bajos.


Acknowledgments

Cooperation for this project was given by the Florida

Game and Fresh Water Fish Commission, in particular

Don Woods and Steve Nesbitt; The University of Florida,

especially Michael Collopy, Petra Bohall Wood, and Rob-

ert Rosen; and the U.S. Fish and Wildlife Service’s En-

dangered Species Program and Regions 2 and 4. Grateful

thanks are due to our numerous funders and the Sutton

Board of Directors. Many Sutton employees worked tire-

lessly to make the restoration project successful, Alan Be-

ske, Gwyn McKee, and Sheryl Tatora in particular. JamesEnderson loaned eggshell measuring equipment. Themanuscript was greatly improved by comments fromStanley N. Wiemeyer, James C. Bednarz, Sally Jenkins,

and two anonymous reviewers.

Literature Cited

Anderson, D.W. and J.J. Hickey. 1972. Eggshell changes

in certain North American birds. Pages 514-540 in

K.H. Voous [Ed.], Proc. XV Int. Ornithol. Congr. Leiden,

Germany.

Bond, G.M., R.G. Board, and V.D. Scott. 1988. A com-

parative study of changes in the fine structure of avian

eggshells during incubation. Zool.J Linn. Soc. 92:105-

113.

Broley, C.L. 1958. The plight of the American Bald Ea-

gle. Audubon 60:162-163, 171.

Bunck, M.M., J.W. Spann, O.H. Patee, and W.J. Fleming

1985. Changes in eggshell thickness during incuba-

tion: implications of evaluating the impact of organ-

ochlorine contaminants on productivity. Bull. Environ

Contam. Toxicol. 35:173-182.

Enderson, J.H., G.R. Craig, W.A. Burnham, and D.D.

December 2002 Short Communications 32V

Berger. 1982. Eggshell thinning and organochlorine

residues in Rocky Mountain peregrines, Falco peregti-

nus, and their prey. Can. Field-Nat. 96:255-264.

Food and Drug Administration. 1973. Pesticide analyt-

ical manual. Vol. 1, Washington, DC U.S.A.

Fyfe, R.W., R.W. Risebrough, J.G. Monk, W.M. Jarman,

D.W. Anderson, L.F. Kief, J.L. Linger, I.C.T. Nisbet,

W. Walker, II, and BJ. Walton. 1988. DDE, produc-

tivity, and eggshell thickness relationships in the ge-

nus Falco. Pages 319—335 in T.J. Cade, J.H. Enderson,

C.G. Thelander, and C.M. White [Eds.], Peregrine

Falcon populations: their management and recovery.

The Peregrine Fund, Boise, ID U.S.A.

Gerrard, J.M, and G.R. Bortolotti. 1988. The Bald Ea-

gle. Smithsonian Institution, Washington, DC U.S.A.

Howell, J.C. 1963. The 1961 census of some Bald Eagle

nests in east-central Florida. Auk 79:716-718.

Nesbitt, S.A., M.A. Jenkins, S.K. Sherrod, D.A. Wood,A. Beske, J.H. White, P.A. Schulz, and S.T. Schwik-

ert. 1998. Recent status of Florida’s Bald Eagle pop-

ulation and its role in eagle reestablishment efforts in

the southeastern United States. Proc. Annu. Conf.

Southeast. A.ssoc. Fish Wildl. Agencies 52:377-383.

Nisbet, I.C.T. 1989. Organochlorines, reproductive im-

pairment, and declines in Bald Eagle (Haliaeetus leu-

cocephalus) populations: mechanisms and dose-re-

sponse relationships. Pages 483-489 in B.-U. Meyburg

and R.D. Chancellor [Eds.], Raptors in the modernworld. WWGBP, Berlin, Germany.

Risebrough, R.W. 1989. Toxic chemicals and birds of

prey: discussion at Eilat in 1987. Pages 515-525 in

B.-U. Meyburg and R.D. Chancellor [Eds.], Raptors

in the modern world. WWGBP, Berlin, Germany.

Romanoff, A.L. and AJ. Romanoff. 1949. The avian egg.

John Wiley and Sons, Inc., New York, NY U.S.A.

Sherrod, S.K., M.A. Jenkins, G. McKee, D.H. Wolfe, Jr ,

and S. Tatom. 1989. Restoring nesting Bald Eagle

Haliaeetus leucocephalus populations to the southeast-

ern United States. Pages 353-357 in B.-U. Meyburgand R.D. Chancellor [Eds.], Raptors in the modernworld. WWGBP, Berlin, Germany.

Stalmaster, M.V. 1987. The Bald Eagle. Universe Books,

New York, NY, U.S.A.

Stickel, L.F., S.N. Wiemeyer, and LJ. Blus. 1973. Pesti-

cide residues in eggs of wild birds: adjustment for loss

of moisture and lipid. Bull. Environ. Contam. Toxicol 9

193-196.

Stickel, W.H., L.F. Stickel, R.A. Dyrland, and D.H.

Hughes. 1984. Comparison of methods of preserving

tissues for pesticide analysis. Environ. Monit. Assess. 4-

113-118.

Terepka, A.R. 1963. Organic-inorganic interrelationships

in avian egg shell. Exp. Cell Res. 30:183-192.

Walborn, E.B. 1991. Use of morphometric measure-

ments in determining sex of southern Bald Eagles.

M.S. thesis, Oklahoma State University, Stillwater, OKU.S.A.

Wiemeyer, S.N., C.M. Bunck, and C.J. Stafford. 1993.

Environmental contaminants in Bald Eagle eggs

(1980-1984) and further interpretations of relation-

ships to productivity and shell thickness. Arch. Environ.

Contam. Toxicol. 24:213—227.

Received 7 January 2002; accepted 25 July 2002

J Raptor Res. 36(4):328-331


Osprey Ecology in the Mangroves of Southeastern Brazil

Robson Silva e Silva^

Rua Sdo Jose 48/31, 11040-200, Santos, SP, Brazil

Fabio OlmosLargo do Paissandu 100/4C, 01034-010, Sdo Paulo, SP, Brazil

Key Words: Osprey; Pandion haliaetus; Brazil; diet; man-

grove, wintering ecology.

The Osprey {Pandion haliaetus) is a widely distributed

raptor found in every continent but Antarctica. The Eur-

asian nominate and North American subspecies {P. h. car-

ohnensis) make extensive migrations, the latter being a

trans-equatorial migrant wintering in United States (Flor-

ida), Mexico, Central America and South America from

Colombia to Argentina and Chile (Poole 1989, del Hoyoet al. 1994, Martell et al. 2001).

In Brazil, Ospreys have been recorded in almost every

state and month, but most records were made between

September and April (Sick 1997). The Amazon basin,

where reports are most common, seems to be the main

wintering area for Ospreys in the country, but there are

also clusters of records in coastal localities (Sick 1997,

Olmos and Silva e Silva 2001). Band recoveries made in

Brazil show the birds come from the Mid-Atlantic and

northeastern USA (Poole and Agler 1987).

Despite being a well-known species in its breeding

grounds (del Hoyo et al. 1994), there is little information

on the wintering ecology of Ospreys in South America

(Saggese et al. 1996), although detailed studies have

been made in Africa (Prevost 1982, Boshoff and Palmer

1983). Ospreys spend most of the year (six or moremonths) in their wintering grounds, so information on

their ecology during this period is critical for a clearer

understanding of their life-histories and the pressures

laced by the birds outside the breeding season. Here, we

provide an account of the ecology of Ospreys using a

mangrove eco.system in southeastern Brazil, the first such

study in South America.

SruDY Area AND Methods

The study was conducted in the mangrove ecosystem

that covers the estuarine area between Sao Vicente Island

and the mainland, in the coast of Sao Paulo state, south-

eastern Brazil (ca. 23°53'S, 46°23'W). This area, belong-

ing to the Santos and Cubatao counties, is part of the

major mangrove ecosystem located in the region knownas Baixada Santista, covering 120 km^, and located in oneof the most populated and developed areas in Brazil

(Lamparelli 1999). The local climate is hot and humid,with annual rainfall ranging from 2000 to over 2500 mm.


Winter is the driest season, the lowest rainfall occurring

in July-August, the highest values occurring between Sep-

tember-March (Olmos and Silva e Silva 2001). For a gen-

eral description of the area’s geography and environ-

ment, see CETESB (1991) and Olmos and Silva e Silva

(2001 ).

The main feature in the study area is a channel (Pia-

gaguera channel) bisecting it and connecting Santos Bayto the estuarine area inland. This broad (ca. 1 km wide)

channel is mostly man-made and regularly dredged to

allow for the passage of cargo ships serving the local steel

and fertilizer plants. Because of dredging and silting,

there are large mudflats along the channel. Ten naviga-

tion buoys and six concrete towers dot the entire length

of the channel and are used as perches by feeding Os-

preys. Prey remains accumulate on top of these buoysand towers, making collecting the collection of dietary

data simple. Three rivers (Quilombo, Casqueiro, and Cu-

batao) empty into the channel.

Diet and behavioral data were collected as part of a

broader study of the mangrove avifauna conducted fromMarch 199T-July 2000 during 231 field-days (Olmos andSilva e Silva 2001). Data on Osprey abundance through-

out the year and habitat use were gathered between Au-gust 1995-November 1996, when we made 36 standard-

ized bird censuses by boat along a 19.25 km transect

covering all habitats present (Olmos and Silva e Silva

2001 ).

Habitat classification was adapted from the mappingmade by Sao Paulo state’s environmental agency (CE-

TESB 1991) and represents a gradient of mangrove tree

cover. Habitat categories sampled were: mangrove forest

with mostly touching canopies and complete cover, de-

graded mangrove with many gaps between trees makinga patchwork of clearings, mangrove degraded by pollu-

tion, groups of mangrove trees, and large areas of her-

baceous growth dotted by dwarfed mangroves, a mosaic

of mudflats (with scattered mangrove trees), and ex-

posed mudflats without any tree cover. For a detailed de-

scription of habitats see Olmos and Silva e Silva (2001)

Feeding Ospreys were observed opportunistically with

the help of spotting scopes and binoculars with the aimof identifying the captured prey. Prey remains accumu-lated on buoys and towers were recovered during regular

checks and identified to the lowest possible taxonomiclevel by comparison to reference material.

Results

Ospreys were first recorded along the Piagaguera chan-

nel in 1986 (Olmos 1989). Interestingly, the species was

not found there earlier in the 20th century (Luederwaldt

328


Figure L Monthly numbers of Ospreys censused in the Santos-Cubatao mangroves, southeastern Brazil, between

August 1995-November 1996.

1919). It is almost impossible to tell adult birds from

young ones under field conditions (Boshoff and Palmer

1983), but we never observed newly-fledged Ospreys,

with their characteristic speckled plumage.

Ospreys are recorded in Santos-Cubatao throughorxt

the year. Census data show a peak during the austral sum-

mer and a minimum of three birds during the winter

(Fig. 1). Most (47%) records made during the censuses

were along the Cascalho River, where channel margins

are dominated by mangroves degraded by pollution (Ol-

mos and Silva e Silva 2001).

Table 1. Prey items of wintering Ospreys in the man-

groves of Santos and Cubatao, Brazil. Unidentified fish

were excluded.

Species N Percent

Mullets

Mugil sp. 69 76.7

Rhomboid mojarra

Diapterus rhombeus 16 17.8

Snooks

Centropomus sp. 2 2.2

Common trahita

Hoplias malabaricus 1 1.1

Brazilian mojarra

Eugerres brasilianus 1 1.1

Brazil geophagus

Geophagus brasiliensis 1 1,9

Total 90 100

From year-round census data. Ospreys had higher lin-

ear densities along rivers bordered by mangrove forest (x

= 0.71 birds/km) and mangroves degraded by pollution

(0.70 birds/km) compared to mudflats (0.2 birds/km)

and degraded mangrove (0.01 birds/km, Fij440 = 14 09,

P < 0.0001). Densities in mangrove forest and mangrove

degraded by pollution were not different, as well as dif-

ferences in densities between mudflats and degraded

mangroves (Tukey HSD test, both P < 0.001).

Most fish seem to be captured alive, but in November

1996, we did record an Osprey taking a dead fish floating

on the surface. The most important prey were mullets

(Mugil spp.) (76.7%) and rhomboid mojarra {Diapterus

rhomheus) (17.8%; Table 1). Only two freshwater fish,

common trahita {Hoplias malabaricus) and Brazil geopha-

gus {Geophagus brasiliensis) were recorded. One mullet

{Mugil platanus) left whole on a tower was 41. .5 cm TLand weighed 590 g, while a Diapterus rhombeus found mthe same circumstances was 30 cm and 490 g. Based on

prey remains and observations, fish smaller than 20 cmTL seem to be rare in the diet of Ospreys in southeastern

Brazil.

We rarely observed Ospreys hovering or flying low over

the water before capturing a fish. Once, an Osprey

caught a dying fish on the surface while “hovering.” In

most instances, the birds would soar over the water and

plunge dive rapidly after locating a fish. It was commonfor the birds to abort several dives (up to nine in a row)

before actually touching the water.

Ten out of 14 plunge dives by different birds were suc-

cessful (71%), with nine fish carried away and one falling

back to the water. After taking a fish, the birds would fly


to one of the available towers, buoys, trees, or when the

prey was too heavy, even a mudflat. All hsh were eaten

head first, discarding opercula and gills. Mullet viscera

were also discarded. Usually only the tail would remain

but, sometimes, we would find the posterior half of a

large mullet. After feeding, the bird would fly dragging

its feet in the water for over TO m. Sometimes up to three

birds were seen fishing in the same small area. When one

was successful the others would chase it amid much call-

ing, trying to steal its fish.

A curious behavior was observed on 22 August 1997,

at the Pia^aguera channel. One Osprey, while holding a

tree branch, was seen flying and calling after another in-

dividual. The second bird would perch, also calling. Thefirst bird flew out of sight but came back quickly, always

calling, without the branch. Both birds then began to

soar, always calling, making several aborted dives. After

one Osprey finally captured an unidentified fish, it flew

away being followed by the other bird. An Osprey flying

while holding a tree branch was also seen on 18 July

2000; this bird was chasing a Crested Caracara (Polyborus

plancus),but we soon lost sight of them.

Contrary to the behavior reported in some wintering

areas (Boshoff and Palmer 1983), Ospreys were very vo-

cal in Santos-Cubatao throughout the year, especially

when two birds came close to each other. It was commonto see two Ospreys soaring together with Black Vultures

( Coragyps atratus) while calling. They would also call whenwe approached the perch of a feeding bird, which caused

It to fly with its prey.

Yellow-headed Caracaras {Milvago chimachima) benefit

from Ospreys by scavenging fish remains from the feed-

ing perches, sometimes waiting beside a feeding Osprey.

Crested Caracaras are more aggressive and actively try to

steal fish from the Ospreys; sometimes up to four cara-

caras may join in a chase after an Osprey carrying a fish,

but we never saw them being successful. Interestingly,

Great Egrets {Casmerodius alhus) would expel Ospreys

Irom their feeding perches, while Kelp Gulls {Larus dom-

imcanus), known to steal Ospreys’ food in South Al'rica

(Boshoff and Palmer 1983), ignore them in Brazil.

Ospreys did not seem to be actively persecuted by local

people and the many fishermen using the mangroves.

Nevertheless, on 26 December 1996, a female was found

with a wounded wing, perhaps the result of being shot.

This bird is now in the ornithological collection of the

Museu de Zoologia da Universidade de Sao Paulo

(MZUSP 74346).

Discussion

The lack of records of newly-fledged Ospreys with their

characteristic speckled plumage suggests only birds over

1 yr-old migrate to the study area. The year-round pres-

ence of Osprey in Brazil raises the possibility the birds

might breed in South America, but no evidence has been

found so far (Sick 1997). Nevertheless, nesting in a win-

tering area has been documented in South Africa (Dean

and Tarboton 1983). The presence of Ospreys in Brazil

during April-August show non-breeders, juveniles, stay in

their wintering range.

Although Sick (1997) attested, without details, that Os-

preys sometimes take mammals and birds when winter-

ing, the only documented food items of Ospreys in Brazil

were fish, making the diet seem less diverse compared to

breeding areas (Wiley and Lohrer 1973). Mullets are de-

tritus-eating fish abundant in Brazilian estuaries, where

they gather in shoals year-round (Menezes 1983). Their

abundance, size, and the habit of sunning close to the

surface make them ideal prey for a plunge diver like the

Osprey. In fact, the only former report of a prey taken

by an Osprey in Brazil refers to a mullet (Mugil incilis)

(Martuscelli 1992), also taken in a mangrove area in

southern Sao Paulo state. Mullet was also the main prey

taken by wintering Ospreys in mangroves and estuaries

in Senegal (Prevost 1982) and South Africa (Boshoff and

Palmer 1983). The availability of mullet may probably ex-

plain why Ospreys seem to be the most common in coast-

al areas, especially estuaries and mangroves (Haver-

schmidt and Mees 1994). Fish were also the only prey

recorded as taken by Ospreys in freshwater habitats in

Peru (Willard 1985) and Argentina (Saggese et al. 1996),

the detritus-eating Prochilodus sp. being reported by both

studies. We observed a high capture success (71%) for a

limited number of foraging attempts on fish, but not out-

side the 40-70% range reported by studies elsewhere

(Poole 1989, del Hoyo et al. 1994).

There is no direct or intensive persecution of Ospreys

in southeast Brazil. Nevertheless, their reliance on detri-

tus-eating fish might be problematical. The Santos-Cu-

batao estuary receives the discharges of one of the major

industrial areas in Brazil, well-known in the 1980s for its

high pollution levels (Gutberlet 1996). Despite improve-

ments, the sediments still hold high levels of heavy metals

and organochlorines such as Hexachlorobenzene (HCB)

and Polycyclic aromatic hydrocarbons (PAHs). For ex-

ample, sediments from the Piagaguera channel hold

109.200 to 733.700 [xg/kg of benzopyrene, some of the

largest concentrations in the world (CETESB 2001).

These contaminants may be ingested by fish like mullet,

feeding on detritus and benthic algae, and accumulated

and transferred to piscivores like Ospreys. Thankfully,

most contaminants seem to be trapped in the sediment

and mullet samples generally have small concentrations

(CETESB 2001), although this situation may change if

dredging makes the compounds available again in the

water column.

RF..SUMEN.—Las aguilas pescadoras {Pandion haliaetus) son

registradas todo el ano en los manglares de Santos-Cu-

batao al suroriente del Brasil, con un pico de abundancia

entre diciembre y marzo. Las aves usan todos los habitat

del manglar pero las densidades lineares mas altas ocur-

ren a lo largo de rios bordeados por bosques de manglar

{x = 0.71 aves/km) y manglares degradados por polu-


cion (x = 0.70 aves/km). Las ûilas pescadoras fueron

registradas comiendo unicanaente pescado y mostraron

una alta tasa de exito (71% de los intentos). Los salmo-

netes {Mugil spp.) fueron el item de comida mas comun(77%), seguido por las mojarras romboides {Diapterus

rhombeus) (18%). A pesar de la historia de alta polucion

industrial del area, los niveles de contaminantes en las

especies presa consumidos por el aguila pescadora fu-

eron bajos, y la especie no fue perseguida por los pob-

ladores locales.


ACKNOWr.EDGMENTS

This work was possible through grants received fromFundaâo O Boticario de Protegao a Natureza, MacAr-thur Foundation and Ultrafertil S.A. to both authors. Weare very grateful for their timely support over the years.

We also thank Maria do Carmo Amaral (Cubatao Zoo,

Cotia-Para Ecological Park) for saving the Osprey speci-

men now in the MZUSP. Joel Escobar and the personnel

at Nautica da Ilha provided invaluable support when weneeded to deal with boats and outboard motors. We wish

to thank Mark Martell, Alan E. Poole, and Richard O.

Bierregaard, Jr. for comments and suggestions on im-

proving the manuscript.

Lu erature Cited

Boshoff, A.E. and N.G. Palmer. 1983. Aspects of the bi-

ology and ecology of the osprey in the Cape Province,

South Africa. Ostrich 54:189-204.

Companhia Estadual de Tecnologia e Saneamento Am-

biental. 1991. Avaliayao do estado de degradagao dos

ecossistemas da Baixada Santista. Sao Paulo, Brazil.

. 2001. Levantamento da contaminagao ambiental

do sistema estuarino Santos/Sao Vicente. CETESB,

Sao Paulo, Brazil.

Dean, W.R.J. and W.R. Tarboton. 1983. Ospreys breed-

ing records in South Africa. Ostrich 54:238-239.

Gutberlet,J. 1996. Cubatao: desenvolvimento, exclusao

social, degradaâo ambiental. Edusp/Fapesp, Sao

Paulo, Brazil.

del FIoyo, J., a. Elliott, and J. Sargatal (Eds.). 1994.

Handbook of the birds of the world. Vol. 2. New world

vultures to guineafowl. Lynx Edicions, Barcelona,

Spain.

Haverschmidt, E. and G.F. Mees. 1994. Birds of Surina-

me. Vaco Press, Paramaribo, Suriname.

IuAMPARELLI, C.C. 1999. Mapeamento dos ecossistemas

costeiros do estado de Sao Paulo. Secretaria do MeioAmbiente/CETESB, Sao Paulo, Brazil.

Luederwaldt, H. 1919. Os manguesaes de Santos. Rev

Mus. Paulista 11:310-409.

Martell, M.S., C.H. Henny, RE. Nye, and M.J. Soi.ensky

2001. Fall migration routes, timing, and wintering

sites of North American Ospreys as determined by sat-

ellite telemetry. Condor 103:715-724.

Martuscelli, P. 1992. Notas sobre aves pouco conheci-

das do estado de Sao Paulo. Pages 82-83 in Anais do

VI Encontro Nacional de Anilhadores de Aves, EDU-CAT, Pelotas, Brazil.

Menezes, N.A. 1983. Guia pratico para conhecimento e

identificayao das tainhas e paratis (Pisces, Mugilidae)

do litoral Brasileiro. Rev. Brasil. Zool. 2:1-12.

Olmos, E. 1989. A avifauna da baixada do polo industrial

de Cubatao. Rev. Bras. Biol. 49:373-379.

and R. Silva e Silva. 2001. The avifauna of a

southeastern Brazilian mangrove swamp. Int. J. Orm-

thol. 4:137-207.

Poole, A.F. 1989. Ospreys: a natural and unnatural his-

tory. Cambridge Univ. Press, Cambridge, U.K.

AND B. Agler. 1987. Recoveries of Ospreys band-

ed in the United States, 1914-84. y. Wildl. Manage. 51.

148-155.

Prevost, Y.A. 1982. The wintering ecology of Ospreys in

Senegambia. Ph.D. dissertation, University of Edin-

burgh, Scotland.

Saggese, M.D., E.R. De Lucca, S.F. Krapovickas, andE.H. Haene. 1996. Presencia del aguila pescadora

{Pandion haliaetus) en Argentina y Uruguay. Hornero

14:44-49.

Sick, H. 1997. Ornitologia Brasileira. Editora Nova Eron-

teira, Rio de Janeiro, Brazil.

Wiley, J.W. and F.E. Lohrer. 1973. Additional records of

non-fish prey taken by Ospreys. Wilson Bull. 85:468-

470.

WiLlARD, D.E. 1985. Comparative feeding ecology of

twenty-two tropical piscivores. Ornithol. Monogr. 36.

788-797.

Received 8 February 2002; accepted 3 July 2002

/ RapiorRes. 36(4) :332-334

© 2002 The Raptor Research Foundation, Tnc.

Diet of Breeding Tropical Screech-Owls (Otus choliba) in Southeastern Brazil

Jose Carlos MottaJunior'Departamento de Ecologia, Instituto de Biociencias da Universidade de Sdo Paulo, 05508-900, Sdo Paulo, SP, Brazil

Key Words: Tropical Screech-Owl; Otus choliba; breeding

dieL; prey biomass; Brazil.

The Tropical Screech-Owl {Otus choliba) occurs east of

the Andes Mountains from Costa Rica to Uruguay and

northern Argentina, and is also found throughout muchol Brazil (Meyer de Schauensee 1966, Burton 1992, Sick

1993). It is one of the most common and widespread

neotropical owl species inhabiting forest edges, open

woodlands, savannas, and other habitats with some ar-

boreal cover, including urban areas (Sick 1993, del Hoyoet al. 1999). Despite its commonness and widespread dis-

tribution, little ecological information is available on this

species, except for some data concerning natural history

and breeding (Thomas 1977, Smith 1983). Food habits

have been described only qualitatively (e.g., Thomas

1977, Smith 1983, Gallardo and Gallardo 1984). Here, I

provide more detailed information about the diets of

nestling and adult Tropical Screech-Owls during the

breeding season. Data on nest locations and the timing

of reproduction in southeastern Brazil are also present-

ed


The study was conducted at Chacara Mattos/Faber-Cas-

tell (21°59'S, 47°56'W), located 1 km west of the city of

Sao Carlos, Sao Paulo State, Brazil. The 90 ha study area

consists primarily of Pinus spp. plantations with some sec-

ondary-grassland savanna. A small patch (3 ha) of dis-

turbed gallery forest also occurs in this area. The land-

scape surrounding the study area is sugar cane

plantations and the outskirts of the city of Sao Carlos,

fhe climate is a transition between Koppens’s Cwai andAwi, or rainy tropical with a wet (October-March) and a

dry (April-September) season (Tolentino 1967).

Four samples of pellet debris (representing ca. 30 pel-

lets) and six complete pellets were collected from three

occupied nest cavities. This material was washed through

a line mesh screen (0.2 mm) and oven-dried (5(LC) for

24 hr for storage arid analysis. Prey remains were identi-

hed by comparison with a reference collection madefrom material from the study. I also measured the mass

ol prey items collected from the study area. Individuals

m the prey remains were counted by pairing mandibles,

with the exception of beetles and ants, which were count-

ed by the number of heads, and scorpions by the numberof stings. The analyzed prey remains presumably were

from owlets and possibly adults. I also assumed that ver-

tebrate prey were entirely ingested like invertebrates, be-

cause crania and other body bones were always present

' E-mail address: [email protected]

in the pellets. Both prey remains and the reference col-

lection were deposited at the Departamento de Ecologia,

Universidade de Sao Paulo, Brazil.


All three nests were in cavities located at a height of

1.0-1. 5 m in dead Eucalyptus sp. tree trunks, presumably

made by woodpeckers originally. Smith (1983) pointed

out that Tropical Screech-Owl nests are typically located

in tree cavities. In spite of the monthly field excursions

to the study area during 1992-93, nests were only found

on 25 November 1992 (Nest 1 ,with one female and three

owlets), 28 October 1993 (Nest 2, with one female and

two owlets), and 6 November 1993 (Nest 3, with one fe-

male and three owlets). The three adult females inside

cavities were captured by hand and weighed with a spring

scale. The mean and standard deviation of body mass was

128.3 ± 11.7 g. Subsequently, the adults were placed back

into the cavities. Prey remains were collected the first

time the nest was found and shortly after owlets fledged.

Analysis of pellets and pellet debris revealed at least 34

species of prey consumed. Invertebrates, mostly orthop-

terans such as Lutosa brasiliensis, were most frequent in

the diet (Table 1). Spiders (Lycosidea) and ants (For-

micidea) were also important numerically. In terms of

biomass, invertebrates also prevail, however, the few ver-

tebrates found, represented a third of the consumed bio-

mass (Table 1).

The mean body mass of prey consumed by Tropical

Screech-Owls was 0.93 ± 2.35 g, ranging from 0.02-28.80

g {N = 309 prey items). Most prey (73.5%) weighed be-

tween 0. 1-1.0 g.

Tropical Screech-Owls only were observed foraging at

night. On two occasions, an individual was observed leav-

ing a perch on a tree and, in flight, capturing insects on

the leaves of another tree. On another occasion, an in-

dividual left a perch on a bush and captured an uniden-

tified invertebrate on the ground. Gallardo and Gallardo

(1984) reported a similar behavior in Tropical Screech-

Owls. 1 have observed these screech-owls catching insects

in flight, particularly in the vicinity of artificial light

sources, which was also reported by Smith (1983) and

Sick (1993). During the period of activity (1800-0600 H)

owls were observed on perches waiting for potential prey;

therefore, this species probably should be classified as a

“sit-and-wait” forager, which is typical for the genus Otus

(Jaksic and Carothers 1985).

The qualitative studies of Thomas (1977) and Smith

(1983) indicated that the diet of Tropical Screech-Owls

consisted mostly of insects in Costa Rica and both insects

332


Table 1. Prey items found in pellets and pellet debris of Tropical Screech-Owls in southeastern Brazil, with their

percentages in relation to total number and estimated biomass (g). Activity periods and sites of prey were determined

based on field observations and information provided by Manoel M. Dias (pers. comm.).

Prey Items Aciivn Y Period Activity Site

Pfrcfne

NumberPFRt:FNT

Biomass

Rodents

Bolomys lasiurus Nocturnal/crepuscular,

Diurnal

Ground 0.3 10.1

Calomys tener Nocturnal/crepuscular Ground 0.3 3.6

Oligoryzomys nigripes Nocturnal/crepuscular Foliage/branches,

Ground0.3 6.0

Opossums

Gracilinanus sp. Nocturnal/crepuscular Foliage/branches,

Ground0.3 5.7

Snakes

Unidentified small sp. p ? 0.3 3.3

Amphibians

Hylidae (unidentified sp.) Nocturnal/crepuscular Foliage/branches 0.3 5.3

SUBTOTAL VERTEBRATES — — 1.9 34.1

Scorpions

Bothriurus spp. Nocturnal/crepuscular Ground 3.6 1.0

Tityius bahiensis Nocturnal/crepuscnlar Ground 0.3 0.1

Spiders

Lycosidae (unidentified sp.) Nocturnal/crepuscular Ground 11.3 5.9

Unidentified spp. p ? 1.3 0.8

Harvestmen

Opiliones (unidentified sp.) p p 0.3 0.1

Insects

Blattidae {Parahormetica sp.) Nocturnal/crepuscular Ground 1.6 3.2

Blattidae (unidentified sp.) ? ? 0.3 0.2

Termitidae (workers) Nocturnal/crepuscular,

Diurnal

Ground 2.6 0.2

Acrididae spp. Diurnal Foliage/branches 2.9 1.4

Tettigoniidae (Copiphorinae) Nocturnal/crepuscular Foliage/branche s 5.8 6.0

Tettigoniidae (Conocephalinae) Nocturnal/crepuscular Foliage/branches 0.6 0.2

Gryllacrididae {Lutosa brasiliensis) Nocturnal/crepuscular Ground 41.1 34.2

Gryllidae Nocturnal/crepuscular Ground 1.6 1.6

Unidentified Orthoptera ? ? 0.6 0.3

Mantidae Nocturnal/crepuscular Foliage/branches 4.2 2.8

Carabidae (small unidentified spp.) Nocturnal/crepuscular Ground 1.0 0.1

Scarabaeidae (Rutelinae) Nocturnal/crepuscular Foliage/branches 0.3 0.3

Scarabaeidae (Dynastinae) Nocturnal/crepuscular Ground 2.6 3.1

Cerambycidae Nocturnal/crepuscular Tree trunks 1.6 2.4

Unidentified adult Coleoptera ? p 1.0 0 4

Unidentified larvae Coleoptera p ? 1.0 0.4

Lepidoptera (unidentified small moth) ? p 0.3 0 1

Lepidoptera (unidentified caterpillar) ? Foliage/branches 1.0 0 3

Formicidae {Atta sexdens queen) Nocturnal/crepuscular,

Diurnal

Ground 0.3 0.2

Formicidae {Camponotus Nocturnal/crepuscular,

Diurnal

Tree trunks,

Ground5.2 0.1

Formicidae (Dorylinae) Nocturnal/crepuscular,

Diurnal

Ground 1.9 0 1

Formicidae (unidentified spp.) ? p 3.2 0 1

Other unidentified Insecta ? ? 0.3 02

SUBTOTAF INVERTEBRATES — — 98.1 65 9


and vertebrates in Venezuela, respectively. Prey taken by

these owls include katydids, beetles, cockroaches, small

snakes, and rodents (Thomas 1977, Smith 1983, this

study). Larger species like Otus asio and O. kennicottii

seem to include proportionally more vertebrates in their

diets (e.g., Ritchison and Cavanagh 1992, del Hoyo et al.

1999). On the other hand, smaller species such as O.

tnchopsis, O. flammeolus, and O. choliba appear to be mostly

insectivorous (Ross 1969, del Hoyo et al. 1999, this

study)

.

The frequent consumption of the terrestrial arthro-

pods, Lutosa brasiliensis (Lycosidae) and others (68.5% by

number and 63.3% by biomass) suggests that prey are

often captured on the ground (Table 1). A similar pat-

tern in the prey data supports that the Tropical Screech-

Owls were essentially nocturnal; the diet consists mainly

of night prey (76.8% by number and 81.5% by biomass;

Table 1).

Resumen.—Se estudio la dieta del Autillo Choliba {Otus

choliba) durante el periodo reproductivo, entre los meses

de octubre y diciembre de 1992 y 1993, en nna localidad

del Sudeste de Brasil. Se identificaron por lo menos 34

especies de presas a partir de egagropilas, directamente

colectadas en tres nidos ubicados en cavidades de troncos

muertos a 1.0-1.5 m del suelo. Insectos, en especial Lu-

tosa brasiliensis (Gryllacrididae) y otros ortopteros, arahas

y escorpiones forraaron la base de la dieta. Aunque los

mvertebrados fueron los mas importantes numerica-

mente (98.1% del total de 309 individuos), los vertebra-

dos tuvieron representacion significativa en terminos de

biomasa consumida estimada (34.1% del total de 286.0

g) La inayoria de las presas eran nocturnas y terricolas,

mdicando los habitos de caza de esta lechuza.

[Traduccion del autor]

Acknowledgments

1 thank A.W. Faber-Castell S/A for facilities in the study

site. The entomologists Manoel M. Dias and Alejo M. Lar-

rambebere helped with invertebrate identihcation. Mar-

tha Desmond, F.R. Gehlbach, Gary Ritchison, and Clint

W Boal made valuable comments. Diego Queirolo kindly

revised the Spanish text. This work was a small part of a

Ph.D. dissertation sponsored by Coordenacao De Aper-

feigoamento Ce Pessoal De Nivel Superior and WorldWildlife Fund/Brazil.

Literature Cited

Burton, J.A. (Ed.). 1992. Owls of the world: their evo-

lution, structure, and ecology, 3rd Ed. Peter Lowe,

Wallingford, U.K.

DEL Hoyo, J., A. Elliott, and J. Sargatai.. 1999. Hand-

book of the birds of the world. Barn Owls to hum-mingbirds. Vol. 5. Lynx Edicions, Barcelona, Spain,

Gai.iardo, L.A. AND J.M. Gallardo. 1984. Observaciones

realizadas sobre el comportamiento de Otus choliba en

liberdad. Comun. Mus. Argent. Cienc. Nat. Bernardino

Rivadavia Zool. 4:109-114.

JAKSIC, F.M. AND J.H. Carothers. 1985. Ecological, mor-

phological, and bioenergetic correlates of hunting

mode in hawks and owls. Ornis Scand. 16:165-172.

Meyer de Schauensee, R. 1966. The species of birds of

South America and their distribution. Livingston, Nar-

berth, PA U.S.A.

Ritchison, G. and P.M. Cavanagh. 1992. Prey use by

Eastern Screech-Owls: seasonal variation in central

Kentucky and a review of previous studies. J. Raptor

Res. 26:66-73.

Ross, A. 1969. Ecological aspects of the food habits of

insectivorous screech-owls. Proc. West. Found. Vertebr.

Zool 1:301-344.

Sick, H. 1993. Birds in Brazil. A natural history. Princeton

Univ. Press, Princeton, NJ U.S.A.

Smith, S.M. 1983. Otus choliba. Pages 592-593 in D.HJanzen [Ed.], Costa Rican natural history, Univ. of

Chicago Press, Chicago, IL U.S.A.

Thomas, B.T 1977. Tropical Screech-Owl nest defense

and nestling growth rate. Wilson Bull 89:609-612.

Tolentino, M. 1967. Estudo critico sobre o clima da re-

giao de Sao Carlos. Concurso de Monograhas Muni-

cipals, Sao Carlos, Brazil.

Received 17 September 2001; accepted 5 July 2002

Associate Editor: Clint W. Boal

Letters

J. Raptor Res. 36(4):335-336


Comments on the First Nesting Record of the Nest of a Slaty-backed Forest-Falcon{Micrastur mirandollei) in the Ecuadorian Amazon

De Vries and Melo (2000,/. Raptor Res. 34:148-150) recently reported the first documented nest of a Slaty-backed

Forest-Falcon {Micrastur mirandollei), based on their studies in Yasuni National Park, Ecuadorian Amazon. Certain

details they reported differ markedly from the nesting habits and behavior that my colleagues and I observed for the

Barred Forest-Falcon (M. ruficollis) (Thorstrom et al. 2000a, Auk 117:781-786) and Collared Forest-Falcon (M. semi-

torquatus) (Thorstrom et al. 2000b, Ornithol. Neotrop. 11:1-12) in northern Central America, from 1988-96. These

differences are profound enough to suggest that the raptor species was possibly misidentified as a forest-falcon, or

that the Slaty-backed Forest-Falcon displays some rather uncommon behavior within the genus of Micrastur.

De Vries and Melo (2000) reported on 14 September, and again on 23 October 1997, that the nesting forest-

falcons had a changeover, implying an incubation and a brooding switch, respectively. I never recorded an incubation

or brooding switch during 8 breeding seasons of nest observations of Barred {N = 70 nesting attempts) and Collared

Forest-Falcons {N = 9 nesting attempts). For these two forest-falcons, the males’ role was providing food to the

incubating and brooding female and nestlings. During incubation, the male contact-called to the female upon his

arrival to the nest vicinity with prey, and the female exited the nest to receive the prey item where she ate it. Onrare occasions, the male entered the cavity while the female ate. The male stayed inside for several minutes either

incubating, attempting to incubate or to look at the nest contents, and then he exited the cavity prior to the female’s

return (Thorstrom 1993, M.S. thesis, Boise State University, Boise, ID U.S.A., Thorstrom et al. 2000a, Thorstrom et

al. 2000b).

De Vries and Melo (2000) suspected also that the female fed herself away from the nest and returned to take over

incubation or brooding from the male. This does not agree with my observations (Thorstrom et al. 2000a, Thorstrom

et al. 2000b) and those of Baker et al. (2000, Ornithol. Neotrop. 11:81-82). Only on very rare occasions did the female

leave the nest during incubation to feed herself when the male was late with a prey delivery and hunger brought her

off the nest (Thorstrom 1993).

De Vries and Melo (2000) describe an open nest constructed of small sticks and deep enough to hide the head

of the incubating Slaty-backed Forest-Falcon. In contrast, all described nests for the genus Micrastur have been mcavities (Mader 1979, Condor 81:320) and all nesting attempts by both Barred Forest-Falcons and Collared Forest-

Falcons observed by my colleagues and me in Central America were in tree cavities (Thorstrom et al. 1990, Condor

90:237—239, Thorstrom et al. 2000a, Thorstrom et al. 2000b) except the observation by Baker et al. (2000) of a pair

of M. ruficollis nesting in a cliff pothole below canopy level. There is also a record of a Collared Forest-Falcon nesting

in a ruined building (Cobb 1990, cited by Howell and Webb 1995, The birds of Mexico and Central America, Oxford

Univ. Press, New York, NYU.S.A.). There is one mention of stick nesting by the Lined Forest-Falcon (M. gilvicollis)

in del Hoyo et al. (1994, Handbook of the birds of the world, Lynx Edicions, Barcelona, Spain), but no details were

provided. Forest-falcons do appear to have some flexibility in their choice of nest sites, but they seem to prefer a site

that simulates a cavity; i.e., trees or cliff potholes surrounded by forests.

The Slaty-backed Forest-Falcon has several described calls: one is a 10-14 nasal aah syllables and another a two

part series '‘ah, ow, ow, ow, ow, ow, ow, uah, uah, uah, uah, uaK' (Ridgely and Gwynne 1989, A guide to the birds of

Panama, Princeton Univ, Press, Princeton, NJ U.S.A.), a chanting series 8-13 nasal, thus contrasting with the 6 calls

“kui kui kui kui kui kui' reported by de Vries and Melo (2000).

The authors’ example of the Monk Parakeet {Myiopsitta monachus), a cavity nester that builds a stick nest, does not

support their suggestion that the Slaty-backed Forest-Falcon is normally a stick nest builder. Also, their basis for

suspecting the forest-falcons built the nest is somewhat vague, i.e., “We did not see the nest being built so we did

not know if the falcons had taken an old nest made by another species, but we felt that this was unlikely because we

did not see the nest on our regular censuses” (de Vries and Melo 2000). In Central America, forest-falcons were

never observed constructing nests out of sticks or carrying nesting material (Thorstrom et al. 2000a, Thorstrom et

al. 2000b). However, it is quite possible that forest-falcons can occupy a previously-built nest in a situation that

replicates a cavity. There are six known species of Micrastur, and the Lined Forest-Falcon may represent two separate

species (A. Whittaker pers. comm.), which would make seven. Among these, two (M. ruficollis, M. semitorquatus) are

335

336 Letters VoL. 36, No. 4

known cavity nesters, three (M. plumbeus, M. gilvicollis, and the proposed new species) are suspected cavity nesters,

and for one nesting details are unknown (M. huxkl£yi). Thus, the report by de Vries and Melo (2000), stating that Mmirandollei is a stick builder and nester, contrasts sharply with the large body of evidence from its congeners.

De Vries and Melo (2000) seemed uncertain about their identification of the species they were observing on the

nest. They came to the conclusion that the birds they had observed were not Gray-bellied Goshawks {Accipiter polio-

gastei) because of the white belly and yellow facial area of the supposed female, and the other bird, the supposed

male, had buff below with both birds having long legs and three narrow, dirty white tail bands (de Vries and Melo

2000). I suggest that the characteristics that de Vries and Melo used to identify this nesting pair of raptors were not

conclusive and that they have misidentified this species. The Grey-bellied Goshawk has dark back and crown, long

yellow legs, white to gray belly and female larger than male (del Hoyo et al. 1994). Accipiters have long legs, faint

tail bands, and females are larger than males. The size dimorphism was commented on by the authors “the first

falcon was smaller and probably the male of the pair.” Sexual size dimorphism of forest-falcons was very difficult to

distinguish in the field (pers. observ.) because they are only slightly to moderately dimorphic (Thorstrom 1993). Size

dimorphism is also a characteristic described for the Grey-bellied Goshawk and Bicolored Hawk {Accipiter bicolor) (del

Hoyo et al, 1994). The authors did not give any further detailed characteristics of the color of the legs, back, eyes,

and crown of the nesting raptors. The nesting behavior and habitat, vocalization, and plumage characteristics suggest

lhat the nesting birds described by de Vries and Melo (2000) were possibly accipiters, either the Crrey-bellied Goshawkor Bicolored Hawk.

I thank The Peregrine Fund for support and L. Kiff, R. Bierregaard, J. Bednarz, and one anonymous reviewer for

their comments on this manuscript.—Russell Thorstrom, The Peregrine Fund, 5668 West Flying Hawk Lane, Boise,

ID 83709 U.S.A.; E-mail address: [email protected]

Received 21 August 2001; accepted 19 June 2002

/. RaplorRes. 36(4);337


Micrastur or Accipiter, That is the Question

. . the more you look the more you see” (Peter Grant 1986, Ecology and evolution of Darwin’s finches. Princeton

Univ. Press, Princeton, NJ U.S.A.).

The main point made by Thorstrorn (2002, J. Raptor Res. 36:335-336) concerns the behavior of our birds, which

he claims is not the behavior of Micrastur (he should perhaps say the behavior of M. ruficollis and M. semilorquatus,

as the behavior of the other four species is still unknown) . We can report that the Slaty-backed Forest-Falcon {Micrastur

mirandolld) was present in the area of its now defunct 1997 stick nest (de Vries and Melo 2000,/ Raptor Res. 34:148-

150) in March of 1998. Although we cannot be sure that it is the same bird we saw previously at and around the

nest, it responded (vocalized, but did not come out into the open) to the species’ call as recorded by John Mooiem his series of bird sounds of eastern Ecuador. So far, we have been unable to locate its new nesting site.

The Grey-bellied Goshawk {Accipiter poliogaster) was present at some 5 km distance from the MicrasturncA site in

both 1997 and 1998. We observed this species in the more open and bare branches of the canopy, rather than the

densely-vegetated, middle canopy layer, where we noted Micrastur mirandollei.

We hope that the comment by R. Thorstrorn (2002) stimulates more observations on Micrastur, which are badly

needed. In addition, further study on why some avian raptors are so similar in plumage patterns, as is the case with

M. mirandollei and Accipiter poliogastca; would be valuable in understanding the potential adaptive benefits of such

“mimicry.” In our field experience, the “capped” appearance and tail banding oi Accipiter 'Are diagnostic, as are the

round grey head and yellow face that Micrastur features.

—

Tjitte de Vries and Cristian Melo, Departamento de Biol-

ogia, Pontificia Universidad Catolica del Ecuador, Apartado 17-01-2184, Quito, Ecuador; E-mail address: tdevries@

puceuio.puce.edu.ee

Received 8 November 2001; accepted 27 June 2002

337

BOOK REVIEWS

J Raptor Rf,s. 36(4) :338


Birds of Prey; Health 8c Disease. By John E.

Cooper. 2002. 3rd edition. Blackwell, Oxford,

U.K. xvii + 345 pp., 13 tables, 56 figures, 28 color

plates, 11 appendices. ISBN 0-632-05115-9. Hard-

back, £59.50.—The study of raptors is unquestion-

ably enhanced by the diversity of perspectives from

which it derives, i.e., from biologists, falconers,

medical practitioners, and others. Each of these

disciplines provides data and references that ad-

dress birds of prey in unique and relevant terms.

In updating his earlier pioneering work, Vetmnary

Aspects of Captive Birds of Prey, now entitled Birds of

Prey: Health & Disease, John Cooper continues his

intentionally eclectic collection of information and

points-of-view. The new work is organized identi-

cally to the former but for the addition of three

new chapters from contributing authors. Roughly

one-third of the information in the new book is

repeated verbatim from the earlier one, one-third

includes previous information updated by a brief

summary of advancements and a list of references

for further study, and the remainder is an expan-

sion that reflects work that has appeared since the

earlier volume.

Cooper has long advocated collaboration amongall who deal with birds of prey, which is borne out

by his approach to the new addition. Cooper is at

once observer, historian, and medical practitioner

in discussing the various topics. He makes no at-

tempt to cover the subjects in depth, but rather

provides context and references for the reader’s

use. The diverse array of topics, and the somewhat

lack of in-depth coverage, may serve as a disap-

pointment to some but will be acceptable to others

as an interesting and general guide. The value of

the book will certainly be defined by the expecta-

tions of those who use it.

The contributed chapters vary considerably in

scope and detail. Paolo Zucca’s chapter on anato-

my is generalized with varying degrees of detail.

Once again, subjectivity is a factor in some conclu-

sions. Ian Newton’s discussion of parasitic diseases

IS, by nature, broad, yet is thorough and sound in

content. The late David Peakall’s contribution re-

garding poisonings in free-living raptors is an in-

clusive general overview of chemical toxicity on a

worldwide scale.

This is an intensely personal work. Cooper states

emphatically that he has laced the writing with

opinions, personal experiences, and other subjec-

tive matter. One of the most difficult challenges in

reviewing this work is to assign it to a category for

the reader. The book is not a clinical manual, nor

a biology text, nor a handbook for falconers. It

does, however, contain elements of each along with

personal reflections on the experiences and opin-

ions of the principal author. Although resisting

classification. Birds of Prey: Health & Disease fills a

useful and interesting niche in raptor literature for

all those involved in the field.

—

James D. Elliott,

South Carolina Center for Birds of Prey, P.O. Box1247, Charleston, SC 29402 U.S.A.

J. Raptor Res. 36(4):338-339


Owls. By Floyd Scholz. 2001. Stackpole Books,

Mechanicsburg, PA. xiii + 379 pp., more than 700

color photographs. ISBN 0-8117-102T1. Cloth,

$80.00.—In 1993, Floyd Scholz published Birds of

Prey, which was a collection of detailed color pho-

tographs of 17 species of North American falconi-

forms (see /. Raptor Res. 28:278—279, 1994). Team-

ing up once more with photographer Tad Merrick,

Scholz has expanded his domain to include the

strigiforms. The result is an extensive series of col-

or photographs of 17 of the 19 species of owls

(Western Screech-Owl \_Otus kennicottii] and Whis-

kered Screech-Owl [O. trichopsis] omitted) that

breed in the United States and Canada.

Floyd Scholz is an extraordinary carver and

painter of birds, and the main purpose of Owls is

to serve as a reference guide for artists. An intro-

338

December 2002 Book Reviews 339

ductory chapter, “What is an Owl?” presents infor-

mation on the various morphological adaptations

of owls; the treatment enhances the text and is ba-

sically the same as that found in any coffee table

book or general ornithology text that deals with

owls. The species accounts make up the heart of

the book. Each includes a page of information on

morphology and behavior of the species in ques-

tion, details on the size of various body parts (in-

cluding line drawings of the species from the back

and side), and numerous color photographs (typ-

ically 30-40 per species). The photos are taken

from nearly every conceivable angle to provide de-

tails on plumage, talons, ear tufts, facial ruffs, eyes,

bills, nostrils, and napes, to name but a sample of

the features depicted. These photos contain fine

points that would seldom be noticed without hav-

ing a bird in the hand and thus will serve as a

valuable reference for people who do not have ac-

cess to museum specimens. Most of the photos are

of captive birds, the exceptions being a handful of

very nice shots of wild Northern Hawk Owls (Sur-

nia ulula)

,

Great Gray Owls {Strix nebulosa), and

Boreal Owls {Aegolius funereus) by Ron Austing and

Robert Taylor.

The photo selection, and the photos themselves,

are truly excellent, but two criticisms are worth

mentioning. First, the Great Horned Owl {Bubo vir-

ginianus) shown in many of the photos can be

readily described by two words: pissed off. Tm not

sure why an artist would need photos of an owl in

this state, nor why someone would continue to

bother a bird that so obviously detested whatever

treatment it was receiving. In fairness to the author

and photographer, this same attitude is displayed

by a wild female Great Horned Owl depicted onthe cover of the Birds of North America species ac-

count. Second, I was surprised that none of the 32

photos of the two species of pygmy-owls contained

a decent view of the so-called “false eyes” on the

back of the head. This is a minor quibble to be

sure, but an opportunity missed nonetheless.

The last two chapters are entitled “Techniques

for the Artist and Garver” and “Gallery,” the latter

consisting of a collection of photos of some of the

owls Mr. Scholz has carved and painted. The carv-

ings are absolutely gorgeous and point to the enor-

mous talent of the author. This book will appeal to

anyone with an interest in owls, although the price

may place it out of reach of all but the confirmed

“owlaholics,” to borrow a phrase coined by HeimoMikkola.

—

Jeff Marks, Montana Cooperative Wild-

life Research Unit, University of Montana, Missou-

la, MT 59812 U.S.A.

J Raptor Res. 36(4);340—343


Journal of Raptor Research

INFORMATION FOR CONTRIBUTORS

The Journal of Raptor Research (JRR) publishes

original research reports and review articles about

the biology of diurnal and nocturnal birds of prey.

All submissions must be in English, but contribu-

tions from anywhere in the world are welcome.

Manuscripts are considered with the understand-

ing that they have not been published, submitted

or accepted for publication elsewhere. Manuscripts

are subjected to peer review for evaluation of their

significance and soundness, and edited to improve

communication between authors and readers. De-

cisions of the editor are final.

Material is published as feature articles, short

communications (usually not longer than four

printed pages), and letters (see recent issue of the

JRR for examples) . Submissions that adhere closely

to the JRR’s format greatly enhance the efficiency

and cost of the editorial and publishing processes.

Author’s efforts in this regard are deeply appreci-

ated by the editorial staff.

When submitting scholarly papers, send the orig-

inal and three copies, a completed checklist (see

below), and a cover letter that includes: (1) a state-

ment that the data in the manuscript have not

been published or accepted for publication in the

same form, and have not been submitted simulta-

neously elsewhere, (2) the name and address of

the corresponding author (in multiauthored pa-

pers) including any temporary addresses where

that author will be during the review process (also

the phone number and, if possible, a FAX numberand e-mail address of the corresponding author),

and (3) if applicable, any special instructions. Au-

thors may also suggest potential reviewers.

If the manuscript submitted was produced on a

word processor, also send a diskette (3 1/2") con-

taining a single hie that is identical with the print-

ed copy. The electronic copy should be supplied

as an IBM-compatible text hie (ASCII, Word, or

WordPerfect). Include information on the type of

computer and word processor used. Optional elec-

tronic submissions are accepted (see General In-

structions below)

.

Manuscripts that are accepted upon condition of

revision must be returned to the editor within 60

days. Manuscripts held longer will lose their pri-

ority and may be treated as new submissions. Theeditor should be notihed if extenuating circum-

stances prevent a timely return of the manuscript.

Authors will receive proofs of their articles prior to

publication. Proofs must be read carefully to cor-

rect any printer errors and returned by the fastest

mail within two days of receipt TO THE EDITOR.Changes in typeset text are expensive and authors

making extensive changes will be billed for the

costs. A reprint order will accompany page proofs

to enable authors to buy reprints. Costs of reprints

are the author’s responsibility and payment for re-

prints ordered must accompany the order form.

Both must be sent TO THE EDITOR.Publication is expensive and member dues do

not cover the entire cost of producing the JRR.

Hence, the Raptor Research Foundation, Inc. ex-

pects that authors defray the high costs of publi-

cation through payment of page costs (currently

$100.00 EI.S. per page). Authors who are not as-

sociated with a research institution or simply do

not have access to such grants may request the

page charges be waived. Such a request can only

be approved if the author is a member of the Foun-

dation and the article is short. Payments of

amounts less than the full page charges will be ac-

cepted. Authors of long manuscripts are expected

to pay publishing costs. It is unlikely that articles

longer than 10 printed pages or 18 typewritten

pages including tables and illustrations can be pub-

lished without full payment. Authors employed by

government agencies, univer.sities, or hrms that

will meet reprint and page charges may forward a

statement to the editor indicating intent to pay.

Upon receipt of such a statement, reprints will be

mailed to the author and the agency will be billed

with the understanding that payment will be madewithin 30 days. All checks should be made payable

to the Raptor Research Foundation, Inc. All per-

sonal payments toward publication costs are tax-

deductible in the United States.

340

December 2002 Information for Contributors 341


CHECKIJST FOR PREPARATION OF MANUSCRIPTS{check items and submit with manuscript)

I. General Instructions

(Consult recent issues for additional guidance on format)

I I Type manuscripts on one side of either 216 X 278

mm (8.5 X IT') or standard international size (210

X 297 mm) good quality paper (do not use erasable

or lightweight paper). Word-processor-generated

manuscripts must be done with a letter-quality or near-

letter-quality printer. DOUBLE SPACE THROUGH-OUT including title, text, tables, hgure legends, andliterature cited.

Optional electronic submission. Submit e-mail mes-

sage with two attached file copies of manuscript: 1)

pdf hie (must include hgures) and 2) word processing

hie (Word Perfect [preferred] or MS Word hies ac-

cepted). Follow same format guidelines as for stan-

dard mail submission. Letter of transmittal should be

included in the e-mail message. E-mail to; jrr@astate.

eduGive the scientihc name at the hrst mention of a spe-

cies, both in the abstract and in the article. Scientihc

names of birds should follow the usage of the AOUCheck-list of North American Birds (7th. ed. 1998 andsubsequent supplements in the Auk) or an authorita-

tive source corresponding to other geographic re-

gions. Do not give subspecihc identihcation unless it

is pertinent. Capitalize hrst letter of words in com-

plete common names for birds. Use lower case for all

other common names.

D Use American spelling and Webster’s Tenth New Colle-

giate Dictionary (1996, Merriam-Webster, Inc.) as a

spelling authority.

Leave at least a 25 mm (1") margin on all sides. Avoid

hyphens or dashes at ends of lines; do not divide a

word at the end of a line.

Use a nonproportional font of at least elite size (4.7

characters/cm = 12 characters/inch) or 12 point,

preferably Courier. DO NOT USE RIGHT JUSTIFI-

CATION-LEAVE RIGHT MARGIN RAGGED.D Use italic type for addresses, scientihc names, journal

names, and third level headings.

Type last name(s) of author (s) and page number in

upper right-hand corner of page 2 and all following

pages.

Cite each hgure and table in the text. Do not repeat

material in two forms (i.e., in text and table, or table

and hgure). Organize text, as far as possible, so that

tables and hgures are cited in numerical order.

Use “Figure” only to start a sentence; otherwise

“Fig.” if singular, “Figs.” if plural (e.g.. Fig. 1; Figs. 2,

3; Figs, d—6).Use metric units throughout.

Use these abbreviations without spelling out: hr, min,

sec, yr, mo, wk, d, km, cm, mm; designate temperature

as 32°C.

Use “continental” dating (e.g., lOJuly 1993, l-3June,

11 May to 11 June).

Use 24-hour clock (e.g., 0800 H, 1345-1400 H)Write out numbers one to nine unless a measurement(e.g., four birds, 3 km, 40 sites, 6 yr). Use 1000 and10 000; 0.15 instead of .15; % instead of percent.

Each reference cited in text must be listed in the Lit-

erature Cited section, and vice versa. Double check

the accuracy of all entries-—THE EDITORIAI. STAFFCANNOT DO THIS FOR YOU.Literature citations in the text are as follows;

a. One author-Jones (1993) or (Jones 1993)

b. Two authors-Smith and Jones (1991) or (Smith

and Jones 1991)

c. Three or more authors-Hernandez et al. (1990) or

(Hernandez et al. 1990)

d. Manuscripts accepted for publication but not yet

published-Howard (in press) or (Howard in press)

e. Unpublished materials-K. Jacobson (unpubl.

data); (K. Jacobson pers. comm.); or K. Jacobson

(pers. comm.)-do not place in the Literature Cited

section.

f. When citing several references within parentheses,

separate with commas and put in chronological or-

der, olde.st hrst).

g. For manuscripts submitted as letters, place cita-

tions in text in abbreviated form, e.g., (I.C. Birds

1993, J. Raptor Res. 27:45-50).

Assemble manuscripts for regular articles in this or-

der: (1) title page, (2) abstract page, (3) text, (4) ta-

bles, (5) hgure legends, (6) hgures. DO NOT STA-

PLE.

II. Title Page

Place full title 6-8 lines below top of page in all

capital letters. Below title, center author’s

name(s) in all capital letters and address (es)

followed by a running title (short title) not to

exceed 30 characters. If the author(s) is/are

currently at another location from where the

work was done, use superscript number (s) fol-

lowing author (s) name(s) to indicate current

address in footnote at bottom of the page. In

multiauthored papers, indicate the author re-

sponsible for correspondence and requests for

reprints. Give phone number and, if possible,

FAX number and e-mail address of the corre-

sponding author.

III. Abstract/summary

For regular articles, include an abstract of about

250 words in one paragraph that is completely

342 Information for Contributors VoL. 36, No. 4

without reference to the text. Be concise, in-

clude the paper’s purpose, but emphasize the

results. Statements like “results will be dis-

cussed” are not appropriate. The abstract will

also be published in Spanish. Authors fluent in

both languages are encouraged to include both

versions, otherwise the JRR will provide the

Spanish translation.

Include hve to seven key words for indexing af-

ter the abstract.

Short communications will be printed with a

Spanish summary only. Authors must provide

an English summary to be translated into Span-

ish unless they are fluent in Spanish.

Avoid citing references in the abstract. If they

must be cited, include journal name, volume,

pages, and year, all in parentheses.

IV. Text

Follow instructions in section I.

Main headings are all capital letters and flush

with left margin,

n Typical main headings for regular articles are:

METHODS, RESULTS, and DISCUSSION. Anintroduction begins the text but does not have

a heading.

Put second-level headings in bold. Use normalindentation and capitalize first letter of each

word in the second-level headline except prep-

ositions and articles.

n Put third-level headings in italics. Capitalize first

letter of first word only.

Short communications and letters may or maynot have headings within the text dependingupon the need.

V. Literature Cited

Type references in upper and lower case letters,

including all authors’ names (e.g., Nemeth,N.M, and J.L. Morrison. 2002. Natal dispersal of

the Crested Caracara . . . etc. . . .).

Verify all entries against original sources includ-

ing diacritical marks and spelling in languages

other than English. Capitalize all nouns in Ger-

man,

Cite references in alphabetical order by first au-

thor’s surname. References by a single author

precede multiauthored works by the same se-

nior author regardless of date.

List works by the same author (s) chronologi-

cally, beginning with the oldest.

Use six hyphens when the author is the sameas in the preceding citation.

“In press” citations must have been accepted

for publication and must include date, volumenumber, and the name of the journal or pub-

lisher.

Initials of second, third, and. . . authors precede

their surname.

Abbreviate journal names according to the Se-

rial Sources for the BIOSIS Data Base (published

annually by the BioSciences Information Ser-

vice) .

Do not list personal communications and un-

published reports.

VI. Tables

(Tables are expensive to print-keep them to a min-

imum and put each on a separate page-try to de-

sign them to fit a single column.)

Double space throughout. Assign each table an

Arabic number followed by a period.

Table titles must be complete sentences.

Use same size of type as in text.

Indicate footnotes by lowercase superscript let-

ters.

Do not use vertical lines.

VII. Figure Legends

Print all figure legends on one page, double

spaced.

Number using Arabic numbers consecutively in

the same order the hgures appear in the text

(i.e.. Figure 1., Figure 2., etc.).

VIII. Preparation of Illustrations

(Illustrations are referred to as figures and include

drawings, graphs, and black and white half-tones

[photographs] . CONSULT THE EDITOR IN AD-VANCE ABOUT COLOR.)

Use professional standards in preparing figures,

their reproduction in the JRR is virtually iden-

tical to what is submitted. Consult issues ofJRRfor examples and Steps Toward Better Scientific Il-

lustrations (Allen Press, PO. Box 368, Lawrence,

KS 66044) for more information.

Plan figures to fit proportions in the JRR, pref-

erably for a single column-printed size is 72

mm for single column width, 148 mm for full

page width or 195 mm for lengthwise figures.

Figures should be submitted no smaller than

the final size nor larger than twice the final size

(on paper no larger than 216 X 278 mm (8.5

December 2002 Information for Contributors 343

X 11") or standard international (210 X 297

mm).Submit drawings as original art (undiluted In-

dia ink on heavy-weight, smooth-finish drafting

paper) or as photomechanical transfers

(PMTs). Submit graphs as mechanical drawings

or as high-resolution laser prints. Typed or

handwritten text or symbols are not acceptable.

Add text and symbols with press-on symbols and

letters or mechanical lettering. Review copies of

figures can be photographic copies but must ap-

proach the quality of the original.

Figure text must be a plain (sans serif) typeface

(e.g., Helvetica), not compressed, and large

enough so that it will be as large as the text type

(8-10 point) when in print.

Photographs must be sharp, high-contrast,

glossy prints approximately the size that they

will appear in print. If several photographs are

to be included in one figure, group them butt-

ed together with no space between.

Use the same style of lettering and presentation

for all figures.

IX. What to Send

Cover letter.

Copy of this checklist completed.

Original and three copies of manuscript and il-

lustrations.

Diskette containing a text file of the manuscript

text, tables, and figures (if the manuscript was

prepared using a word processor)

.

D Submit to:

James C. Bednarz, Editor


Department of Biological Sciences

P.O. Box 599, 117 Caraway RoadArkansas State University

State University, AR 72467 U.S.A.

More information?

Telephone: (870) 972-3082

FAX: (870) 972-2638

E-mail: [email protected]

J RaplorRes. 36(4):M4-350


Index to Volume 36

By Kristina Baker

This index includes references to general, species, common names, key words, and authors. Reference is also madeto book reviews, letters, and reviewers. Taxa other than raptors are included where referenced by authors.

A

Abuladze, Alexander and Jevgeni Shergalin, The Golden

Eagle in north Caucasia and Transcaucasia, 10-17

(suppl.)

Afdpiler, 229-230

(ooperii 229-230

gentilis, 141-143, 229-230, 265-279

sLriaius, 229-230

Aegolius funereus, 2 1 8—2 1

9

Age differences, 115-120

Agostini, Nicolantonio, Luca Baghino, Charles Coleiro,

Ferdinando Corbi, and Guido Premuda, Circuitoxis

autumn migration in the Short-toed Eagle { Circaetus

gallicus), 111-114

Alaska, 50-54 (suppl.)

Albinism, 200-202

Alloparental care, 70-73

Ammer, Frank K. and Petra Bohall Wood, Probable

breeding of Short-eared Owls in southern West Vir-

ginia, 237-238

Andersen, David E., see Warnke, D. Keith

Anderson, David L., see Thorstrom, Russell

Angulo, Elena, Factors influencing length of the pc^st-

fledging period and timing of dispersal in Bonelli’s

Eagle {Hieraaetus fasciatus) in southwestern Spain,

157

Anthropogenic food sources, 220-224

Aparicio, Jose, see Cordero, Pedro J.

Apodaca, Christine K., see Seavy, Nathaniel E.

Aquila dirysaetos, 3-9 (suppl.), 10-17 (suppl.), 18-19

(suppl.), 20-24 (suppl.), 25-28 (suppl.), 29-31



(suppl.)

xvahlbergi, 51—57

Argentina, 206-212, 315-319

Asia otus, 73-77

Athene cunicularia Jloridana, 3-10

Avila, Gregorio Lopez, see Whitacre, David F.

Avila, Juventino Lopez, see Whitacre, David F.

Avery, Michael L., John S. ITiimphrey, Eric A. Tillman,

Kimberly O. Phares, and Jane E. Hatcher, Dispersing

vulture roosts on communication towers, 45-50

Ayers, Serena, see Thorstrom, Russell

B

Baghino, Luca, see Agostini, Nicolantonio

Bainbridge, Ian R, see McGrady, Michael J.

Baja California Peninsula, 3-9 (suppl.)

Baker, Aaron, see Thorstrom, Russell

Balbontin, Javier and Miguel Ferrer, Plasma chemistry

reference values in free-living Bonelli’s Eagle {Hi-

eraaetus fasciatus) nestlings, 231-235

Bald and Golden Eagle Protection Act, 29-31 (suppl.)

Band, encounters, 97-110

recoveries, 97-110

Barry, Irene M., see Powell, Larkin A.

Barton, Nigel W.H., Nicholas C. Fox, Peter F. Surai, and

Brian K. Speake, Vitamins E and A, carotenoids, and

fatty acids of the raptor egg yolk, 33-38

Bates, John M., see Grifliths, Carole S.

Bats, 146-148

Beasom, Sam. L, see Proudfoot, Glenn A.

Bechard, MareJ. and Michael J. McGrady, Status and con-

servation of Golden Eagles, 2 (suppl.)

Bednarz, James C., Working toward excellence, 1-2

Behavior, 77-81, 121-127, 136-139

copulation, 66-70

hunting, 194-199

ranging, 70-77 (suppl.)

Beheim, Janne, Katrine Eldegard, Gro Bj0rnstad, Mats

Isaksson, Geir Sonerud, Olav Heie, and Helge

Klungland, DNA polymorphisms in Boreal Owls {Ae-

golius funereus) ,2 1 8—2 1

9

Bellocq, M. Isabel, Patricio Ranhrez-Llorens, andjulieta

Filloy, Recent records of Crowned Eagles {Harpyhal-

iaetus coronalus) from Argentina, 1981-2000, 206-

212

Berkelman, James, James D. Fraser, and Richard T. Wat-

son, Nesting and yjerching habitat use of the Mada-

gascar Fish-Eagle, 287-293

Bertram, Joan and Antoni Margalida, Social organization

of a trio ol Bearded Vultures {Gypaetus barbatus): sex-

ual and parental roles, 66-70

Bianchi, Edward W., see Hunt, W. Grainger

Bias, 11-16

Bildstein, Keith 1.., sec Yosef, Reuven

Bj0rnstad, Gro, see see Beheim, Janne

Blood, 231-235

parasites, 139-141

Bloxton, Thomas D., Audi Rogers, Michael F. Ingraldi,

344

December 2002 Index to Volume 36 345

Steve Rosenstock, John M. Marzluff, and Sean RFinn, Possible choking mortalities of adult Northern

Goshawks, 141-143

Boano, Giovanni and Roberto Toffoli, A line transect sur-

vey of wintering raptors in the western Po Plain of

northern Italy, 128-135

Bogliani, Giuseppe, see Sergio, Fabrizio

Bolivia, 146-148

Boto, Alberto, see Sergio, Fabrizio

Brazil, 328-331, 332-334

Breeding, 161-169

diet, 332-334

season, 194-199

success, 24-32, 81-84, 224-228

Brendel, Ulrich M., Rolf Eberhardt, and Karen Wies-

mann, Conservation of the Golden Eagle (Aquila

chrysaetos) in the European Alps—a combination of

education, cooperation, and modern techniques,

20-24 (suppl.)

Bubo bubo, 11-16

virginianus, 58—65

Buhay, Jennifer E. and Gary Ritchison, Hunting behavior

of and space use by Eastern-Screech Owls during the

breeding season, 194—199

Buteo buteo, 24-32, 115-120, 128-135, 188-193

lineatus, 152-153

C

Calvert, Dan J., see Powell, Larkin A,

Canada, 32-40 (suppl.)

Canary Islands, 17-23

Cannibalism, 200-202

Capote, Nieves, see Donazar, Jose Antonio

Capture, 188-193

techniques, 320-323

Caracara cheriway, 203—206

Carpathian Mountains, 25—28 (suppl.)

Carrion, 152-153

Caryospora hutzeri, 84—86

Cathartes aura, 45-50, 144—145

burrovianus, 183-187

melambrotus, 183-187

Caucasia, 10-17 (suppl.)

Ceballos, Olga, see Donazar, Jose Antonio

Central America, 39-44

Chavez-Ramirez, Felipe, see Proudfoot, Glenn A.

Chihuahua, 3-9 (suppl.)

Chile, 315-319

Choking, 141-143

Circaetus gallicus, 111-114

Cliffs, 39-44

Coahuila, 3-9 (suppl.)

Coccidiosis, 84—86

Coleiro, Charles, see Agostini, Nicolantonio

Colonization, 18-19 (suppl.)

Colorado, 256-264

Columbretes Islands, 139-141

Common Buzzard, 24—32, 115-120, 128-135, 188-193

Communication tower, 45-50

Conservation, 10-17 (suppl.), 20-24 (suppl.), 29-31

(suppl.), 41-49 (suppl.), 51-57, 206-212

Constraints, 41-49 (suppl.)

Control region, 17-23

Cooke, Raylene, Robert Wallis, and John White, Use of

vegetative structure by Powerful Owls in outer urban

Melbourne, Victoria, Australia—implications for

management, 294-299

Coragyps atratus, 45-50

Corbi, Charles, see Agostini, Nicolantonio

Cordero, Pedro J., Jose M. Aparicio, and David T. Parkin,

Genetic evidence of alloparental care of a female

Lesser Kestrel in an alien nest, 70-73

Coulson, Jennifer O., Mississippi Kites use Swallow-tailed

Kite nests, 155—156

Crested Caracara, 203-206

Cromrich, Lee A., Denver W. Holt, and Shawne M. Lea-

sure, Trophic niche of North American Great

Horned Owls, 58-65

Culver, Melanie, see Tingay, Ruth E.

Cumulative impacts, 55-61 (suppl.)

Cytochrome b, 183-187

D

Dams, 245-255

de Vries, Tjitte and Cristian Melo, Micrastur or Accipiter,

that is the question, 337

Deforestation, 51-57

Degraaf, Richard M., see Smith, Harvey R.

Demography, 3-10

Denali National Park, 50-54 (suppl.)

Density, 24—32

Development, 3-10, 77-81

Dho-gaza, 320-323

Diet, 24-32, 58-65, 148-152, 328-331

assessment methods, 11-16

Dispersal, 176-182, 309-314

natal, 203—206

roost, 45-50

Distribution, 10-17 (suppl.)

Disturbance, 294—299

DNA, fingerprinting, 280-286

mitochondrial, 17—23

multilocus fingerprinting, 70-73

polymorphisms, 218-219

Donazar, Jose Antonio, Juan Jose Negro, Cesar Javier Pa-

lacios, Laura Gangoso,Jose Antonio Godoy, Olga Ce-

ballos, Fernando Hiraldo, and Nieves Capote, De-

scription of a new subspecies of the Egyptian Vulture

(Accipitridae: Neophron percnopterus) from the Canary

Islands, 17-23

Driscoll, Daniel E., see Hunt, W. Grainger

Durango, 3-9 (suppl.)

346 Index to Volume 36 VoL. 36, No. 4

Dykstra, Cheryl R., Michael W. Meyer, and D. Keith Warn-

ke, Bald Eagle reproductive performance following

video camera placement, 136-139

Dykstra, Cheryl R., see Warnke, D. Keith

E

Eagle, Bald, 29-31 (suppL), 121-127, 136-139, 161-169,

245-255, 256-264, 324-327

Bonelli’s, 231-235

Crested, 77-81

Crowned, 206-212

Crowned Hawk-, 300—308

Golden, 3-9 (suppL), 10-17 (suppL), 18-19 (suppl.),

20-24 (suppl.), 25-28 (suppl.), 29-31 (suppl.),

32-40 (suppl.), 41-49 (suppl.), 50-54 (suppl.),

55-61 (suppl.), 62-69 (suppl.), 70-77 (suppl.)

Long-crested, 51-57

Madagascar Fish-, 280-286, 287-293, 309-314

Short-toed, 111-114

Wahlberg’s, 51-57

White-tailed Sea, 220-224

Eberhart, Rolf, see Brendel, Ulrich M.

Effigy, 45-50

Eggs, 324-327

yolk, 33-38

Eggshell characteristics, 324-327

Elat, 115-120

Eldegard, Katrine, see Beheim, Janne

Elliot, James D., A review of Birds of Prey: Health & Dis-

ease, by John E. Cooper, 2002, 338

Elhs, David H., Beth Ann Sabo, James K. Fackler, and

Brian A. Millsap, Prey of the Peregrine Falcon {Falco

peregtinus cassini) in southern Argentina and Chile,

315-319

Ellis, David H., Lynn W. Oliphant, and James K. Fackler,

Schizochromism in a Peregrine Falcon from Arizo-

na, 200-202

Emergent trees, 300-308

Englund, Judy Voigt, see Martell, Mark S.

Environmental education, 20-24 (suppl.)

European Alps, 20-24 (suppl.)

F

Fackler, James K., see Ellis, David H., 200-202

Fackler, James K., see Ellis, David H., 315-319

Fahler, Natalie A. and Lester D. Flake, Nesting of Long-

eared Owls along the lower Big Lost River, Idaho: a

comparison of 1975-76 and 1996-97, 73-77

Falco deiroleucus, 39-44

eleonorae, 139-141

naumanni, 70-73, 148-152

peregtinus, 176-182, 200-202, 203-217, 315-319

tinnunculus, 81—84, 84-86

Falcon, Eleonora’s, 139-141

Orange-breasted, 39-44

Pallid, 315-319

Peregrine, 176-182, 200-202, 213-217, 315-319

Fatty acids, 33-38

Feeding, 144-145, 152-153

habits, 224-228

Ferrer, Miguel, see Balbontin, Javier

Filloy, Julieta, see Bellocq, M. Isabel

Finn, Sean R, Daniel E. Varland, and John M. Marzluff,

Does Northern Goshawk breeding occupancy vary

with nest-stand characteristics on the Olympic Pen-

insula, Washington?, 265-279

Finn, Sean R, see Bloxton, Thomas D.

Firmanszky, Gabor, The status of the Golden Eagle {Aq-

uila chrysaetos) in Hungary, 18-19 (suppl.)

Flake, Lester D., see Fahler, Natalie A.

Flocking, 111-114

Florida, 3-10, 203-206

Flyways, 97-110

Food, 144-145

-niche breadth, 58-65

Foraging habitat, 220-224

Forestry, 24—32

Fox, Nicholas C., see Barton, Nigel W.H.

Fractures, 229-230

Framework, 41—49 (suppl.)

Fraser, James D., see Berkelman, JamesFraser, James D., see Tingay, Ruth E.

French, Thomas W., see Roth, Aaron J.

G

Gangoso, Laura and Cesar J. Palacios, Endangered Egyp-

tian Vulture {Neophron percnopterus) entangled in a

power line ground-wire stabilizer, 238-239

Gangoso, Laura, see Donazar, Jose Antonio

Genetics, 183-187

Gladdium brasilianum, 170-175

Godoy, Jose Antonio, see Donazar, Jose Antonio

Grant, Justin R., see McGrady, Michael J.

Great Lakes, 136-139

Griffiths, Carole S. and John M. Bates, Morphology, ge-

netics and the value of voucher specimens: an ex-

ample with Cathartes vultures, 183-187

Gypaetus barbatus, 66-70

H

Habitat, 287-293

management, 55-61 (suppl.)

preferences, 224-228

quality models, 20-24 (suppl.)

selection, 245-255

use, 51-57

Haliaeetus albicilla, 220-224

leucocephalus, 29-31 (suppl.), 121-127, 136-139, 161-

169, 245-255, 256-264, 324-327

vociferoides, 280-286, 287-293, 309-314

Hallerman, Eric M., see Tingay, Ruth E.

December 2002 Index to Volume 36 347

Harmata, Alan R., Vernal migration of Bald Eagles from

a southern Colorado wintering area, 256-264

Harpyhaliaetus coronatus, 206-212

Hatcher, Jane E., see Avery, Michael L.

Hawk, Cooper’s, 229-230

Red-shouldered, 152-153

Sharp-shinned, 229-230

Heie, Olav, see see Beheim, Janne

Hieraaetus fasciatus, 231-235

Hiraldo, Fernando, see Donazar, Jose Antonio

Hoffman, Stephen W., Jeff R Smith, and Timothy D.

Meehan, Breeding grounds, winter ranges, and mi-

gratory routes of raptors in the mountain west, 97-

110

Hokkaido, Japan, 220-224

Holt, Denver W., see Cromrich, Lee A.

Home range, 70-77 (suppL), 245-255

Homosexual matings, 66-70

Humphrey, John S., see Avery, Michael L.

Hungary, 18-19 (suppl.)

Hunt, W. Grainger, Ronald E. Jackman, Daniel E. Dris-

coll, and Edward W. Bianchi, Foraging ecology of

nesting Bald Eagles in Arizona, 245-255

I

Idaho, 73-77

Immobilization, 188-193

Ingraldi, Michael R, see Bloxton, Thomas D.

Injuries, 229-230

Isaksson, Mats, see Beheim, Janne

Italy, 11-16, 24-32, 128-135

J

Jackman, Ronald E., see Hunt, W. Grainger

Jacobs, Eugene A. and Glenn A. Proudfoot, An elevated

net assembly to capture nesting raptors, 320-323

Janovsky, Martin, Thomas Ruf, and Wolfgang Zenker,

Oral administration of tiletamine/zolazepam for the

immobilization of the Common Buzzard {Buteo bu-

teo), 188-193

Jenkins, M. Alan, Steve K. Sherrod, David A. Wiedenfeld,

and Donald H. Wolfe, Jr., Florida Bald Eagle {Hal-

iaeetus leucocephalus) egg characteristics, 324-327

Jones, Gwilym S., see Roth, Aaron J.

K

Karasov, William H., see Warnke, D. Keith

Kery, Marc, New observations of the Peregrine Falcon

{Falco peregrinus) in Peru, 213-217

Kestrel, Eurasian, 81-84, 84-86

Lesser, 70-73, 148-152

Klungland, Helge, see see Beheim, Janne

Kochert, Michael N. and Karen Steenhof, Golden Eagles

in the G.S. and Canada: status, trends, and conser-

vation challenges, 32-40 (suppl.)

Kopij, Grzegorz, Food of the l,esser Kestrel {Falco nau-

manni) in its winter quarters in South Africa, 148-

152

Krone, Oliver, Fatal Caryospora infection in a free-living

Juvenile Eurasian Kestrel {Falco tinnunculus)

,

84—86

L

land use, 55-61 (suppl.)

Landaeta, Carlos A., see Vargas, Julieta

Leasure, Shawne M., see Cromrich, Lee A.

Leucism, 200-202

Linda, Lomo, see Nunnery, Tony

Logistic regression, 265-279

Londei, Tiziano, The Fox Kestrel {Falco alopex) hovers,

236-237

Lophaetus occipitalis, 51-57

M

Madagascar, 287-293

Madders, Mike and Dave Walker, Golden Eagles in a mul-

tiple land-use environment: a case study in conflict

management, 55-61 (suppl.)

Malan, Gerard and Susanne Shultz, Nest-site selection of

the Crowned Hawk-Eagle in the forests of Kwazulu-

Natal, South Africa, and Tai, Ivory Coast, 300-308

Management, 20-24 (suppl.), 294—299

Manganaro, Alberto, see Salvati, Luca

Mangrove, 328-331

Marches!, Luigi, Paolo Pedrini, and Fabrizio Sergio, Bi-

ases associated with diet study methods in the Eur-

asian Eagle Owl, 11-16

Margalida, Antoni, see Bertran, Joan

Mark-recapture, 3-10

model, 176-182

Marks, Jeff, A review of Owls, by Floyd Scholz, 2001, 338-

339

Martell, Mark S., Judy Voigt Englund, and Harrison B.

Tordoff, An urban Osprey population established by

translocation, 91—96

Martinez-Abrain, Alejandro and Gerardo Urios, Absence

of blood parasites in nestlings of the Eleonora’s Fal-

con {Falco eleonorae), 139-141

Marzluff, John M., a review of The Spanish Imperial Ea-

gle, by Miguel Ferrer, 2001, 242-244

Marzluff, John M., see Bloxton, Thomas D.

Marzluff, John M., see Finn, Sean P.

Mating system, 280-286

Mays, Jody L., see Proudfoot, Glenn A.

McAllister, Kelly R., see Watson, James W.

McGrady, Michael J., Justin R. Grant, Ian P. Bainbridge,

and David R.A. McLeod, A model of Golden Eagle

{Aquila chrysaetos) ranging behavior, 62-69 (suppl )

McGrady, Michael J., see Bechard, MarcJ.

McGrady, Michael J., see McLeod, David R.A

McIntyre, Carol L., Patterns in nesting area occupancy

and reproductive success of Golden Eagles {Aquila

348 Index to Volume 36 VOL. 36, No. 4

chrysaetos) in Denali National Park and Preserve,

Alaska, 1988-99, 50-54 (suppl.)

McLeod, David R.A., D. Philip Whitfield, and Michael J.

McGrady, Improving prediction of Golden Eagle

{Aquila chrysaetos) ranging in western Scotland using

GIS and terrain modeling, 70-77 (suppl.)

McI.eod, David R.A., see McGrady, Michael J.

Mediterranean areas, 81-84

Meehan, Timothy D., see Hoffman, Stephen W.

Melo, Cristian, see de Vries, Tjitte

Mexico, 3-9 (suppl.)

Meyer, Michael W., see Dykstra, Cheryl R.

Meyer, Michael W., see Warnke, D. Keith

Microsatellite, 218-219

Migration, 97-110, 111-114

differential, 97-110

spring, 115-120

vernal, 256-264

Millar, Jody Gustitus, The protection of eagles and the

Bald and Golden Eagle Protection Act, 29-31

(suppl.)

Miller, Richard S., see Smith, Harvey R.

Millsap, Brian A., see Ellis, David H.

Millsap, Brian A., Survival of Florida Burrowing Owls

along an urban-development gradient, 3-10

Minnesota, 91-96

Mizera, Tadeusz, see Waclawek, Krzysztof

Monitoring, 32-40 (suppl.)

Morphnus guianensis, 77-81

Morrison, Joan L., see Nemeth, Nicole M.

Mortality, 32-40 (suppl.), 141-143

Mottajunior, Jose Carlos, Diet of breeding Tropical

Screech-Owls (Otus choliba) in southeastern Brazil,

332-334

Movements, 62-69 (suppl.)

N

Navigation, 111-114

Negro, Juan Jose, see Donazar, Jose Antonio

Nemeth, Nicole M. andjoan L. Morrison, Natal dispersal

of the Crested Caracara {Caracara cheriway) in Flori-

da, 203-206

Neofjhron percnopterus majormsis, 1 7-23

Nest, access, 300-308

helper, 280-286

tree, 287-293

Nest-site selection, 300-308

Nesting, 73-77

biology, 77-81

Nestlings, 77-81, 139-141

free-living, 231-235

Net, drop, 320-323

elevated, 320-323

mist, 320-323

New records, 206-212

Ntnox strenua, 294—299

North America, 58-65, 229-230

western, 97-110

Northern Goshawk, 141-143, 229-230, 265-279

Nunnery, Tony, Lomo Linda, and Mark R. Welford,

Barred Forest-Falcon {Micrastur ruficollis) predation

on a hummingbird, 239-240

O

Olfaction, 144-145

Oliphant, Lynn W., see Ellis, David H.

Olmos, Fabio, see Silva e Silva, Robson

Oral administration, 188-193

Orientation, 111-114

Osprey, 91-96, 328-331

Otus asio, 194-199

choliba, 332-334

Overstory depth, 265-279

Owens, Thomas E., see Watson, James W.

Owl, Barn, 146-148, 224-228

Boreal, 218-219

Burrowing, 3-10

Eastern Screech-, 194-199

Eurasian Eagle-, 11-16

Ferriginous Pygmy-, 170-175

Great Horned, 58-65

Long-eared, 73-77

Mechanical, 320—323

Powerful, 294-299

Tengmalm’s, 218-219

Tropical Screech-, 332-334

P

Palacios, Cesar Javier, see Donazar, Jose Antonio

Palacios, Cesar J., see Gangoso, Laura

Pandion haliaetus, 91-96, 328-331

Parental roles, 66-70

Parkin, David T, see Cordero, Pedro J.

Pedrini, Paolo, see Marches!, Luigi

Perch time, 194—199

tree, 287-293

Peru, 213-217

Pesticides, 324-327

Phares, Kimberly O., see Avery, Michael L.

Piscivory, 245-255

Plasma, 33-38

chemistry, 231-235

Poland, 25-28 (suppl.)

Polyandry, 280-286

cooperative, 66-70

Population restoration, 176-182

Post-fledging, length, 157

movement, 220-224

status, 161-169

Powell, Larkin A., Dan J. Calvert, Irene M. Barry, and

Lowell Washburn, Post-fledging survival and dispers-

Dec;ember 2002 Index to Voeume 36 349

al of Peregrine Falcons during a restoration project,

176-182

Pranty, Bill, Red-shouldered Hawk feeds on carrion, 152-

153

Pre-Alps, 24-32

Premuda, Guido, see Agostini, Nicolantonio

Prey, 141-143, 315-319

biomass, 332-334

size, 146-148

Productivity, 91-96, 161-169

Protozoa, 84-86

Proudfoot, Glenn A., Sam L, Beasom, Felipe Chavez-Ra-

mirez, and Jody L. Mays, Response distance of Fer-

ruginous Pygmy-Owls to broadcasted conspecific

calls, 170-175

Proudfoot, Glenn A., see Jacobs, Eugene A.

Provisioning, 121-127

R

Radio-tracking, 256-264

Radiotelemetry, 245-255

Rafanomezantsoa, Simon, Richard T. Watson, and Russell

Thorstrom, Juvenile dispersal of Madagascar Fish-Ea-

gles tracked by satellite telemetry, 309-314

Ramirez-Llorens, Patricio, see Bellocq, M. Isabel

Ranazzi, Lamberto, see Salvati, Luca

Range, 62-69 (suppl.)

model, 70-77 (suppl.)

use, 194-199

Raptor nutrition, 33-38

Raptors, 128-135

Recovery, 161-169

Repopulation, 25-28 (suppl.)

Reproduction, 50-54 (suppl.)

Reproductive performance, 136-139

Restani, Marco, A review of Raptors of the World, by

James Ferguson-Lees and David A. Christie, 2001,

241-242

Riparian, 73-77

Ritchison, Gary, see Buhay, Jennifer E.

Rivers, 245-255

Rodriguez-Estrella, Ricardo, A survey of Golden Eagles in

northern Mexico in 1984 and recent records in cen-

tral and southern Baja California Peninsula, 3-9

(suppl.)

Rogers, Andi, see Bloxton, Thomas D.

Rome, 224-228

Rosenstock, Steve, see Bloxton, Thomas D.

Roth, Aaron J., Gwilym S. Jones, and Thomas W. French,

Incidence of naturally-healed fractures in the pec-

toral bones of North American Accipiters, 229-230

Ruf, Thomas, see Janovsky, Martin

S

Sabo, Beth Ann, see Ellis, David H.

Salvati, Luca, Lamberto Ranazzi, and Alberto Manganaro,

Habitat preferences, breeding success, and diet of

the Barn Owl ( Tyto alba) in Rome: urban versus rural

territories, 224-228

Salvati, Luca, Spring weather and breeding success of the

Eurasian Kestrel {Falco tinnunculus) in urban Rome,Italy, 81-84

Saskatchewan, 256-264

Satellite telemetry, 309-314

Scandolara, Chiara, see Sergio, Fabrizio

Scavenging, 144-145

Schizochromism, 200-202

Scotland, 62-69 (suppl.)

Seavy, Nathaniel E. and Christine K. Apodaca, Raptor

abundance and habitat use in a highly-disturbed- for-

est landscape in western Uganda, 51-57

Sergio, Fabrizio, Alberto Boto, Chiara Scandolara, and

Guiseppe Bogliani, Density, nest sites, diet, and pro-

ductivity of Common Buzzards {Buteo buteo) in the

Italian pre-Alps, 24-32

Sergio, Fabrizio, see Marchesi, Luigi

Sex, 231-235

Shergalin, Jevgeni, see Abuladze, Alexander

Sherrod, Steve K., see Jenkins, M. Alan

Shiraki, Saiko, Post-fledging movements and foraging

habitats of immature White-tailed Sea Eagles in the

Nemuro Region, Hokkaido, Japan, 220-224

Shoreline, 297-293

Shrub cover, 265-279

Shultz, Susanne, see Malan, Gerard

Silva e Silva, Robson, and Fabio Olmos, Osprey ecology

in the mangroves of southeastern Brazil, 328-331

Simonetti, Javier A., see Vargas, Julieta

Smith, Harvey R., Richard M. DeGraaf, and Richard S.

Miller, Exhumation of food by Turkey Vulture, 144-

145

Smith, Jeff R, see Hoffman, Stephen W.

Solifugae, 148-152

Sonerud, Geir, see Beheim, JanneSonora, 3-9 (suppl.)

South Africa, 148-152

South America, 213-217

Spain, 66-70

Speake, Brian K., see Barton, Nigel W.H.

Status, 32-40 (suppl.), 206-212

Steenhof, Karen, A review of The Raptor Almanac, by

Scott Weidensaul, 2000, 87-88

Steenhof, Karen, see Kochert, Michael N.

Stephanoaetus coronatus, 300—308

Stinson, Derek, see Watson, James W.Subspecies, 17-23

Surai, Peter E, see Barton, Nigel W.H.

Survey, 39-44

broadcast, 170-175

roadside, 51-57

winter, 128-135

Survival, 3-10, 176-182

350 Index to Volume 36 VoL. 36, No. 4

T

Tea plantation, 51-57

Temperature, 294-299

Territoriality, 62-69 (suppl.)

Territories, 224-228

Thorstrom, Russell, Comments on the first nesting re-

cord of the nest of a Slaty-backed Forest-Falcon {Mi-

crastur mirandollei) in the Ecuadorian Amazon, 335-

336

Thorstrom, Russell, Richard Watson, Aaron Baker, Ser-

ena Ayers, and David L. Anderson, Preliminary

ground and aerial surveys for Orange-breasted Fal-

cons in Central America, 39-44

Thorstrom, Russell, see Rafanomezantsoa, Simon

Tiletamine, 188-193

Tillman, Eric A., see Avery, Michael L.

Time budgets, 121-127

Tmgay, Ruth E., Melanie Culver, Eric M. Hallerman,

James D. Fraser, and Richard T. Watson, Subordinate

males sire offspring in Madagascar Fish-Eagle {Hal-

iaeetus vociferoides) polyandrous breeding groups,

280-286

Toffoli, Roberto, see Boano, Giovanni

Tordoff, Harrison B., see Martell, Mark S.

Transect, 128-135

Translocation, 91-96

Tropical, 77-81

Tryjanowski, Piotr, see Yosef, Reuven

Tyto alba, 146-148, 224-228

U

Uganda, 51-57

Urban, habitats, 81-84, 224—228

wildlife, 91-96

wildlife management, 3-10

Urbanization, 294—299

Urios, Gerardo, see Martinez-Abrain, Alejandro

U.S., 32-40 (suppl.)

V

Vargas, Julieta, Carlos Landaeta A., and Javier A. Simo-

netti. Bats as prey of Barn Owls { Tyto alba) in a trop-

ical savanna in Bolivia, 146-148

Variability, 218-219

Varland, Daniel E., see Finn, Seair P.

Vegetation structure, 294-299

Video camera, 136-139

Vitamins, 33-38

Voucher specimens, 183-187

Vultures, 45-50

Bearded, 66-70

Egyptian, 17-23

Turkey, 144—145

Yellow-headed, 183-187

WWaclawek, Krzysztof and Tadeusz Mizera, The status of

the Golden Eagle {Aquila chrysaelos) in Poland, 25-

28 (suppl.)

Wallis, Robert, see Cooke, Raylene

Warnke, D. Keith, David E. Andersen, Cheryl R. Dykstra,

Michael W. Meyer, and William H. Karasov, Provi-

sioning rates and time budgets of adult and nestling

Bald Eagles at inland Wisconsin nests, 121-127

Warnke, D. Keith, see Dykstra, Cheryl R.

Washburn, Lowell, see Powell, Larkin A.

Washington, 161-169, 265-279

Watson, James W., Derek Stinson, Kelly R. McAllister, and

Thomas E. Owens, Population status of Bald Eagles

breeding in Washington at the end of the 20^’^ cen-

tury, 161-169

Watson, Jeff and Philip Whitfield, A conservation frame-

work for the Golden Eagle {Aquila chrysaetos) in Scot-

land, 41-49 (suppl.)

Watson, Richard, see Thorstrom, Russell

Watson, Richard T., see Berkelman, James

Watson, Richard T., see Rafanomezantsoa, Simon

Watson, Richard T., see Tingay, Ruth E.

Weather conditions, 81-84

Welford, Mark R., see Nunnery, Tony

Whitacre, David R, Juventino Lopez Avila, and Gregorio

Lopez Avila, Behavioral and physical development of

a nestling Crested Eagle {Morphnus guianensis)

,

77—

81

White, John, see Cooke, Raylene

Whitheld, D. Philip, see McLeod, David R.A.

Whitfield, Philip, see Watson, Jeff

Wiedenfeld, David A., see Jenkins, M. Alan

Wiesmann, Karen, see Brendel, Ulrich M.

Wildlife, habitat relationships, 265-279

management, 300-308

Wind energy, 55-61 (suppl.)

Winter quarters, 148-152

Wintering, 256-264

ecology, 328-331

Wisconsin, 121-127

Wolfe, Jr., Donald H., see Jenkins, M. Alan

Wood, Petra Bohall, see Ammer, Frank K.

Y

Yosef, Reuven, Piotr Tryjanowski, and Keith Bildstein,

Spring migration of adult and immature buzzards

{Buteo buteo) through Elat, Israel; timing and body

size, 115-120

Z

Zacatecas, 3-9 (suppl.)

Zemplen Mountains, 18-19 (suppl.)

Zenker, Wolfgang, see Janovsky, Martin

Zolazepam, 188-193

Zones, 41-49 (suppl.)

THE JOURNAL OF RAPTOR RESEARCHA QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.

(Founded 1966)

EDITOR IN CHIEFJames C. Bednarz

James R. Belthoff

Clint W. Boal

Joan L. Morrison

Juan Jose Negro

ASSOCIATE EDITORSMarco Restani

Ian G. WarrentinTroy I. Wellicome

BOOK REVIEW EDITORJeffrey S. Marks

CONTENTS FOR VOLUME 36, 2002

Number 1

Editor’s Page: Working Toward Excellence. James C. Bednarz 1

Survival of Florida Burrowing Owls Along an Urban-Development Gradient.

Brian A. Millsap 3

Biases Associated with Diet Study Methods in the Eurasian Eagle-Owl. Luigi

Marchesi, Paolo Pedrini, and Fabrizio Sergio 11

Description of a New Subspecies of the Egyptian Vulture (Accipitridae; Neo-

phron fercnopterus) FROM THE Canary Islands. Jose Antonio Donazarjuan Jose Negro,

Cesar Javier Palacios, Laura Gangoso, Jose Antonio Godoy, Olga Ceballos, Fernando Hiraldo, and

Nieves Capote 17

Density, Nest Sites, Diet, and Productivity of Common Buzzards {Bijteo buteo)

in the Italian Pre-Alps. Fabrizio Sergio, Alberto Boto, Chiara Scandolara, and Giuseppe

Bogliani 24

Vitamins E and A, Carotenoids, and Fatty Acids of the Raptor Egg Yolk. Nigel

W.H. Barton, Nicholas C. Fox, Peter F. Surai, and Brian K. Speake 33

Preliminary Ground and Aerial Surveys for Orange-breasted Falcons in Central

America. Russell Thorstrom, Richard Watson, Aaron Baker, Serena Ayers, and David L. Anderson 39

Dispersing Vulture Roosts on Communication Towers. Michael l. Avery, John s,

Humphrey, Eric A. Tillman, Kimberly O. Phares, and Jane E. Hatcher 45

Raptor Abundance and Habitat Use in a Highly-Disturbed-Forest Landscape in

Western Uganda. Nathaniel E. Seavy and Christine K. Apodaca 51

Trophic Niche of North American Great Horned Owix. Lee a. Cromrich, Denver w.

Holt, and Shawne M. Leasure 58


Social Organization of a Trio Of Bearded Vultures ( Gypaetus barbatus) : Sexual and Parental

Roles. Joan Bertran and Antoni Margalida 66

Genetic Evidence of Ali.oparental Care of a Female Lesser Kestrei. in an Alien Nest. Pedro J.

Cordero, Jose M. Aparicio, and David T. Parkin 70

NE.STING OF Long-eared Owls Along the Lower Big Lost River, Idaho: A Comparison of 1975-76

and 1996-97. Natalie A. Fahler and Lester D. Flake 73

Behavioral and Ph\sical Development of a Nestling Crested Eagle {Morphnus GuiANENsrs)

.

David

F. Whitacre, Juventino Lopez Avila, and Gregorio Lopez Avila 77

Spring Weather and Breeding Success of the Eurasian Kestrel {Falco riNNUNCULUs) in Urban

Rome, Italy. Luca Salvati 81

Eatal Caryospora Infection in a Free-living Juvenile Eurasian Kestrel {Falco riNmmcuLus) .Olivei:

Krone 84

Book Review. Edited by Jeffrey S. Marks 87

Manuscript Referees 89

Number 2

An Urban Osprey Population Established by Translocation. Mark s. Marteii, Judy

Voigt Englund, and Harrison B. Tordoff 91

Breeding Grounds, Winter Ranges, and Migratory Routes of Raptors in the

Mountain West. Stephen W. Hoffman, Jeff P. Smith, and Timothy D. Meehan 97

Circuitous Autumn Migration in the Short-toed Eagle( Circaetus gallicus) .

Nicolantonio Agostini, Luca Baghino, Charles Coleiro, Ferdinando Corbi, and Guido Premuda Ill

Spring Migration of Adult and Immature Buzzards {Buteo buteo) through Elat,

Israel: Timing and Body Size. Reuven Yosef, Piotr Tryjanowski, and Keith L. Bildstein 115

Provisioning Rates and Time Budgets of Adult and Nestling Bald Eagles

AT Inland Wisconsin Nests. D. Keith Wamke, David E. Andersen, Cheryl R. Dykstra,

Michael W. Meyer, and William H. Karasov 121

A Line Transect Survey of Wintering Raptors in the Western Po Plain of

Northern Italy. Giovanni Boano and Roberto Toffoli 128


Bald Eagle Reproductive Performance Following Video Camera Placement. Cheryl R. Dykstra,

Michael W. Meyer, and D. Keith Warnke 136

Absence of Bi.ood Parasites in Nestlings of the Eleonora’s Falcon {Falco ejmonoraf). Alejandro

Martinez-Abram and Gerardo Urios 139

Possible Choking Mortalities of Adult Northern Goshawks. Thomas D. Bloxton, Andi Rogers,

Michael F. Ingraldi, Steve Rosenstock, John M. Marzluff, and Sean P. Finn 141

Exhumation of Food by Turkey Vulture. Harvey R. Smith, Richard M. DeGraaf, and Richard S.

Miller 144

Bats as Prey of Barn Owls ( lYro alba) in a Tropical Savanna in Bolivia. Julieta Vargas, Carlos

Landaeta A., and Javier A. Simonetti 146

Food of the Lesser Kestrel (Falco naumanni) in its Winter Quarters in South Africa. Grzegorz

Kopij 148

Red-shouldered Hawk Feeds on Carrion. Bill Pranty 152

Letters

First Repiacement Clutch by a Polvandrous Trio of Bearded Vultures (Gypaetus baebatus) in the

Spanish Pyrenees. Antoni Margalida and Joan Bertran 154

Mississippi Kites Use Swallow-tailed Kite Nests. Jennifer O. Coulson 155

Erratum 157

Number 3

Population Status of Breeding Bald Eagles in Washington at the end of the

20th Century. James W. Watson, Derek Stinson, Kelly R. McAllister, and Thomas E. Owens 161

Response Distance of Ferruginous Pygmy-Owls to Broadcasted Conspecific

Calls. Glenn a. Proudfoot, Sam L. Beasom, Felipe Chavez-Ramirez, and Jody L. Mays 170

POST-FLEDGING SURVIVAL AND DISPERSAL OF PEREGRINE FALCONS DURING A RESTORATION

Project. LarkinA. Powell, DanJ. Calvert, Irene M. Barry, and Lowell Washburn 176

Morphology, Genetics, and the Value of Voucher Specimens: An Example with

CATT/ARTES Vultures. Carole S. Griffiths andJohn M. Bates 183

Oral Administration of Tiletamine/Zolazepam for the Immobilization of the

Common Buzzard {BUTEO BUTEO) . Martinjanovsky, Thomas Ruf, and Wolfgang Zenker 188

Hunting Behavior of and Space Use by Eastern Screech-Owls during the

Breeding Season. Jennifer E. Buhay and Gary Ritchison 194


ScHizocHROMiSM IN A PEREGRINE Falcon erom ARIZONA. David H. Ellis, Lynn W. Oliphant, and James

K. Fackler 200

Natal Dispersal of the Crested Caracara (Caracara cherjway) in Florida. Nicole M. Nemeth and

Joan L. Morrison 203

Recent Records of Crowned Eagles {Harpyhaliaetus coronatus) from Argentina, 1981-2000.

M. Isabel Bellocq, Patricio Ramirez-Llorens, and Julieta Filloy 206

New Observations of the Peregrine Falcon {Falco peregrinus) in Peru. Marc Kery 213

DNA Polymorphisms in Boreai. Owls {Aegolius funereus) . Janne Beheim, Katrine Eldegard, Gro

Bj0rnstad, Mats Isaksson, Geir Sonerud, Olav Heie, and Helge Klungland 218

Post-fledging Movements and Foraging Habitats of Immature White-tailed Sea Eagi.es in the

Nemuro Region, Hokkaido, Japan. Saiko Shiraki 220

Habitat Preferences, Breeding Success, and Diet of the Barn Owl (Tyto alba) in Rome; Urban

versus Rural Territories. Luca Salvati, Lamberto Ranazzi, and Alberto Manganaro 224

Incidence of Naturally-healed Fractures in the Pectoral Bones of North American Accipiters.

Aaron J. Roth, Gwilym S. Jones, and Thomas W. French 229

Piasma Chemistry Reference Values in Free-living Bonelli’s Fagle (Hieraaetus fasciatus)

Nestlings. Javier Balbontin and Miguel Ferrer 231

Letters

The Fox Kestrel {Falco alopex) Hoytrs. Tiziano Londei 236

Probable Breeding of Short-eared Owls in Southern West Virginia. Frank K. Ammer and Petra

Bohall Wood 237

Endangered Egyptian Vulture {Neophron percnopierus) Entangled in Powerline Ground-wire Stabilizer.

Laura Gangoso and Cesar J. Palacios 238

Barred Forest-Falcon {Miciustur ruficollis) Predation on a Hummingbird. Tony Nunnery and

Mark R. Welford 239

Book Reviews. Edited byjeffrey S. Marks 241

Number 4

Foraging Ecology of Nesting Bald Eagles in Arizona, w. Grainger Hunt, Ronald e.

Jackman, Daniel E. Driscoll, and Edward W. Bianchi 245

Vernal Migration of Bai.d Eagles from a Southern Colorado Wintering Area.

Alan R. Harmata 256

Does Northern Goshawk Breeding Occupancy Vary with Nest-stand Character-

istics on the Olympic PeNINSUIA, Washington? Sean P. Finn, Daniel E. Varland, and

John M. Marzluff 265

Subordinate Males Sire Offspring in Madagascar Fish-Eagle {Haliaeetus vociee-

ROWES) POLYVNDROUS BREEDING GROUPS. Ruth E. Tingay, Melanie Culver, Eric M.

Hallerman, James D. Fraser, and Richard T. Watson 280

Nesting and Perching Habitat Use of the Madagascar Fish-Eagle. James Berkeiman,

James D. Fraser, and Richard T. Watson 287

Use of Vegetative Structure by Powerful Owls in Outer Urban Melbourne,

Victoria, Austraija—Implications for Management. Rayiene Cooke, Robert WaiUs,

andJohn White 294

Nest-Site Selection of the Crowned Hawk-Eagle in the Eorests of Kwazulu-

NATAL, South Africa, and TAI, Ivory Coast. Gerard Malan and Susanne Shultz 300


Juvenile Dispersal of Madagascar Fish-Eagles Tracked by Satellite Telemetry. Simon

Rafanomezantsoa, Richard T. Watson, and Russell Thorstrom 309

Prey OF the Peregrine Falcon {Falco Peregrinus cassini) in Southern Argentina and Chile. David

H. Ellis, Beth Ann Sabo, James K. Fackler, and Brian A. Millsap 315

An Elevated Net Assembly to Capture Nesting Raptors. Eugene A. Jacobs and Glenn A. Proudfoot 320

Florida Bald Eagle {Haliaeetus teucocephalus) Egg Characteristics. M. Alan Jenkins, Steve K.

Sherrod, David A. Wiedenfeld, and Donald H. Wolfe, Jr. 324

Osprey Ecology IN THE Mangroves OF Southeastern Brazil. Robson Silva e Silva, Fabio Olmos .... 328

Diet of Breeding Tropical Screech-Owls ( Otus choliba) in Southeastern Brazil. Jose Carlos

Motta-Junior 332

Letters

Comments of the First Nesting Record of the Nest of a Slaty-backed Forest Falcon {Micrastur

MIRANDOLLEI) IN THE ECUADORIAN AMAZON. Russell Thorstrom 335

Micrastur or Accipiter, That is the Question. Tjitte de Vries and Cristian Melo

Book Reviews. Edited by Jeffery S. Marks

Information For Contributors

337

338

340

Index to Volume 36 344

A Telemetry Receiver Designed with

The Researcher in MindWhat you've been waiting fori

fui.illv, ,1 h.Kjhly th.ifine! telemetry receiver th.it wrtqhs less than 13 ounces, is

(ompleteiy user proqr.imm.ible <ind offers v.uuble scan r.ites over .ill frequencies For each animal bfinq

fr.uked, ttie larqe KD rJ'Spl.iy provides not only the frequeiuy (to lOOH.’) and channel number, but also a

; character alphanumenr comment field and a digital signal strength meter. Stop carrying receivers that are

the si.’t* of a lunch bo» or cost over SlSOO. The features and performance of the new R-1000 pocket si/ed

tolem.'trv ffcoivor Aill impress you. and the prue will convince yOu.

Other Featurti Include:

• F.irtory tuned to any -.MM/ wide seqment in the 148 174MH/ Band • Very liiqh sensitivity of 148dBm to

I'jOdBm • Illuminated display and Veyp.id for use ui low bqht or darkness • User selectable scan rates

from 1 30 seconds in 1 second steps • Rechargeable battenes operate tfie receiver for 12 hours and

can be replaced with standard AA Alkaline batteries in the field.

Both 12vdc and llOvac chargers are included.

• 6. r ( 15.bcm) higti.

2.6" (6.6cm) wide,

1.5" (3.8cm) deep

• 3 year warranty

• 1 day delisrery

$695.00Please specify' desired 4MM/

wide segment m the

148 174MHr band

Visit our

website for

complete

spec ihc ations,

operating

manual and

infijirn.it'C'n

i.n the R 1000' 'I . .i!! oij'

t .' I ! f r I ‘ (

*1) 111. lei

rei elver r;,i

Try the

New R-1000and You'll BtImpressed!

COMMUNICATIONS SPECIALISTS. INC

Buteo3130 Laurel RoadShipman, VA 22971

Books800-722-2460 [email protected] www.buteobooks.com

BUTEO BOOKS is the largest retailer ofOrnithology titles in

North America, with over 2000 in-print titles in stock.

In-Print Falconry and Birds of Prev

Handbook of the Birds of the World. The first seven volumes of this projected sixteen-

volume work have been published, including Volume 2, covering the diurnal raptors, and

Volume 3, covering owls. They are priced at $185 each.

The Raptor Almanac: A Comprehensive Guide to Eagles, Hawks, Falcons, and Vultures.

Scott Weidensaul. Lyons Press, 2000. 382 pp. Color photos. Cloth. $40.00

The Harris Hawk: Management, Training and Hunting. Lee W. Harris. Swan Hill Press,

2001. 144 pp. Color and b&w photos and illustrations. Cloth. $32.95

Rare and Out-of-print Falconry

Usually available from Buteo Books, the classic reference on diurnal raptors: Brown &Amadon: Eagles, Hawks and Falcons ofthe World. First English edition, 1968. $300.

Birds of North America series

individual species accountsfor

Swallow-tailed Kite

White-tailed Kite

Snail Kite

Mississippi Kite

Bald Eagle

Northern Harrier

Sharp-shinned HawkCooper’s HawkNorthern Goshawk

Common Black-Hawk

Harris’ HawkRed-shouldered HawkBroad-winged HawkSwainson’s HawkWhite-tailed Hawk

over 500 species, including:

Zone-tailed HawkHawaiian HawkRed-tailed HawkFerruginous HawkCrested Caracara

American Kestrel

Merlin

Gyrfalcon

Prairie Falcon

Bam OwlFlammulated OwlEastern Screech-Owl

Whiskered Screech-Owl

Great Homed Owl

Snowy Owl

Northern Hawk OwlNorthern Pygmy-Owl.

Ferruginous Pygmy-Owl

Elf OwlBurrowing OwlSpotted OwlBarred OwlGreat Gray OwlLong-eared OwlShort-eared Owl (R)

Boreal OwlNorthern Saw-whet OwlAvailable soon:

American Kestrel

California Condor

2003 ANNUAL MEETING

The Raptor Research Foundation, Inc. 2003 annual meeting will be held on 3-7 September 2003in Anchorage, Alaska. For information about the meeting see the following website: http://www.alaskabird.org or contact Nancy DeWitt ([email protected])

.

Persons interested in predatory birds are invited to join The Raptor Research Foundation, Inc. Sendinquests for information concerning membership, subscriptions, special publications, or change of address

to OSNA, P.O. Box 1897, Lawrence, KS 66044-8897, U.S.A.

TheJournal ofRaptor Research (ISSN 0892-1016) is published quarterly and available to individuals for $33.00per year and to libraries and institutions for $50.00 per year from The Raptor Research Foundation, Inc., 14377117th Street South, Hastings, Minnesota 55033, U.S.A. (Add $3 for destinations outside of the continental UnitedStates.) Periodicals postage paid at Hastings, Minnesota, and additional mailing offices. POSTMASTER: Sendaddress changes to TheJournal ofRaptor Research, OSNA, P.O. Box 1897, Lawrence, KS 66044-8897, U.S.A.

Printed by Allen Press, Inc., Lawrence, Kansas, U.S.A.

Copyright 2002 by The Raptor Research Foundation, Inc. Printed in U.S.A.

© This paper meets the requirements of ANSi/NISO Z39.48-1992 (Permanence of Paper).

Raptor Research Foundation, Inc., Awards

Lifetime Achievement Awards

The Tom Cade Award recognizes an individual who has made significant advances in the area of captive prop-

agation and reintroduction of raptors. Nomination packets can be submitted at any time. Contact: Brian

Walton, Predatory Bird Research Group, Long Marine Laboratory, University of California, Santa Cruz, CA95064 U.S.A.; tel. 408-459-2466; e-mail: [email protected].

The Fran and Frederick Hamerstrom Award recognizes an individual who has contributed significandy to the

understanding of raptor ecology and natural history. Nomination packets can be submitted at any time. Con-

tact: Dr. Clint Bo<il, Texas Cooperative Fish and Wildlife Research Unit, BRD/USGS, Texas Tech University,

15th Street & Boston, Ag Science Bldg., Room 218, Lubbock TX 79409-2120 U.S.A.; tel. (806) 742-2851;

e-mail: [email protected].

Student Recognition and Travel Assistance Awards

The James R. Koplin Travel Award is given to a student who is the senior author and presenter of a paper or

poster to be presented at the RRF annual meeting for which travel funds are requested. Contact; Dr. Patricia

A. Hall, 5937 E. Abbey Rd. Flagstaff, AZ 86004 U.S.A.; tel. 520-526-6222; e-mail: [email protected].

Application Deadline: due date for meeting abstract.

The William C. Andersen Memorial Award is given to the students who are senior authors and presenters of the

best student oral and poster presentation at the annual RRF meeting. Contact: Laurie Goodrich, HawkMountain Sanctuary, 1700 Hawk Mountain Road, Kempton, PA 19529 U.S.A.; tel. 610-756-6961; email;

[email protected]. Application Deadline: due date for meeting abstract; no special application

is needed.

Grants

For each of the following grants, complete applications must be submitted to the contact person indicated by

15 February. Recipients will be notified by 15 April.

The Dean Amadon Grant for $200-400 is designed to assist persons working in the area of distribution and sys-

tematics (taxonomy) of raptors. Contact: Dr. Carole Griffiths, 251 Martling Ave., Tarrytown, NY 10591

U.S.A.; tel. 914-631-2911; e-mail: [email protected].

The Stephen R. Tully Memorial Grant for $500 is given to support research, management, and conservation of

raptors, especially to students and amateurs with limited access to alternative funding. Contact; Dr. KimTitus, Alaska Department of Fish and Game, Division of Wildlife Conservation, P.O. Box 240020, Douglas,

AK 99824 U.S.A; e-mail; [email protected].

The Leslie Brown Memorial Grant for up to $1,000 to support research and/or dissemination of information

on birds of prey, especially to proposals concerning African raptors. Contact: Dr. Jeffrey L. Lincer, 9251

Golondrina Dr., La Mesa, CA 91941 U.S.A.; e-mail: [email protected].

The journal of raptor research - Internet...

Documents

Transcript of The journal of raptor research - Internet...