) AND BOREAL CHORUS FROGS ( PSEUDACRIS MACULATA R ...

AN ASSESSMENT OF SURVEY METHODOLOGY, CALLING ACTIVITY, AND

HABITAT ASSOCIATIONS OF WOOD FROGS (RANA SYLVATICA) AND BOREAL

CHORUS FROGS (PSEUDACRIS MACULATA) IN A TUNDRA BIOME

R. Nicholas Mannan, B.S.

A Thesis

In

WILDLIFE SCIENCE

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCE

Gad Perry Chair

David E. Andersen

Co Chair

Clint W. Boal Co Chair

Fred Hartmeister Dean of the Graduate School

May, 2008

Texas Tech University, Robert N. Mannan, May, 2008

ii

ACKNOWLEDGEMENTS

All work was conducted under ACUC permit number 06021-05 and Parks Canada

research permit number Wap-2005-518. I thank Parks Canada, Wapusk National Park;

Texas Tech University Department of Natural Resources Management; the U.S.

Geological Survey, Texas Cooperative Fish and Wildlife Research Unit; and the U.S.

Geological Survey, Minnesota Cooperative Fish and Wildlife Research Unit for

providing funding and logistical support. The Eastern Prairie Population Canada Goose

Committee of the Technical Section of the Mississippi Flyway Council provided

logistical support for this project through the Nestor One field research camp, and M.

Gillespie (Manitoba Conservation) coordinated camp support. M. Reiter, C. Henneman,

G. Lundie, W. Souer, B. Olson, M. Jones, S. Maxson, B. Luebke, M. Miller, B. Nack, T.

Bishop, J. Huener, J. Lawrence, B. McCardle, and M. Roell assisted with data collection.

Gad Perry, David E. Andersen, and Clint W. Boal provided guidance and demonstrated

unending patience. David B. Wester provided integral statistical support. Finally, I thank

my family and office mates for their support in all matters.


iii

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

LIST OF TABLES v

LIST OF FIGURES vii

CHAPTER

I. OVERVIEW 1

II. AN ASSESSMENT OF ANURAN SURVEY METHODOLOGY IN A

TUNDRA BIOME 5

Abstract 5

Introduction 6

Study Area 8

Methods 9

Results 14

Discussion 16

III. FACTORS AFFECTING CALLING ACTIVITY OF BOREAL CHORUS

FROGS (PSEUDACRIS MACULATA) AND WOOD FROGS (RANA

SYLVATICA) NEAR CAPE CHURCHILL, MANITOBA 28

Abstract 28

Introduction 29

Study Area 30

Methods 31


iv

Results 33

Discussion 34

IV. HABITAT ASSOCIATIONS OF BOREAL CHORUS FROGS (PSEUDACRIS

MACULATA) AND WOOD FROGS (RANA SYLVATICA) IN A TUNDRA

BIOME 43

Abstract 43

Introduction 44

Study Area 46

Methods 47

Results 53

Discussion 55

LITERATURE CITED 72

APENDIX A 77

AUTOMATED RECORDER COMPONENTS 77


v

LIST OF TABLES

3.1 Results of a regression analysis of a linear mixed effects model

used to model wood frog call activity, near Cape Churchill,

Manitoba, Canada, 2007. 41

3.2 Results of a regression analysis of a linear mixed effects

model used to model boreal chorus frog call activity, near Cape

Churchill, Manitoba, Canada, 2007. 42

4.1 Mean values of habitat variables at detection and non-detection

sites for wood frogs and boreal chorus frogs near Cape

Churchill, Manitoba, 2006-2007. 60

4.2 Mean values of percent cover, vegetation height, tallest piece

of vegetation, pH, and TDS of triangulation locations and

corresponding breeding sites near Cape Churchill, Manitoba,

2006-2007. 61

4.3 Number of sites with and without anuran detections that

contained evidence of goose herbivory near Cape Churchill,

Manitoba, 2006-2007. 62


vi

4.4 Correlation coefficients and P-values (in parentheses) of

measured habitat variables at potential breeding sites of

boreal chorus frogs and wood frogs near Cape Churchill,

Manitoba 2006-2007 (n = 204). 63

4.5 Eigenvalues of a correlation matrix and the % variation of

habitat variables explained in models of habitat associated

with anuran locations near Cape Churchill, Manitoba,

2006-2007. 64

4.6 Results of a post-hoc MANOVA test for within-model

significance when predicting anuran presence near Cape

Churchill, Manitoba, 2006-2007 (n = 202). 65

4.7 Loading scores of the variables within components of

habitat models describing anuran locations near Cape Churchill,

Manitoba, 2006-2007. 68


vii

LIST OF FIGURES

2.1 Study plots near Cape Churchill, Manitoba, where anuran

surveys were conducted in 2006 and 2007. 22

2.2 The change in the numbers of Rana sylvatica detected

before and after broadcasting advertisement calls near

Cape Churchill, Manitoba, 2006-2007. 23

2.3 The change in the number of Pseudacris maculata detected

before and after broadcasting advertisement calls near


2.4 Difference in the number of Rana sylvatica detections made

by observers and using automated recorders near Cape


2.5 The discrepancy between Pseudacris maculata detections

made by observers and using automated recorders near Cape



viii

2.6 The percentage of broadcasts detected by automated recorders

conducted at 20 m increments along transects beginning at

automated recorders and traveling at bearings of 0, 90, 180

and 270 degrees, near Cape Churchill, Manitoba, 2006-2007. 27

3.1 Study plots near Cape Churchill, Manitoba, where anuran

surveys were conducted in 2007. 38

3.2 Mean and standard deviation of the number of anurans

detected as a function of (A) date, (B) time of day,

(C) temperature, and (D) relative humidity near Cape

Churchill, Manitoba, Canada, 2007 (□ = Wood frogs,

▲=Boreal chorus frogs). 39

4.1 Study plots near Cape Churchill, Manitoba, where

anuran surveys were conducted in 2006 and 2007. 59

4.2 The negative relationship between component one and

wood frog presence, depicted by a logistic regression line

near Cape Churchill, Manitoba, 2006-2007. 66


ix

4.3 The negative relationship between component one and

wood frog presence, depicted by a logistic regression line

near Cape Churchill, Manitoba, 2006-2007. 67

4.4 Means and 95% confidence intervals of (A) average

vegetation height, (B) % cover by sedge and willow,

(C) average height of tallest vegetation, (D) TDS, and

(E) pH, with respect to evidence of goose herbivory near


5.1 Diagram of automated recorder components near


5.2 Photograph of automated recorder components near


5.3 Control board for automated recorder near Cape Churchill,

Manitoba, 2006-2007. 80


1

CHAPTER I

OVERVIEW

Two species of anurans, the boreal chorus frog (Pseudacris maculata) and

wood frog (Rana sylvatica), inhabit the tundra biome near Cape Churchill, Manitoba, and

potentially are susceptible to changes in vegetative structure and composition, caused

primarily by foraging geese and changes in climate. Both species of frogs have extensive

distributions. The wood frog inhabits areas within much of Canada and Alaska, but also

exists along the northeastern seaboard of the United States, through the Great Lakes

region and into the northern Midwest states (Stebbins 1951, USGS 2002). The boreal

chorus frog is the northernmost of the chorus frogs with a range extending from areas in

Arizona and New Mexico through the Midwest, north into Alberta, Ontario,

Saskatchewan, Manitoba, and parts of the Northwest Territories (Koch and Peterson

1995, USGS 2002).

Both species are common within their ranges and much is known about their life

histories (e.g., see Heatwole 1961, Berven 1990). However, both wood frogs and boreal

chorus frogs show considerable morphological and behavioral variation across their

respective ranges (Pettus and Spencer 1964, Berven 1990), and this variation may

influence the way they react to changes in climatic and other environmental

perturbations. For example, in contrast to other areas in which boreal chorus frogs and

wood frogs are found, there are few plants that provide cover or grow very tall in the


2

tundra biome in northern Manitoba. Sedges (Carex aquatilis, C. rupestris, and C.

glacialis) and small willows (Salix planifolia, S. herbacea and S. brachycarp) are the

only plants that may provide the shelter and structure important to reproduction in frogs.

Thus, factors that affect tundra vegetation likely affect anurans inhabiting this region.

Two of the factors most likely to affect tundra vegetation along the west coast of the

Hudson Bay are changing climate and increased herbivory by geese.

Along the west coast of Hudson Bay, geese feed heavily on sedges. Over the past

two decades, mid-continent light geese [snow geese (Chen caerulescens) and Ross’s

geese (Chen rossii)] populations have increased at an annual rate of 5-7% (Batt 1997,

Jefferies and Rockwell 2002). Increased grazing has altered vegetation production as well

as the overall vegetative composition in some areas (Cargill and Jefferies 1989, Jefferies

and Rockwell 2002). Removal of sedges by foraging geese may impact anurans by

altering wetland structure and water quality. Reduction of sedges may remove the

necessary cover and tall vegetative structure integral for anurans to complete their life

cycle. Also, the removal of sedges may lower pH of the water at potential breeding sites,

a hydrological characteristic important to the survival of both wood frogs and chorus

frogs (Corn et al. 1989, Wikberg and Mucina 2002). Currently, the effects of goose

herbivory on anuran-habitat associations are unknown.

To assess anuran population status and monitor changes in anuran populations

inhabiting the tundra, efficient survey methodology is necessary. Established survey

methods for anurans include road-side surveys, listening stations, repeated surveys at

selected breeding areas, and counts of egg masses (Shirose et al. 1997, Crouch and Paton


3

2000, USGS 2001, Weir et al. 2005). However, because most tundra landscapes are

relatively isolated and experience extreme climatic conditions, many standard anuran

survey methods are not be feasible or effective there. Both the relatively short time period

during which surveys can be conducted and the difficulty in reaching and supporting field

operations are two factors that complicate surveying anurans in the tundra.

Survey efforts in tundra ecosystems might be made more efficient in several

ways. The first is to increase the detectability of anuran species. Males of some anuran

species increase calling frequency after broadcasts of conspecific advertisement calls

(Wells and Greer 1981, Sullivan 1985). A positive response to broadcasted conspecific

advertisement calls could increase the efficiency of surveys, thus decreasing the number

of surveys necessary to accurately assess presence or absence. No information exists

regarding how wood frogs or boreal chorus frogs respond to broadcasted advertisement

calls.

Another possible approach to increase the effectiveness of anuran surveys is to

maximize the area surveyed. There are few roads in most subarctic and arctic tundra

landscapes, rendering roadside counts impractical. However, automated audio recorders

(hereafter automated recorders) have been used at anuran breeding locations to record

call activity (Penman et al. 2005); it may be possible to use a series of automated

recorders, placed at potential anuran breeding locations, to detect anuran presence and

effectively survey large areas.

Finally, high-latitude tundra landscapes experience extensive daylight during

short summers, providing a brief annual period for anurans to breed. Environmental


4

variables such as light intensity have been suggested to affect the calling patterns of

anurans (Oseen and Wassersug 2002). Effective survey protocols should take advantage

of peak periods of calling, but currently it is unclear how weather and time of day affect

calling activity of anurans in the subartic and arctic tundra (e.g., see Andersen et al.

2005).

The following chapters address the issues discussed above. In Chapter I, I

evaluate the possibility of soliciting calls from non-calling anurans by manually

broadcasting conspecific advertisement calls as well as the use of automated recorders to

increase survey coverage. In Chapter II, I describe factors affecting the calling patterns of

anurans in a tundra biome. Finally, in Chapter III, I examine habitat selection and

associations of tundra-dwelling anurans with regard to vegetation, water quality, and

patches of vegetation affected by goose herbivory.

Throughout this thesis terminology remains consistent, but is redefined in each

chapter because each chapter is structured to stand alone as an independent manuscript.

This allows readers to understand individual chapters without reading the whole thesis.

All references are presented in a single section at the end of the manuscript.


5

CHAPTER II

AN ASSESSMENT OF ANURAN SURVEY METHODOLOGY IN A TUNDRA

BIOME

Abstract

The tundra biome near Cape Churchill, Manitoba is being influenced by global

climate change and herbivory from an increasing population of light geese. These

environmental changes may impact anuran populations, although little is known about

population trends in anurans in the region. The isolation of the region may render

traditional anuran survey methods ineffective. I tested two methods of surveying for two

anuran species, boreal chorus frogs (Pseudacris maculata) and wood frogs (Rana

sylvatica). I solicited calls from non-calling anurans by manually broadcasting

conspecific advertisement calls, and I used automated audio recorders to increase survey

coverage. I detected 0.38 additional wood frogs per survey when broadcast calls were

employed, compared to surveys without broadcasts. I was unable to detect additional

boreal chorus frogs by broadcasting conspecific advertisement calls. Using automated

audio recorders, I was able to identify anuran presence in a radius of 100 m, but

detections of wood frogs were low compared to manual surveys. I suggest that broadcasts

of wood frog advertisement calls be implemented into surveys for wood frogs in the

tundra biome, and that additional research is necessary to determine whether solicitation

can be used to increase detection of other anuran species.


6

Introduction

Surveys are integral to wildlife science and are applied in both research and

management in a variety of systems. Because of their wide applications, survey protocols

must be appropriate for the system under investigation. Design of survey protocols

should incorporate considerations of detection efficiencies as well as other abiotic and

biotic constraints within a particular region. Survey protocols should also be: (1)

consistent through time; (2) effective; (3) efficient; and if possible (4) comparable to

other surveys conducted in the same area or of the same species. Because of the diversity

of the applications and conditions under which surveys are conducted, survey protocols

are ideally regionally and species-specific.

The design of an ideal survey protocol is complicated. Often, particular protocol

attributes represent a trade-off between information quality and quantity. For example,

increasing survey intensity will likely yield a more accurate estimate of the abundance of

the species under investigation, but will also increase the time or funds needed to conduct

the survey. Ultimately, increasing survey intensity usually leads to a decrease in the total

area surveyed. Limitations of particular survey protocols create a demand for new or

improved protocols where the need for “trade offs” is minimized.

Increasing species detection probability is one approach to reducing the trade off

between quality and quantity. An increase in detection probability reduces the number of

survey repetitions needed to yield accurate estimates of species numbers (MacKenzie et

al. 2002). One approach to increasing detection probability of cryptic species is inducing

a response from the animals being surveyed. Biologists often broadcast avian calls to


7

solicit conspecific calls from individuals that would have otherwise gone undetected

(e.g., see Conway and Simon 2003).

Another approach to reducing the trade-off between quality and quantity is

increasing the efficiency of the surveyor. Automated audio recorders (hereafter

automated recorders) may be used to detect any vocal species allowing a single person to

collect data across a large area. Also, automated recorders have a good chance of

detecting cryptic vocal species that call intermittently, thereby reducing the need for

multiple surveys. Audio recorders have been placed at anuran breeding locations to

record call activity (e.g., see Penman et al. 2005). However, the use of automated

recorders as a surveying method is relatively new and is still being developed.

Recent work has identified two species of anurans, the boreal chorus frog

(Pseudacris maculata) and wood frog (Rana sylvatica), inhabiting the tundra biome near

the coast of the Hudson Bay in Manitoba (e.g., see Boal and Andersen 2003, Andersen et

al. 2005, Reiter et al. in review). Both species occupy the tundra across a gradient from

coastal tundra through interior sedge meadow/wetland to the tundra-boreal forest

interface. The subarctic tundra in northern Manitoba is covered in snow for most of the

year. However, for four months during the summer, the tundra becomes a marsh

providing nesting grounds for many bird species as well as breeding habitat for the boreal

chorus frog and the wood frog (Boal and Andersen 2003, Parks Canada 2007).

The tundra offers a unique set of challenges for anuran surveys rendering most

traditional methods inappropriate. Traditional survey methods for anurans include road-

side surveys, listening stations, repeated surveys at selected breeding areas, and counts of


8

egg masses (Heyer et al. 1994, Crouch and Paton 2000). Much of the tundra in North

America is roadless and summer travel is limited to helicopters or distances that can be

walked (Parks Canada 2007). This renders roadside surveys impossible and repeated

visits to listing stations and egg mass counts, if conducted with helicopters, expensive or,

if walked, time intensive. Also, in Wapusk National Park where I conducted the study, a

local population of polar bears (Ursus maritimus) makes camping and nighttime surveys

unsafe and requires that all daytime work be conducted in pairs, doubling the expense of

survey efforts. Currently, no anuran survey protocol has been created for the tundra

biome.

In 2006 and 2007, I expanded upon previous work (Boal and Andersen 2003,

Andersen et al. 2005, Reiter et al. In review) and conducted anuran surveys in Wapusk

National Park near Cape Churchill, Manitoba to: (1) evaluate the response of boreal

chorus frogs and wood frogs to broadcasted conspecific advertisement calls; and (2)

compare the effectiveness of automated recorders and manual surveys for detecting

anuran presence in the subarctic tundra biome.

Study Area

Wapusk National Park is located on the southwest side of Hudson Bay, Manitoba,

Canada. The park boundary is 35 km southeast of the town of Churchill, and the park

covers approximately 11,475 km2. The study area is located inside the park in the

subarctic tundra biome, which encompassed a matrix of small upland ridges and lowland,

sedge-dominated marshes and included a mix of semi-permanent and permanent water


9

bodies throughout. Permafrost occurs near the surface, rendering most water bodies very

shallow. Winter temperatures are as low as -50 C with an average of -26 C and summer

temperatures range from -10 to 35 C with an average of 11 C (Parks Canada 2007). The

town of Churchill, located approximately 65 km northwest of Nestor One, the research

camp within the park, receives, on average, 436.1 mm of precipitation a year

(Environment Canada 2004). Most recreational uses are restricted in the park, except for

traditional uses such as hunting, trapping, fishing, and egg-collecting by local residents

and First Nations members.

I conducted field work primarily in the area surrounding Nestor One, a goose

research station located approximately two km from the Hudson Bay coastline south of

Cape Churchill (Easting: 0489270, Northing: 6502207; NAD 27). I collected data within

two 12.6 km2 study plots extending from near the coast of the Hudson Bay inland. The

study plots were situated 8 km apart and each had a diameter of 4 km (Fig. 1.1). All work

was conducted under the Texas Tech University Animal Care and Use Committee permit

number: 06021-05 and the Parks Canada research permit number: Wap-2005-518.

Methods

Surveys with broadcasted calls

In the summers of 2006 and 2007, I conducted anuran surveys at potential

breeding sites to evaluate the response of boreal chorus frogs and wood frogs to

broadcasted conspecific advertisement calls. To select potential breeding sites, I created

two 12.6 km2 circular study plots: a northern study plot established in 2006 and a


10

southern study plot established in 2007. These study plots were located approximately 4

km from Nestor One to avoid disturbance to goose nests under observation as part of

Canada goose (Branta canadensis interior) monitoring activities. Study plots began at the

coast of the Hudson Bay and had a diameter of 4 km that extended inland (Fig. 1.1). I

used ARCGIS [version 9.1] (ESRI, Redlands, Calif., USA; use of trade names does not

imply endorsement by the U.S. Geological Survey, the University of Minnesota, or Texas

Tech University) to randomly select 57 locations within the northern plot and 60

locations within the southern plot. Buffer zones ensured locations were not closer than

200 m from each other and the number of survey locations was dictated by the time and

logistical support available for survey activities. On the first visit to each random

location, I walked to the nearest potential anuran breeding site to establish locations for

surveys (described below). Because water bodies with depths ≤10 cm were likely to dry

up within two weeks, I defined potential anuran breeding sites as water bodies deeper

than 10 cm.

Between 30 May and 18 June 2006, I conducted three broadcast surveys

(described below) at each breeding site at ~ 6 day intervals. Between 31 May and 11 July

2007, I repeated surveys at 27 of the randomly selected potential breeding sites surveyed

in 2006 and conducted surveys at 60 additional potential breeding sites in my southern

study plot (Fig. 1.1). I surveyed the 27 potential anuran breeding sites in my northern

study area in both 2006 and 2007 to assess annual variation in habitat use by anurans, and

to account for potential changes in vegetation between years. Whether individual frogs

reuse the same breeding locations between years on my study site is not known. For the


11

purpose of this paper, in my analyses, I assumed that results obtained at the same survey

location (n = 27) were independent between years.

During each survey, I stood 5 m from the edge of the potential breeding site and

allowed one minute for anurans to acclimate to my presence. I then recorded the number

and species of anurans detected during a three-minute listening period. Following the

listening period, I conducted one of two treatments or a control. Treatments were

comprised of one minute of advertisement calls of either a boreal chorus frog or a wood

frog. The control was one minute with the absence of any broadcast (hereafter null

broadcasts). Following the treatment or control, I conducted another three-minute

listening period during which I recorded number and species of all anurans detected.

I used a random number generator to select which broadcast type would be used

in each survey. In 2006, I obtained recorded anuran calls from the U.S. Geological

Survey Amphibian Research and Monitoring Initiative [ARMI; USGS Upper Midwest

Environmental Science Center webpage (http://www.umesc.usgs.gov), last accessed 26

August 2006]. During 2007, I recorded and broadcasted calls from local anurans. I

broadcasted wood frog and boreal chorus frog advertisement calls with a megaphone

rotating in a circle and at an average of 67 (range = 64 – 71) and 78 (range = 71 – 80) dB,

respectively. I used sound levels slightly louder than naturally occurring advertisement

calls to ensure that broadcast stimuli reached all nearby anurans. All advertisement

broadcasts used during this study were comprised of two to three advertising males of

either wood frogs or boreal chorus frogs. Anurans sometimes call at the same time,

creating call overlap. Some anurans avoid this by calling sequentially (Fellers 1979,


12

Sullivan 1985, Swartz 1987). To minimize the likelihood that broadcasting overlapping

calls acted as a call deterrent, the broadcasts I used contained no call overlap.

To supplement the number of surveys at potential breeding sites occupied by

anurans, in 2007 I also systematically searched both study plots for presence of anurans. I

repeatedly walked (>2 times) eight transects located at 1-km intervals spanning study

plots. When I detected anurans, I walked to the breeding site from which the anurans

were calling and marked the location. I returned to 11 of these locations and conducted <

3 broadcast surveys in the same fashion described above.

Comparison between audile surveys and automated recorders

In 2006 and 2007, I placed 11 automated recorders at locations I thought likely to

contain anurans based on characteristics of vegetation and water body. Recorders were

separated from each other by > 200 m, and were programmed to record ambient sounds

for three minutes. I chose three minutes because most anuran species are detected within

the first 3 minutes of a survey (Shirose et al. 1997).

In 2007, after the end of the anuran calling season, I tested the capability of

automated recorders to detect broadcasted calls at different distances from four

directions. I broadcasted wood frog mating calls at 20 m increments from the recorder out

to 160 m along four transects. Transects began at the recorders and traveled away from

the recorders at bearings of 0, 90, 180 and 270 degrees. I then reviewed the recordings

and identified positive detections at increasing distances. All broadcasts were at an

average of 67 (range = 64 – 71) dB and conducted when wind speeds were below 10 km.


13

Statistical analysis

To compare the mean number of anurans of each species detected during the

three-minute listening period before and after broadcasts I conducted Wilcoxon matched-

pairs tests because my anuran count data were not normally distributed (Conover 1999). I

also conducted a Wilcoxon matched-pairs test to compare the mean number of anurans of

each species detected three minutes before and after null broadcasts. Finally, I conducted

a Mann-Whitney U test to compare the mean number of anurans detected during the

initial listing period of broadcast surveys and null broadcast surveys. Tests included data

only from sites where I knew anurans were present (based on previous detections of

calling anurans). I assumed for these tests that breeding sites were independent and frogs

did not move among sites between surveys, a common assumption in anuran surveys

(Heyer et al. 1994). I also treated surveys at the same site in different years as

independent. I only included the first survey of each treatment type from sites in the

analyses to avoid pseudoreplication. Anuran calls periodically overlapped, occasionally

making an accurate estimate of anuran numbers difficult. In such cases (n = 2), I recorded

a range of frogs present (e.g., 6-8). For analyses, I used the lowest number in each range

to reduce overestimation.

To compare the effectiveness of automated recorders and audile surveys for

detecting anuran presence, I conducted 25 simultaneous audile surveys at five sites

during a subset of the automated recorded surveys. My count data were not normally

distributed, therefore, I conducted Wilcoxon matched-pairs tests to compare the mean

number of anurans of each species detected by automated recorders and audile surveys. I


14

report means and standard deviations in the results. I made the assumption that each

recorder functioned with the same detection efficiency. This was not an unreasonable

assumption, as all recorders were assembled from the same parts at the same time.

Results


I conducted 432 broadcast surveys at 144 randomly selected sites, and 14 surveys

at 11 sites identified while walking transects over the course of the two field seasons. I

detected >1 anuran at 47 of the 155 sites surveyed. Broadcast types were randomly

selected and sometimes a broadcast type was repeated at a site. To avoid duplication of a

broadcast type from the same location, I used 99 of the 155 surveys conducted at sites

where anurans were present in my analysis. I conducted 41 broadcast surveys and 24 null

broadcast surveys at locations where wood frogs had previously been detected. I

conducted 18 broadcast surveys and 16 null broadcast surveys at locations where boreal

chorus frogs had previously been detected.

There was no difference in the number of wood frogs detected before (x= 0.541 ±

0.931) and after null broadcasts (x = 0.625 ± 1.13; z = 0.00, P > 0.999). Likewise, there

was not a significant difference in the number of boreal chorus frogs detected before (x =

1.06 ± 1.80) and after null broadcasts (x = 1.13 ± 1.74; z = 0.00, P > 0.999). Similarly,

there was no apparent difference in detections of boreal chorus frogs pre broadcast (x =

0.889 ± 1.37) and post broadcast (x = 1.00 ± 1.53; z = 0.00, P = 0.999; Fig. 1.3). In

contrast, wood frogs responded positively to the broadcasting of conspecific


15

advertisement calls. The mean number of wood frogs detected pre broadcast (x = 0.824 ±

1.38) increased (t = 12.00, z = 2.73, P = 0.006; Fig. 1.2) to 1.24 ± 1.51 post broadcast.

There was no difference in the number of wood frogs detected during the initial

listing period of broadcast surveys (x = 0.824 ± 1.38) and null broadcast surveys (x=

0.541 ±0.931; adjusted z = 0.938, P = 0.348). Similarly, there was no difference in the

number of boreal chorus frogs detected during the initial listing period of broadcast

surveys (x = 0.889 ± 1.37) and null broadcast surveys (x = 1.06 ± 1.80; adjusted z =

0.00, P > 0.999)


I conducted 25 audile surveys simultaneously with automated recorders over two

field seasons. Automated recorders (x = 0.600 ± 0.867) detected significantly fewer

wood frogs compared to audile surveys (x =0.960 ± 1.27, z = 2.20, P = 0.0277; Fig. 1.4).

In contrast, there was no difference between the number of chorus frogs detected with

automated recorders (x = 1.72 ± 1.31) compared to audile surveys (x = 1.44 ± 1.45; z =

3.30, P = 0.0009; Fig. 1.5).

I tested the capability of four automated recorders to detect broadcasts.

Automated recorders detected 100 percent of all broadcast up to 100 m (Fig 1.6). No

automated recorders detected broadcasts at 160 m (Fig 1.6).


16

Discussion

The subartic tundra is experiencing habitat changes due to a variety of factors, but

changes in plant communities resulting from herbivory by geese have recently received

considerable attention (Batt 1997, Jano et al. 1998). The mid-continent light goose (lesser

snow geese [Chen caerulescens] and Ross’s geese [Chen rossi]) population has increased

5-7% percent annually over the past 20 years and altered much of the vegetation in the

coastal and interior wetlands in the vicinity of Cape Churchill, Manitoba, Canada and

western and southern Hudson and James Bays (Batt 1997, Jefferies and Rockwell 2002).

Increased grazing has altered vegetation production and the overall vegetative

composition in some areas (Cargill and Jefferies 1984, Jefferies and Rockwell 2002). As

goose populations grow and the extent of vegetation change increases, it becomes

important to monitor local anuran populations and document potential influences of

habitat change. Increasing anuran detectability by soliciting calls from non calling

anurans and placing automated recorders at anuran breeding locations will aid in the

development of appropriate anuran survey methodology in the tundra biome.


Anuran calls are important in territoriality, species identification, mate location,

and mate choice (Wells 1977, Wells and Greer 1981, Gerhardt 1982, Ryan 1985,

Gerhardt et al. 2000). Call overlap is often avoided to maintain the integrity of

information transmitted through vocal broadcasts (Fellers 1979, Sullivan 1985, Swartz

1987) and many anuran species avoid calling simultaneously with nearby conspecifics to


17

reduce call overlap. Broadcasting conspecific advertisement calls has been documented

to increase call frequency in already calling anurans (Wells and Greer 1981, Benedix and

Narins 1999, Gerhardt et al. 2000), but until now, there has been no evidence that

broadcasting advertisement calls could increase the number of anurans detected in field

surveys.

In my study, using broadcasted advertisement calls slightly increased the number

of wood frogs detected per survey but did not effectively elicit calls from boreal chorus

frogs. Because of the importance of calls and the information within them, it is not

surprising that an audile stimulus simulating potential intra-specific competition resulted

in a response by one of the species I tested. Which attributes of broadcasted calls cued

responses is unknown, and boreal chorus frogs might also respond to a broadcast call if

call attributes, such as call volume, call frequency, or pitch, were different from the ones

I used.

Detecting a change in the number of calling anurans in a field experiment is

difficult, primarily because the size of the chorus under observation can affect the

precision at which abundances are estimated. In studies conducted in areas with high

densities of frogs and large choruses, numbers of calling anurans are sometimes

estimated as ranges. For example, the North American Amphibian Monitoring Program

(NAAMP) uses call index values (CIV) to estimate numbers of chorusing anurans in

three ranges: 1; single calling anuran, 2; multiple calling anurans with no call overlap, 3;

multiple calling anurans with call overlap. The number of anurans each CIV value

represents is species specific (e.g., wood frogs CIV 2 = 3-5 frogs). Representing numbers


18

of calling anurans in ranges renders rough estimates, which makes detections of small

changes in anuran numbers difficult. The density of anurans in the tundra landscape in

which I worked is low (Andersen et al. 2005), allowing me to estimate anuran numbers

without using ranges. Estimating anuran numbers, as opposed to ranges, likely

contributed to my ability to detect an increase of roughly 0.4 wood frogs per survey.

My results suggest that the decision of male wood frogs to call is affected by the

presence of intra-specific competition. The function of the anuran advertisement calls is

thought to be primarily mate attraction and location. Female anurans often choose mates

that call more often or with more volume (Ryan 1985). My call broadcasts simulated an

increase in local calling activity. Increased calling activity may serve as an indicator of

the presence of potential mates, and initiating calling in the presence of potential mates

would be advantageous. My results support previous work that suggested that part of the

decision of wood frogs to call is based in the perception of intra-specific competition

(Wells and Greer 1981, Burmeister et al. 1999).


The estimated number of calling wood frogs detected by automated recorders and

audile surveys differed. Automated recorders collapsed the three-dimensional aural world

into a single dimension, which may help explain the discrepancy between the numbers of

wood frogs detected by audile surveys and automated recorders. The ability to pinpoint

the source of calls likely contributed significantly to the ability of a human estimating the

number of calling anurans. Wood frogs make a series of single-note chirps resembling the


19

sound of boiling water, but with a higher pitch. During a chorus, wood frogs do not

always avoid call overlap. Without pinpointing wood frog locations, call overlap makes it

difficult to distinguish among individual frogs on a recording.

Although I did not detect a statistical difference in the number of detections made

during audile surveys and by automated recorders, more chorus frogs were detected by

automated recorders than were detected by observers during five of 25 simultaneous

surveys. Boreal chorus frogs usually call with no overlap, or in tandem pairs. In a chorus,

if one frog changes frequency others shift frequency to avoid call overlap (Schwartz

1987). Without pinpointing the source of calls it is difficult to distinguish between boreal

chorus frogs shifting frequency and new frogs joining the chorus. Shifts in frequency may

have acted as false positives, inflating the number of boreal chorus frogs I detected by

recorders.

Using automated recorders in my study did not result in accurate assessment of

the number of calling wood frogs, suggesting that use of automated recorders for

acquisition of specific count data of anurans must be done with caution. The automated

recorders did reliably detect anurans up to 100 m in any direction. Therefore, it may be

possible to use counts acquired from automated recorders as indices and derive and apply

species-specific correction factors to estimate counts. However, such a correction would

require knowledge or estimation of region- and species-specific bias in counts.

Automated recorders would also likely be effective in monitoring sites for

presence or absence, which could be used to monitor frog distribution. Also, because the

detection probability for anurans is likely <1, repeated visits to a site may be necessary to


20

accurately determine anuran presence or absence (e.g., see MacKenzie et al. 2002).

Automated recorders, if left active for an appropriate amount of time, would likely detect

all present anuran species. This would alleviate the need for observers to survey a site

multiple times.

Although automated recorders did not accurately assess exact numbers of calling

anurans it is possible to assess overall changes in numbers of anurans calling. This

information would be useful in assessing changes in calling activity across seasons and

over time as climate changes.

Management implications

Several studies have documented increased call frequency of anurans following

call broadcasts (Wells 1977, Wells and Greer 1981, Gerhardt 1982, Gerhardt et al. 2000).

My study demonstrates that it is possible to solicit a vocal response from non-calling

anurans of some species in the field. In situations where single-species surveys are to be

implemented, broadcasting conspecific mating calls may be a useful tool for increasing

detection levels, especially in areas containing low densities of anurans. In this study only

25% of the sites visited contained anurans. An increase in detection levels decreases the

necessary number of survey repetitions thereby decreasing the effort required to survey a

particular region with no loss to data quality. A decrease in required survey effort would

create more economical survey protocols and facilitate studies encompassing larger areas.

However, broadcasting should not be implemented in all anuran surveys. It is

likely that in large anuran choruses, where a small number of additional anurans calling


21

will not change estimates of abundance, broadcasting advertisement calls may prove

ineffective. Furthermore, it is unclear how broadcasting advertisement calls would affect

anuran calling patterns during surveys designed to gather information about an array of

species.

In this study, using automated recorders did not result in accurate assessment of

specific numbers of one species of calling anuran. Therefore, automated recorders in

subarctic tundra landscapes should be used for count data with caution, but are likely

suitable for documenting anuran presence. Automated recorders function without the

presence of an observer, which makes them especially useful for documenting anuran

presence or absence in isolated regions where repeated visits are logistically difficult.

While this study focused on the use of automated recorders for detecting anurans,

the use of automated recorders are not limited to anurans. For example, automated

recorders may be useful in avian studies. Avian and anuran surveys use similar methods,

such as point counts. Use of automated recorders in avian surveys would offer all the

same benefits and drawback that use of automated recorders in anuran surveys offer.


22

Figure 2.1. Study plots near Cape Churchill, Manitoba, where anuran surveys were

conducted in 2006 and 2007.


23

-4 -3 -2 -1 0 1 2 3 4

The numbers of R. sylvatica detected after broadcasting minus the number of R. sylvatica detected beforebroadcasting

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

Nu

mb

er o

f ob

serv

atio

ns

Figure 2.2. The change in the numbers of Rana sylvatica detected before and after

broadcasting advertisement calls near Cape Churchill, Manitoba, 2006-2007.


24

Figure 2.3. The change in the number of Pseudacris maculata detected before and after

broadcasting advertisement calls near Cape Churchill, Manitoba, 2006-2007.


25

-4 -3 -2 -1 0 1 2 3 4

Number of R. sylvatica detections made by the observer minus the number of R. sylvatica detectionsmade by the automated recorders

0

2

4

6

8

10

12

14

16

18

20

Nu

mb

er o

f ob

serv

atio

ns

Figure 2.4. Difference in the number of Rana sylvatica detections made by observers and

using automated recorders near Cape Churchill, Manitoba, 2006-2007.


26

-4 -3 -2 -1 0 1 2 3 4

Number of P. maculata detections made by the observer minus the number of P. maculata detectionsmade by the automated recorders

0

2

4

6

8

10

12

14

16

18

20

Nu

mb

er o

f ob

serv

atio

ns

Figure 2.5. The discrepancy of Pseudacris maculata detections made by observers and

using automated recorders near Cape Churchill, Manitoba, 2006-2007.


27

Figure 2.6. The percentage of broadcasts detected by automated recorders conducted at

20 m increments along transects beginning at automated recorders and traveling at

bearings of 0, 90, 180, and 270 degrees, near Cape Churchill, Manitoba, 2006-2007.


28

CHAPTER III

FACTORS AFFECTING CALLING ACTIVITY OF BOREAL CHORUS FROGS

(PSEUDACRIS MACULATA) AND WOOD FROGS (RANA SYLVATICA) NEAR

CAPE CHURCHILL, MANITOBA

Abstract

Little information exists regarding wood frogs (Rana sylvatica) and boreal chorus

frogs (Pseudacris maculata) in the tundra biome, where environmental conditions differ

from most of the rest of their breeding ranges. Understanding anuran calling patterns is

essential to most anuran survey methodology. During the summer of 2007, I placed

automated audio recorders at anuran breeding locations and recorded number of calling

anurans near Cape Churchill, Manitoba. I used data loggers and automated call recorders

to document date, time of day, temperature, and relative humidity. Automated recorders

detected wood frogs between 30 May and 2 July 2007, and boreal chorus frogs between

11 June and 5 July 2007. Calling activity of both wood frogs and boreal chorus frogs was

influenced by temperature and day of the year (DOY). Calling activity of boreal chorus

frogs was also influenced by time of day and relative humidity. Understanding calling

patterns with respect to weather patterns will facilitate future monitoring.


29

Introduction

Both boreal chorus frogs (Pseudacris maculata) and wood frogs (Rana sylvatica)

have extensive distributions across North America that extend into subarctic tundra in

northern Manitoba (USGS 2002, Stebbins 1951). Both species are common within their

ranges and much is known about their life histories (e.g., see Heatwole 1961, Berven

1990). However, little information exists regarding either of these species in the tundra

biome, where environmental conditions differ from most of the rest of their respective

breeding ranges (Boal and Andersen 2003, Andersen et al. 2005, Reiter et al. In review).

Tall trees, commonly associated with the breeding sites of both species, are lacking in the

tundra and northern latitudes have relatively short summers, long day lengths, and cold

temperatures, compared to other breeding habitats of wood frogs and boreal chorus frogs.

Both species of frogs show considerable morphological and behavioral variability across

their respective ranges and populations occurring in tundra biomes may differ

behaviorally in response to the extreme conditions present in the tundra (Pettus and

Spencer 1964, Berven 1990).

One behavior that may change in response to conditions in the tundra is calling

activity. In more temperate regions, both wood frogs and boreal chorus frogs are

considered explosive breeders (Oseen and Wassersug 2002, USGS 2002) because all

breeding takes place over a relatively short time interval. During this short breeding

season, environmental factors have little effect on calling activity. For example, in New

Brunswick, Canada, temperature and humidity had little effect on the calling activity of

wood frogs (Oseen and Wassersug 2002). However, temperature, humidity, and light


30

intensity affect calling patterns of anurans that exhibit a non-explosive breeding strategy

(Oseen and Wassersug 2002). Because anurans are poikiothermic, it is possible that

temperature would affect calling activity of anurans in the tundra, where summer freezes

are not uncommon.

No information exists regarding calling activity of boreal chorus frogs or wood

frogs in the tundra biome. Many ecological questions about anurans are addressed using

information derived from surveys, and most anuran surveys are rooted in detecting calls.

Therefore, understanding factors that affect calling activity in tundra anurans should

increase the effectiveness of research and monitoring efforts. Herein, I describe diurnal

and seasonal calling activity and the effects of temperature, humidity, and time of day on

calling activity of boreal chorus frogs and wood frogs in a tundra biome.

Study Area

Wapusk National Park, Manitoba, Canada is located on the southwest side of

Hudson Bay. The park boundary is 35 km southeast of the town of Churchill and the park


subarctic tundra biome, and encompassed a matrix of small upland ridges and lowland,







31

camp within the park, receives, on average, 436.1 mm of precipitation a year

(Environment Canada 2004). Few recreational uses occur in the park, except for

traditional uses such as hunting, trapping, fishing, and egg-collecting by local residents

and First Nations members.


research station located approximately 2 km from the Hudson Bay coastline south of




was conducted under Texas Tech University Animal Care and Use Committee permit

06021-05 and Parks Canada research permit: Wap-2005-518.

Methods

Eleven automated recorders were positioned at locations likely to contain anurans

based on characteristics of vegetation and water body. All recorders were situated >200

m apart. Each recorder was programmed to record ambient sounds for 3 minutes at 1.5-

hour intervals. I chose three minutes because most anuran species are detected within the

first 3 to 5 minutes of a survey (e.g., see Shirose et al. 1997). I also placed HOBO data

loggers (Onset Computer, Pocasset, Mass., H08-030-08; use of trade names does not

imply endorsement by the U.S. Geological Survey, the University of Minnesota, or Texas

Tech University) at each automated recorder site to record temperature and humidity in

concert with audio recordings.


32

Each automated recorder was left active for three days. On the third day, I

collected automated recorders in the evening, reviewed recordings, and then replaced

recorders the following morning. During review, I listened to each recording and noted

the species and number of anuran calls. At the end of the field season, I collected HOBO

data loggers and downloaded data on temperature, relative humidity, time, and day of

year (DOY) that corresponded with each 3-minute recording interval.

In order to extract anuran count data from the loggers, I assumed that the

automated recorders accurately depicted anuran calling activity. In Chapter I

demonstrated that anuran count data obtained by automated recorders and audile surveys

conducted by an observer differed for some species (Mannan et al., unpublished).

However, count data obtained from recorders was species specifically biased, suggesting

that count data obtained from recorders can be used as an accurate index to calling

activity, but not absolute abundance (Mannan et al., unpublished). My study focuses on

the effects of weather and seasonal variables on anuran calling activity not exact anuran

numbers. Therefore, for the purposes of this study I treated anuran count data obtained

from the automated recorders as an index to calling activity.

Statistical Analysis

My count data were regarded as Poisson-distributed random variables (e.g., see

Fitzmaurice et al. 2004). Variability among locations was not of interest in this study and

therefore the location effect was included in the model as a random nuisance variable.

Because of logistical considerations, data from the automated recorders were not


33

necessarily collected on the same days of the year. The resulting data set, therefore, was

analyzed using the methods of longitudinal data analysis (Fitzmaurice et al. 2004). I used

a linear mixed effects model to model anuran count data with a log link function, and

included location as a random nuisance variable, and day of year, relative humidity,

temperature, and time of day as independent variables. Data were analyzed with the

GLIMMIX procedure of SAS.

Results

In 2007, I placed 11 recorders at potential anuran-calling locations, and three of

these failed following a severe storm. I obtained data related to diurnal and seasonal

anuran calling patterns from the remaining eight recorders. Count data were collected at

eight locations from 30 May (DOY=150) to 9 July 2007 (DOY=190). Automated

recorders detected wood frogs between 30 May (DOY=150) and 2 July 2007

(DOY=183), and boreal chorus frogs between 11 June (DOY=162) and 5 July

(DOY=186) 2007 (Fig. 2.2). Both species exhibited calling patterns consistent with

explosive breeding behavior. Peak calling activity for boreal chorus frogs followed peak

calling activity for wood frogs by 12 days. Both species called 24 hours a day throughout

their breeding season, although peak calling times were afternoon and early morning (i.e.,

1200hrs – 0230 hrs; Fig. 2.2). Wood frogs called in temperatures ranging from -2.4 - 29.5

C. calling activity reassembled a normal distribution with lowest calling activity

occurring during temperature extremes (Fig. 2.2). Wood frogs called in relative humidity

ranging from 0% to 100% (Fig. 2.2). Increased calling activity was skewed towards lower


34

levels of humidity. Boreal chorus frogs called in temperatures ranging from -1.5 - 31.1C,

(Fig. 2.2). Calling activity increased as temperature increased. Boreal chorus frogs called

in relative humidity ranging from 0% to 100%, with peak calling activity occurring

during low levels of relative humidity (Fig. 2.2). Temperature and DOY explained a

significant amount of variation within the calling patterns of wood frogs (Table 2.1).

Relative humidity, temperature, DOY, and time of day explained a significant amount of

variation within the calling patterns of boreal chorus frogs (Table 2.2).

Discussion

Both wood frogs and boreal chorus frogs in my tundra study site exhibited calling

behavior consistent with an explosive breeding strategy. However, unlike other studies

conducted on explosive breeding anurans, in my study, colder temperatures were

associated with reduced calling activity of both species within the breeding season (e.g.,

see Oseen and Wassersug 2002). During late May and June, temperatures in northern

Manitoba can drop well below 0 C. Anurans are poikiothermic, and therefore cannot

remain active in all temperatures. The inability to remain active in low temperatures may

explain the association of calling activity of anurans and temperature on my study area.

Despite the positive association between wood frog calling activity and

temperature, I documented wood frogs calling during intervals when air temperature was

below freezing (Fig. 2.2). This may be attributed to a difference between air and water

temperature. Wood frogs spend a great deal of time in the water (Conant and Collins


35

1991). Water temperatures may have remained high enough to support anuran activity

during intervals when air temperature dropped below freezing.

For this study, DOY was designed to account for the effect of seasonal cues such

as day length or other unknown factors perceivable by anurans. A day is a fluctuating set

of environmental conditions occurring during a time interval. Within this varying set of

conditions are known (e.g., temperature) and unknown cues that trigger the start and stop

of anuran calling (e.g., see Conant and Collins 1991, Oseen and Wassersug 2002), which

should be especially important in explosive breeding anurans. While we cannot identify

specific factors causing the stat and stop of wood frog or boreal chorus frog breeding

seasons, the importance of DOY representing a seasonal effect on calling activity in my

study is consistent with the explosive breeding strategy of both anuran species.

One possible confounding factor related to the association between DOY and

calling patterns is that the automated recorders detected wood frogs on the first day of

recording. Therefore, it is likely that wood frog calling began before I was able to place

automated recorders in the field. If recorders were not in place to capture the beginning of

the calling season, then the first day of the recording interval would appear to be an

exaggerated abrupt beginning to the wood frog calling season. Therefore, some of the

variation in wood frog calling activity explained by DOY may have been an artifact of

the timing of the recorder placement. However, it is unlikely that calling began long

before automated recorders were activated. When recorders were activated there was still

snow around anuran breeding ponds. While wood frogs are known to call before the

complete thaw of breeding ponds, it is unlikely that calling began long before my arrival


36

(USGS 2002, Stebbins 1951). Also, wood frogs are known to begin breeding abruptly

throughout their breeding range and it seems likely that they began abruptly at my study

site as well (USGS 2002, Stebbins 1951).

Relative humidity and time of day also accounted for variation in the calling

pattern of boreal chorus frogs. The lowest detection levels of boreal chorus frogs began

around sunrise (0400 hrs) and continued through 1000 hrs (Fig. 2.2). Peak calling

occurred in the afternoon (1400 hrs and continued through the evening. These results

suggest that light intensity, related to time of day, may influence calling activity of boreal

chorus frogs, a common pattern among anurans (e.g., see Bridges and Dorcas 2000,

Oseen and Wassersug 2002). Avoidance of predators and thermoregulation have been

suggested as ultimate causes of the effect of light intensity on anuran calling activity.

Several bird species occurred in my study site during summer that likely prey on frogs,

including sandhill cranes (Grus canadensis), and many of those forage more vigorously

during morning hours (Iverson et al. 1985), a time when calling generally was

suppressed. Thus, predator avoidance seems a plausible explanation for reduced anuran

calling during morning hours in northern Manitoba.

There was a negative association between the calling activity of boreal chorus

frogs and humidity. Peak calling rate was at a relative humidity of about 30%. Peak

calling at low humidity levels is unusual for anurans (e.g., see Fogarty and Viella 2001,

Stevens et al. 2002). However, high humidity often accompanies precipitation. There are

several reasons for the boreal chorus frog to avoid calling during a precipitation event.

First, precipitation can interfere with sound transmission negating any reproductive


37

advantage to calling (Henzi et al. 1995). Second, in the tundra, summer precipitation can

come in the form of sleet and is often accompanied by large temperature swings. It may

be disadvantageous or physiologically impossible to call during such conditions. High

levels of humidity may cue a suppression of calling.


Calling activity of anurans, and thus the ability to detect them in surveys, varies

across regions and within seasons (Bridges and Dorcas 2000). Surveys of anurans in a

given region should, therefore, be timed according to local patterns. My results suggest

that breeding seasons of boreal chorus frogs and wood frogs overlapped, which would

facilitate monitoring both species simultaneously. Within the breeding season,

temperature influenced the calling activity of both species and time of day was related to

calling activity of boreal chorus frogs. Thus, conducting surveys during the evening and

in warmer temperatures may maximize survey efficiency. However, because the call

activity of the two species differed in their response to some climatic variables (e.g.,

relative humidity), species-specific surveys may result in higher detection levels for

individual species.


38

Figure

3.1. Study plots near Cape Churchill, Manitoba, where anuran surveys were conducted in

2007.


39

A.

30-May1-Jun

4-Jun7-Jun

9-Jun12-Jun

15-Jun17-Jun

20-Jun23-Jun

25-Jun28-Jun

1-Jul3-Jul

6-Jul9-Jul

Date

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Mea

n n

um

ber

of

anur

ans

dete

cted

per

site

Figure 3.2. Mean and standard deviation of the number of anurans detected as a function

of (A) date, (B) time of day, (C) temperature, and (D) relative humidity near Cape

Churchill, Manitoba, Canada, 2007 (□ = Wood frogs, ▲=Boreal chorus frogs).


40

B.

0:00 1:35 3:11 4:47 6:23 7:59 9:35 11:11 12:47 14:23 15:59 17:35 19:11 20:47 22:23 23:59

Time

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Mea

n n

um

ber

of

anu

ran

s d

ete

cte

d p

er s

ite

C.

-4.3 -2.0 0.4 2.8 5.1 7.5 9.9 12.2 14.6 16.9 19.3 21.7 24.0 26.428.8 31.1

Temp (C)

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Me

an n

um

ber

of

anu

ran

s d

ete

cte

d p

er

site

Figure 3.2. Continued


41

D.

-1.6 5.4 12.5 19.5 26.6 33.6 40.6 47.7 54.7 61.8 68.8 75.8 82.989.9 97.0 104.0

Relative humidity

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Mea

n n

um

be

r o

f an

ura

ns

det

ecte

d p

er s

ite

Figure 3.2. Continued

Table 3.1. Results of a regression analysis of a linear mixed effects model used to model

wood frog call activity, near Cape Churchill, Manitoba, Canada, 2007, (n= 1383).

Covariate Standard Error F P

RH (%) 0.00326 0.64 0.4250

Temp (C) 0.01300 12.95 0.0003

Day of Year 0.00703 123.81 <0.0001

Time 0.2193 1.49 0.2219


42

Table 3.2. Results of a regression analysis of a linear mixed effects model used to model

boreal chorus frog call activity, near Cape Churchill, Manitoba, Canada, 2007 (n= 1383).

Covariate Standard Error F P

RH (%) 0.00317 6.59 0.0103

Temp (C) 0.01192 6.72 0.0096

Day of Year 0.00955 0.0011 0.0011

Time 0.2250 0.0214 0.0214


43

CHAPTER IV

HABITAT ASSOCIATIONS OF BOREAL CHORUS FROGS (PSEUDACRIS

MACULATA) AND WOOD FROGS (RANA SYLVATICA) IN A TUNDRA BIOME

Abstract

Anuran populations in the subarctic tundra biome in northern Manitoba are being

impacted by multiple factors, including vegetation changes resulting from foraging

pressure by an increasing population of light geese. During the summers of 2006 and

2007, I surveyed 204 potential anuran breeding locations in two study plots in the tundra

biome within Wapusk National Park, Manitoba, Canada to assess anuran habitat

associations. I examined habitat selection and associations of wood frogs (Rana

sylvatica) and boreal chorus frogs (Pseudacris maculata) with regard to vegetation and

water quality. Both wood frogs and boreal chorus frogs selected sites where vegetation

was taller and had a higher composition of sedge (Carex spp.) and willow (Salix spp.).

Both species also selected sites with relatively low pH and conductivity (TDS). An index

of goose herbivory was negatively correlated with vegetation height and cover by sedge

and willow and positively correlated with pH and conductivity. Both wood frogs and

boreal chorus frogs were found more commonly in sites with less evidence of recent

goose herbivory.


44

Introduction

Tundra landscapes are being altered by both biological and physical factors. Over

the past two decades, mid-continent light geese [snow geese (Chen caerulescens) and

Ross’s geese (Chen rossii)] populations in northern Manitoba have increased at an annual

rate of 5-7% (Batt 1997, Jefferies and Rockwell 2002). Recently, the effects of this

population increase on tundra vegetation have received some attention. Increased grazing

has altered vegetation production as well as the overall vegetative composition in some

areas (Cargill and Jefferies 1989, Jefferies and Rockwell 2002). As goose populations

continue to grow and the extent of vegetation change increases, the potential for impacts

on other species in the tundra and their habitats also increases r (e.g., Sammler 2001).

Two anuran species, boreal chorus frogs (Pseudacris maculata) and wood frogs

(Rana sylvatica), are among species that may be negatively affected by goose herbivory

in the tundra biome. The range of wood frogs extends into Canada and Alaska, along the

northeastern seaboard in the United States, through the Great Lakes region and into the

northern Midwest states (USGS 2002, Stebbins 1951). The boreal chorus frog is the

northernmost of the chorus frogs with a range extending from portions of Arizona and

New Mexico through the Midwest, north into Alberta, Ontario, Saskatchewan, Manitoba,

and parts of the Northwest Territories (Koch and Peterson 1995, USGS 2002). Because

both species exist across a wide geographical range, specific habitat relationships in

many regions are unknown. However, both species use vegetation for cover and as

anchors for egg mass deposition, making attributes of vegetation likely important habitat

characteristics (Conant and Collins 1991, Crouch and Paton 2000).


45

In the tundra biome, there are few plants that grow very tall and that would

provide potential breeding vegetation for anurans. In tundra landscapes in northern

Manitoba, sedges (Carex aquatilis, C. rupestris, and C. glacialis) and small willows

(Salix planifolia, S. herbacea, and S. brachycarp) are the only plants that may provide the

shelter and structure needed for anuran egg mass deposition. Geese in some of these

tundra landscapes feed heavily on sedges, and the reduction and removal of sedges by

foraging geese may alter a tundra biome in three notable ways. First, both wood frogs and

boreal chorus frogs attach egg masses to aquatic vegetation, and reduction of sedges may

remove the cover and tall vegetative structure necessary for anuran egg mass deposition.

Second, removal of sedges may increase water pH at potential breeding sites; pH level is

a hydrological characteristic important to the survival of both wood frogs and chorus

frogs (Corn et al. 1989, Moore and Klerks 1998, Wikberg and Mucina 2002). Third,

foraging geese also potentially increase Total Dissolved Solids (TDS) in the water by

disturbing the substrate as they feed, or by removing vegetation and, thereby, altering the

filtration processes facilitated by wetland vegetation (Noller et al. 1994). Currently, the

influences of goose herbivory in tundra landscapes on anuran habitat associations are

unknown.

In 2006 and 2007, I conducted anuran surveys in a tundra landscape in northern

Manitoba to evaluate associations between anuran presence and vegetative structure,

water body depth, and environmental conditions [pH and TDS]. I also created an index

based on evidence of goose herbivory and evaluated associations between this index and


46

vegetation height, cover, and water quality. Finally I evaluated associations between

anuran presence and this index of goose herbivory.

Study Area

Wapusk National Park is located on the southwest side of Hudson Bay, Manitoba,

Canada. The park boundary is 35 km southeast of the town of Churchill and the park


subarctic tundra biome, and encompassed a matrix of small upland ridges and lowland,






camp out of which I conducted this study within the park, receives, on average, 436.1

mm of precipitation a year (Environment Canada 2004). Few recreational uses occur in

the park, except for traditional uses such as hunting, trapping, fishing, and egg-collecting

by local residents and First Nations members.


research station located approximately 2 km from the Hudson Bay coastline south of





47

was conducted under Texas Tech University Animal Care and Use Committee permit

06021-05 and the Parks Canada research permit Wap-2005-518.

Methods

In the summers of 2006 and 2007, I conducted anuran surveys at potential

breeding sites to evaluate associations between anuran occurrence and vegetative

structure and environmental conditions [pH and TDS] (see below). To select potential

breeding sites, I created two 12.6 km2 circular study plots; a northern study plot

established in 2006 and a southern study plot established in 2007. These study plots were

located approximately 4 km from Nestor One to avoid disturbance to goose nests under

observation as part of Canada goose (Branta canadensis interior) monitoring activities.

Study plots began at the coast of the Hudson Bay and had a diameter of 4 km that

extended inland (Fig. 3.1). I used ARCGIS [version 9.1] (ESRI, Redlands, Calif., USA;

use of trade names does not imply endorsement by the U.S. Geological Survey, the

University of Minnesota, or Texas Tech University) to randomly select 57 locations

within the northern plot and 60 locations within the southern plot. Buffer zones ensured

locations were not closer than 200 m from each other and the number of survey locations

was dictated by the time and logistical support available for survey activities. On the first

visit to each random location, I walked to the nearest potential anuran breeding site to

establish locations for surveys (described below). Because water bodies with depths ≤10

cm were likely to dry up within two weeks, I defined potential anuran breeding sites as

water bodies deeper than 10 cm.


48

To describe potential breeding sites, I first used a local coordinate system to select

two sample locations within each site. To create a local coordinate system, I estimated the

width and length of the water body that comprised the breeding site. I then used these

estimated distances as the axes of a hypothetical grid, with 1 m cells, that encompassed

the entire water body plus 0.5 m beyond the water body’s edge. I used a random number

generator to identify two grid intersections, which served as sample locations within each

potential breeding site. Some lakes in my study area lacked vegetation beyond the

shoreline and I never observed anurans calling from beyond the shoreline of these lakes.

Therefore, if the coordinates of a sample location fell in open water within a lake that

contained no vegetation beyond 1 m of the shoreline, all habitat variables (described

below) were measured from the point on the shoreline closest to the grid intersection. At

each sample location, I dropped a 1x1 m quadrat (constructed of rigid polyvinyl chloride

tubing) at my feet. In the case of a shoreline location, half of the quadrat was placed on

the shore and half in the lake. Within each quadrat, I measured pH, TDS, water depth at

two opposite corners of the quadrat, vegetation height at the four corners of the quadrat,

and the tallest vegetation within the quadrat. I chose these variables based on their

biological importance to anuran habitat selection and/or survival (Pierce et al. 1984, Corn

et al. 1989, Moore and Klerks 1998, Anderson et al. 1999, Crouch and Patton 2000, Kopp

and Eterovick 2006). For each potential breeding site, I used the two sample locations to

calculate an arithmetic mean of pH, TDS, vegetation height, and tallest vegetation, and

used these means in statistical analyses.


49

I also took a digital photo from 1.5 m directly above the quadrat to estimate

vegetation composition. Using Microsoft® Paint (Microsoft 2002; use of trade names

does not imply endorsement by the U.S. Geological Survey, the University of Minnesota,

or Texas Tech University), I placed a grid with 100 intersections on each photo. Using

Johnson (1987) as a key, I identified vegetation at each grid intersection to genus, and

estimated percent cover as the number of times a genus occurred under an intersection

divided by the total number of intersections. For each potential breeding site, I used the

photos from each sample location (n = 2) to calculate an arithmetic mean vegetation

composition by percent cover.

At every potential anuran breeding site, I also visually surveyed the entire site for

evidence of goose herbivory, and evaluated herbivory based on evidence of goose

foraging (Kerbes et al. 1990). I quantified evidence of goose herbivory into two foraging

types: “shoot pulling” and “grubbing”. “Shoot pulling” was evidenced by the presence of

uprooted sedges with the base of the plant removed. This is caused when geese uproot

vegetation, eat the basal tissue, and leave the rest of the plant. Shoot pulling was

separated into two groups; recent, or “new shoot pulling” and past, or “old shoot pulling”,

based on the color and condition of the uprooted vegetation. I classified uprooted floating

vegetation as new shoot pulling, and classified older and decomposing vegetation as old

shoot pulling. I similarly assessed grubbing in the substrate. Grubbing is characterized by

overturned small chunks of substrate, about the size of a goose bill. These measures of

goose foraging were designed to be correlated with grazing pressure. New shoot pulling

indicated only recent grazing and thus the smallest amount of grazing pressure. Old shoot


50

pulling represented a history of grazing, thus indicating heavier grazing pressure.

Grubbing normally occurs in areas lacking vegetation emergent from the substrate. I

assumed that in areas with no vegetation, above-ground vegetation had previously been

removed by geese, and therefore grubbing indicated the highest amount of grazing

pressure.

To document anuran presence or absence at each potential breeding site, I

conducted three surveys at ~ 6 day intervals. During each survey, I stood 5 m from the

edge of the potential breeding site and allowed one minute for anurans to acclimate to my

presence. I then recorded the number and species of anurans detected during a 3-minute

listening period. Following the 3-minute listening period I broadcasted anuran mating

calls in an attempt to increase detection rates (described below). I conducted all surveys

at each site from the same location. When I detected anurans during a survey, I

triangulated the position of the first detected anuran when calling continued long enough

for observers to estimate a bearing to the frog. Two observers standing ≥5 m apart

estimated the direction from which they heard the anuran and then walked in that

direction until their paths crossed at the estimated location from which the anuran called

(referred to as the triangulation location). I then measured vegetation in a quadrat

centered on the triangulation location, as described above. I used the triangulation

locations to represent habitat characteristics selected for by calling anurans within each

site.

In 2007, to supplement information on the characteristics of randomly located

potential breeding sites occupied by anurans, I -systematically searched both study plots


51

for presence of anurans. I repeatedly walked (>2 times) eight transects located at 1-km

intervals spanning study plots. When I detected anurans, I walked to the breeding site

from which the anurans were calling and triangulated an estimated calling location, as

described above. I then estimated the same habitat characteristics at the triangulation

location and at two random locations as I did for randomly located breeding sites

occupied by anurans.

I conducted surveys in two study plots (Fig. 3.1) during the course of the study. In

2006, between 30 May and 18 June, I conducted surveys at 57 random locations in Study

Plot One, established in 2006 north of Nestor One. In 2007, between 31 May and 11 July,

I repeated surveys at 27 randomly selected potential breeding sites surveyed in 2006, and

conducted anuran surveys at an additional 60 potential breeding sites in Study Plot Two,

established south of Nestor One. I conducted transect surveys (on both study plots) only

in 2007. Little empirical evidence exists about the rate at which vegetation is changing in

my study site, and although it is possible that anurans present and detected during surveys

in 2006 were present at some of the 27 sites resurveyed in 2007, I assumed my surveys

between years to be independent in statistical analyses.

Statistical Analysis

I evaluated anuran habitat associations at two levels; breeding site and within

breeding site. At the site level, I used t-tests to compare habitat characteristics of

unoccupied and occupied sites. To conduct this comparison, I used only data collected

from the two random sample locations of each site. To evaluate within-site associations,


52

from sites occupied by anurans, I used paired t-tests to compare habitat characteristics of

triangulation locations to the mean value of habitat characteristics of the two random

sample locations. I also used Fisher’s exact tests to further examine relationships between

presence of anurans and evidence of goose herbivory.

The variables I measured exhibited high levels of inter-correlation. Because my

variables were correlated and it is unclear which variables would be appropriate to

eliminate from my analysis, I used Principal Components Analyses (PCA) to assess

associations (McGarigal et al. 2000). I used PCA (STATISTICA [release 7]; StatSoft,

Tulsa, Okla., USA; use of trade names does not imply endorsement by the U.S.

Geological Survey, the University of Minnesota, or Texas Tech University) to extract

components from my data and identify characteristics associated with breeding sites

occupied by anurans. I selected components with eiganevalues above one to test for effect

on anuran presence (McGarigal et al. 2000) and conducted a multivariate analysis of

variance (MANOVA) to examine the associations between the selected components and

the presence of anurans at potential breeding sites. I then used a MANOVA to test for

within-model component significance.

I used PCA loading scores to evaluate the importance of variables within

components. The absolute value of the loading score of each variable within a component

indicates how strongly the component is associated with that variable (McGarigal et al.

2000). The higher the absolute value of a loading score, the stronger the association. As

the value chosen to warrant investigation or suggest importance to a component is


53

arbitrary, I used 0.5, a common value used to assess variable importance within a

component (McGarigal et al. 2000).

Results

Across both study plots and years, I detected anurans at 36 (25%) of 144 random

potential anuran breeding sites. I detected anurans at an additional 60 breeding sites by

walking transects through study plots. Using both methods, I detected a combined total of

48 potential breeding sites where I detected only wood frogs, 18 potential breeding sites

where I detected only boreal chorus frogs, and 30 potential breeding sites where I

detected both species.

For both wood frogs and boreal chorus frogs, sites where I detected frogs

contained taller vegetation and higher percent cover of vegetation than sites where I did

not detect frogs (Table 3.1). Occupied sites also contained lower pH and TDS than

unoccupied sites (Table 3.1). In addition, boreal chorus frogs were present at sites with

more cover and taller vegetation than wood frogs (Table 3.1). At the scale of location

within occupied sites, both anuran species were detected in areas with taller vegetation

and a higher percent composition of sedge and willow (Table 3.2). Both species were

detected more frequently at areas without evidence of goose herbivory; boreal chorus

frogs were negatively associated with all three measures of goose herbivory, whereas

wood frogs were significantly negatively associated with sites that had evidence of old

shoot pulling or grubbing (Table 3.3).


54

Most habitat variables were highly intercorrelated (Table 3.4). Therefore, I

extracted 10 components from the variables percent cover by sedge and willow, pH,

TDS, water depth, tallest vegetation, average vegetation height, new shoot pulling, old

shoot pulling, grubbing, and year. Based on eigenvalues >1, I selected components one

through four to test for effect on anuran presence. Approximately 69 percent of the

variation across breeding sites was incorporated in these four components (Table 3.5). A

model containing these four components was associated with both wood frogs

(MANOVA; Wilks’ Lambda = 0.75; F4,204 = 16.4, P < 0.001) and boreal chorus fogs

(MANOVA; Wilks’ Lambda = 0.70; F4,204 = 21.1, P < 0.001). Within-model significance

indicated that components one, three, and four were related to wood frog presence and

component one was related to boreal chorus frog presence (Table 3.6). Wood frog and

boreal chorus frog presence was negatively associated with component one (Fig. 3.2 and

Fig. 3.3).

Component one was associated with five variables; tallest vegetation received the

heaviest loading score followed by average vegetation height, TDS, percent cover by

sedge and willow, and pH. Component three was associated only with average vegetation

height. Component four was associated with new shoot pulling and with percent cover by

sedge and willow; new shoot pulling received the heaviest loading score (Table 3.7).

Sites with new and old shoot pulling or grubbing were negatively associated with

vegetation height and percent cover by sedge and willow, and positively associated with

pH and TDS (Fig. 3.4). When goose herbivory indices were modeled to represent

increasing levels of grazing pressure (i.e., no evidence of goose herbivory, presence of


55

only new shoot pulling, presence of new and old shoot pulling, and grubbing), increased

grazing pressure was negatively associated with average vegetation height (F3,204 = 13.1,

P < 0.001), tallest piece of vegetation (F3,204 = 22.4, P < 0.001), percent cover by sedge

and willow (F3,204 = 4.2, P = 0.006), and positively associated with pH (F3,204 = 2.70, P =

0.047) and TDS (F3,204 = 7.19, P < 0.001) (Fig. 3.4).

Discussion

On my study, boreal chorus frogs and wood frogs were positively associated with

percent cover of vegetation and vegetation height, although boreal chorus frogs tended to

favor areas with slightly taller vegetation than wood frogs. Both wood frogs and boreal

chorus frogs deposit egg masses on aquatic vegetation (Conant and Collins 1991) and

aside from sparse willows, sedge is the tallest vegetation offering structure appropriate

for egg mass deposition. Other species of chorus frogs also are associated with tall

vegetation (Anderson et al. 1999). Wood frogs are described as canopy generalists,

breeding in ponds that are both covered and not covered by tree canopy (Werner and

Glennemeier 1999), although associations between tree cover and ground cover have not

been assessed. In addition to providing appropriate structure for reproduction, higher

cover may also reduce predation risk from birds such as arctic terns (Sterna paradisaea)

or sandhill cranes (Grus canadensis). More extensive and higher cover may provide

better concealment.

The effect of pH on survival of anurans is population-dependant (Pierce 1985). In

my study area I found negative relationships between anurans and pH, but all pH levels


56

were within the tolerance ranges of wood frogs and other chorus frogs (Pierce et al. 1984,

Corn et al. 1989). Wikberg and Mucina (2002) demonstrated that in sedge-dominated

aquatic environments, removal of sedge results in an increase in water pH. On my study

area, it may be that anurans are associated with high levels of vegetative cover, which

may have lower pH, rather than being associated with lower pH itself.

Both Canada geese and light geese return annually to the tundra around Cape

Churchill to nest. Light goose numbers are increasing (Batt 1997, Jefferies and Rockwell

2002), and large numbers of light geese migrating to more northerly breeding areas

forage in the tundra near Cape Churchill (Jefferies and Rockwell 2002). Goose herbivory

has had dramatic effects on tundra vegetation near Cape Churchill, and in some areas, has

resulted in almost complete removal of vegetation (Jefferies and Rockwell 2002).

Currently there are no standard indices for goose herbivory in a tundra biome. The

indices to goose herbivory that I used are based on the pattern of impacts on tundra

vegetation from goose foraging described in Krebs et al. (1990). Sites with only evidence

of new goose herbivory should display the least severe effects of grazing, and have been

impacted least by geese. Sites that contained evidence of old shoot pulling likely had a

longer history of grazing and the effects of grazing should be more severe. Grubbing

occurs in areas with extensive goose foraging activity because grubbing usually occurs in

areas with little above-ground vegetation. This categorization of the extent and history of

goose herbivory appeared to reasonably depict grazing intensity, as sites with old shoot

pulling, and presumably a longer history of grazing, contained shorter vegetation and

higher pH values than sites with no evidence of goose herbivory. Sites with evidence of


57

grubbing contained less cover and shorter vegetation than sites with old shoot pulling.

Taller vegetation at sites with new shoot pulling may indicate that geese have only

recently begun to use these areas, or that grazing pressure has not been high enough to

result in measurable effects on vegetation. The patterns of vegetative cover and pH that I

observed, suggest that the index I used to quantify goose herbivory reasonably reflects

past levels of grazing pressure.

Presence of both wood frogs and boreal chorus frogs was negatively related to

evidence of goose herbivory. Because vegetation height and cover are important to both

frog species, it is not surprising that there were fewer frogs where there was evidence of

more extensive herbivory. Prolonged and heavy grazing by geese can significantly alter

the structure and composition of the vegetation that anurans select for breeding sites

(Jefferies and Rockwell 2002). Specifically, increased foraging by geese may reduce the

amount of sedge, leading to an alteration or loss of habitat important for wood frogs and

boreal chorus frogs.

One surprising result was the relationship between new shoot pulling and wood

frog presence suggested by the PCA analysis. However, given the strong negative

association between wood frogs and goose herbivory, it is unlikely new shoot pulling

attracts wood frogs. Instead, new shoot pulling likely occurs in sites where sedges are still

relatively abundant, and these areas may already be occupied by wood frogs when new

shoot pulling takes place.

I also observed a negative association between anuran presence and higher levels

of conductivity (TDS). Reasons for the association are unclear. However, higher


58

conductivity is correlated to increased grazing pressure, which is associated with

decreases in extent of vegetative cover. Vegetation in wetlands filters inorganic and

organic substances from water. A decrease in vegetation may hinder these processes,

increasing inorganic material in the water, and resulting in higher levels of conductivity

(TDS). Therefore, it’s likely that the negative association between anuran presence and

increasing TDS is an artifact of the loss of vegetation due to goose herbivory.


Vegetation is important to both anuran species present in the tundra landscape in

northern Manitoba and elsewhere (Anderson et al. 1999, Werner and Glennemeier 1999).

Wood frogs and boreal chorus frogs appear to select for sites with taller vegetation and

higher percent vegetative cover. Increased foraging pressure from goose herbivory may

negatively impact both species of anuran inhabiting the tundra biome near Cape

Churchill, Manitoba. The extent of effects of goose foraging in this landscape, especially

in the freshwater sedge-meadow habitats, has not been adequately assessed. However, it

is likely that as grazing pressure increases the number of sites suitable for anuran

breeding will also decrease.A more through examination of resulting vegetation damage

from grazing pressure must be conducted. I also recommend that sticker population

management actions be taken regarding light geese.


59

Figure 4.1. Study plots near Cape Churchill, Manitoba, where anuran surveys were

conducted in 20067 and 2007.


60

Table 4.1. Mean values of habitat variables at detection and non-detection sites for wood

frogs and boreal chorus frogs near Cape Churchill, Manitoba, 2006-2007.

(Bolded values indicate statistical difference between detection and non-detection sites at

the 0.05 alpha level: t-tests. a Indicates values are significantly different between species

at the 0.05 alpha level; t-tests.).

Wood Frog Boreal Chorus Frog

Variable Wood Frog

(n = 78) Non-detection

(n = 126)

Boreal Chorus Frog

(n = 48)

Non-detection (n = 156)

Percent Composition

of Sedge and Willow

74.0 46.3 72.5 52.1

pH

7.6 8.0 7.6 7.9

TDS (Total Dissolved

Solids) 137.6 178.1 110.2 178.7

Tallest Vegetation

(cm) 36.2 a 24.3 49.4a 22.5

Average Vegetation Height (cm)

9.0 a 4.7 15.2 a 3.6


61

Table 4.2. Mean values of percent cover, vegetation height, tallest piece of vegetation,

pH, and TDS of triangulation locations and corresponding breeding sites near Cape

Churchill, Manitoba, 2006-2007. (Bolded numbers indicates statistical difference at the

0.05 alpha level; t-tests.)

Wood Frog Boreal chorus frog

Variable Triangulation

Location (n = 48)

Breeding Site (n = 48)

Triangulation Location (n = 38)

Breeding Site (n = 38)

Percent Composition

of Sedge and Willow

87.5 77.5 89.2 80.0

pH

7.5 7.5 7.6 7.7

TDS (Total Dissolved

Solids) 126.0 123.7 116.55 107.2

Tallest Vegetation

(cm) 51.3 34.4 84.4 54.2

Average Vegetation Height (cm)

14.8 7.7 31.4 17.9

Te

xas

Te

ch U

nive

rsity

, Rob

ert N

. Man

nan,

May

, 200

8

62

Table 4.3. Number of sites with and without anuran detections that contained evidence of goose herbivory near Cape

Churchill, Manitoba, 2006-2007.

Evidence of New Shoot

Pulling

No Evidence of New Shoot

Pulling

Fischer’s Exact Test

Results (P-

value)

Evidence of Old Shoot

Pulling

No Evidence

of Old Shoot

Pulling


Results (P-

value)

Evidence of New

Grubbing

No Evidence

of Grubbing


Results (P-

value)

Wood Frog

Detections 54 24 14 64 24 54

No Wood Frog

Detections 85 41

0.66

51 75

0.0005

64 62

0.003

Boreal Chorus

frog Detections

23 25 6 42 7 62

No Boreal Chorus Frog

Detections

116 40

0.0007

58 97

0.0006

81 75

<0.0001

Te

xas

Te

ch U

nive

rsity

, Rob

ert N

. Man

nan,

May

, 200

8

63

Table 4.4. Correlation coefficients and P-values (in parentheses) of measured habitat variables at potential breeding sites of boreal

chorus frogs and wood frogs near Cape Churchill Manitoba 2006-2007 (n= 204).

Habitat

Variables Percent Cover

pH TDS New Shoot Pulling

Old Shoot Pulling

Grubbing Water Depth

Tallest Veg.

Veg. Height

Year 0.09

(0.216) -0.27

(<0.001) -0.34

(<0.001) 0.07

(0.344) -0.35

(<0.001) 0.26

(<0.001) -0.44

(<0.001) 0.11

(0.133) 0.09 0.204

Veg. Height 0.17 (0.017)

-0.19 (0.007)

-0.26 (<0.001)

-0.13 (0.067)

-0.13 (0.066)

-0.18 (0.010)

0.10 (0.174)

0.84 (<0.001)

X

Tallest Veg. 0.29 (<0.001)

-0.25 (<0.001)

-0.33 (<0.001)

-0.17 (0.015)

-0.17 (0.013)

-0.26 (<0.001)

0.12 (0.094)

X

Water Depth

0.08 (0.233)

-0.05 (0.440)

-0.05 (0.453)

-0.05 (0.482)

0.12 (0.088)

-0.31 (<0.001)

X

Grubbing -0.22 (0.002)

0.11 (0.117)

0.18 (0.008)

0.32 (<0.001)

0.02 (0.772)

X

Old Shoot Pulling

-0.24 (0.001)

0.17 (0.017)

0.28 (<0.001)

0.22 (0.002)

X

New Shoot Pulling

0.03 (0.722)

0.03 (0.677)

0.17 (0.013)

X

TDS -0.29 (<0.001)

0.29 (<0.001)

X

pH -0.39 (<0.001)

X

Percent Cover

X


64

Table 4.5. Eigenvalues of a correlation matrix and the % variation of habitat variables

explained in models of habitat associated with anuran locations near Cape Churchill,

Manitoba, 2006-2007.

Component Eigenvalue

% Total Variation Explained

Cumulative % Variation Explained

1 2.75 28.5 28.5

2 1.86 18.6 46.1

3 1.18 11.6 57.9

4 1.15 11.5 69.4


65

Table 4.6. Results of a post-hoc MANOVA test for within-model significance when

predicting anuran presence near Cape Churchill, Manitoba, 2006-2007 (n = 202).

Wood Frog Boreal Chorus Frog

Degrees

of Freedom

F P Degrees

of Freedom

F P

Intercept 1 163.87 <0.0001 Intercept 1 87.21 <0.0001 Component

1 1 41.09 <0.0001 Component

1 1 80.53 <0.0001

Component 2

1 0.07 0.785923 Component

2 1 0.319 0.667791

Component 3

1 6.67 0.0109 Component

3 1 0.00 0.241743

Component 4

1 18.87 <0.0001 Component

4 1 2.57 0.270363


66

-4 -3 -2 -1 0 1 2 3

Component one

0

1

Woo

d fr

og p

rese

nce

Figure 4.2. The relationship between component one and wood frog detection, depicted

by a logistic regression line near Cape Churchill, Manitoba, 2006-2007.


67

-4 -3 -2 -1 0 1 2 3

Component one

0

1B

orea

l Ch

oru

s fr

og p

rese

nce

Figure 4.3. The relationship between component one and wood frog presence, depicted

by a logistic regression line near Cape Churchill, Manitoba, 2006-2007.


68

Table 4.7. Loading scores of variables within Principal Components of habitat models

describing anuran locations near Cape Churchill, Manitoba, 2006-2007.Bolded numbers

indicate loading scores of absolute value >0.5.

Variable

Component 1 Component 2 Component 3 Component 4

Percent Sedge and

Willow -0.558303 0.028580 0.287488 0.503835

pH 0.545991 -0.187277 -0.213056 -0.458068

TDS 0.649573 -0.179072 -0.215902 0.019466

New Shoot Pulling

0.317061 0.244211 -0.360346 0.702940

Old Shoot Pulling

0.461116 -0.392509 -0.336038 0.295282

Grubbing 0.401067 0.595045 -0.338211 0.095668

Average Water Depth

-0.124618 -0.711388 0.138510 0.276933

Tallest Piece of

Vegetation -0.796087 -0.178313 -0.493451 -0.070232

Average vegetation

Height -0.708621 -0.171146 -0.616651 -0.116700

Year -0.311491 0.810436 -0.030130 -0.055378


69

Figure 4.4. Means and 95% confidence intervals of (A) average vegetation height, (B) %

cover by sedge and willow, (C) average height of tallest vegetation, (D) TDS, and (E)

pH, with respect to evidence of goose herbivory near Cape Churchill, Manitoba, 2006-

2007.


70

Figure 4.4. Continued.


71

Figure 4.4. Continued.


72

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emerging and breeding in playa wetlands. Wildlife Society Bulletin 27(3):759-769.

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distribution and habitat associations in Wapusk National Park, Cape Churchill, Manitoba: 2005 summary report. Minnesota Cooperative Fish and Wildlife Research Unit, St. Paul, Minnesota, USA. 20pp.

Batt, B.D.J., editor. 1997. Arctic ecosystems in peril: report of the Arctic Goose Habitat

Working Group. Arctic Goose Joint Venture Special Publication. United States Fish and Wildlife Service, Washington, D.C. and Canadian Wildlife Service, Ottawa, Ontario, Canada.

Benedix, J.H. Jr. and P.M. Narins. 1999. Competitive calling behavior by male treefrogs,

Eleutherodactylus coqui (Anura: Leptodactylidae). Copeia 1999(4):1118-1112. Berven, K. 1990. Factors affecting population fluctuations in larval and adult stages of

the wood frog (Rana Sylvatica). Ecology 71(10):1599-1608. Boal, C.W. and D.E. Andersen. 2003. Pilot study of boreal chorus frog and wood frog

distribution and aquatic habitat conditions at Cape Churchill, Manitoba. Unpublished report to Wapusk National Park and the Mississippi Flyway Council. Minnesota Cooperative Fish and Wildlife Research Unit, St. Paul, Minnesota, USA.

Bridges, A.S. and M.E. Dorcas. 2000. Temporal variation of anuran calling behavior:

implications for surveys and monitoring programs. Copeia 2000(2):587-592. Burmeister, S., W. Wilczynski, and M J. Ryan. 1999. Temporal call change and prior

experience affect graded signaling in the cricket frog. Animal Behaviour 57(3):611-618.

Cargill, S.M. and R.L. Jefferies. 1984. The effects of grazing by lesser snow geese on the

vegetation of a sub-arctic salt marsh. Journal of Applied Ecology 21(2):669-686. Conant, R. and J.T. Collins. 1991. A field guide to reptiles and amphibians: eastern and

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APPENDIX A

AUTOMATED RECORDER COMPONENTS

Components in the automated loggers I used included a digital voice recorder

(Olympus vn-2000), digital timer (American Deer Hunter 30556), microphone (Olympus

me-15), 12-volt battery (Panasonic LC-R121R3P), and a solar panel (Sun Force 77796).

(Fig. 4.1 and Fig. 4.2) All components except the solar panel and microphone were

housed inside of a metal box. The microphone protruded from the box through a hole. A

chicken wire frame encompassed the entire the box, to reduce mammalian disturbance.

The solar panel was fixed to a chicken wire frame. Circuitry was constructed at Texas

Tech University (Fig. 4.3).

Automated recorders were originally programmed to broadcast advertisement

calls after the 3-minute recording interval and then conduct another 3-minute recording

interval. However, the speakers failed to function properly and automated recorder

broadcasts were never conducted in the field.


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Figure 5.1. Diagram of automated recorder components near Churchill, Manitoba, 2006-

2007.


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Figure 5.2. Photograph of automated recorder components near Cape Churchill,

Manitoba, 2006-2007.


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Figure 5.3. Control board for automated recorder near Cape Churchill, Manitoba, 2006-

2007.


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