ORNITOLOGIA NEOTROPICAL 15 (Suppl.): 349–355, 2004© The Neotropical Ornithological Society

AUSTRAL MIGRATION IN COLOMBIA: THE STATE OF KNOWLEDGE, AND SUGGESTIONS FOR ACTION

F. Gary Stiles

Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Bogotá D.C., Colombia. E-mail: fgstilesh@unal.edu.co

Resumen. – Migración austral en Colombia: el estado de conocimiento y sugerencias sobre cómoproceder. – Comparada con la migración boreal, la migración austral ha sido poco estudiada en Colombia.Esta situación refleja diferencias entre los tamaños y diversidades de las áreas “fuentes” de las aves migra-torias, distribuciones de aves migratorias vs las de observadores potenciales, oportunidades para financia-miento y afinidades taxonómicas con relación a los residentes tropicales. Presento una reseña breve delestado de conocimiento de la migración austral en Colombia, ilustrado con dos ejemplos que muestran lasmuchas preguntas todavía sin contestar sobre la migración austral en general. Para contestar estas pregun-tas será necesaria la cooperación internacional, para la cual los países “fuente” del sur de Sudamérica estánmejor situados para tomar la delantera.

Abstract. – Compared to boreal migration, austral migration has been little studied in Colombia. Thisreflects differences between the migration systems in the size and diversity of source areas of migrant avi-faunas, distributions of migrants vs potential observers, funding opportunities and taxonomic affinities rel-ative to tropical residents. I present a brief review of the state of knowledge of austral migration inColombia, illustrated with two examples, to highlight the many unanswered questions regarding australmigration in general. International cooperation will be the key to answering these questions, for which thesource countries of southern South America are best situated to take the lead. Accepted 6 February 2004.

Key words: Austral migration, Colombia, monitoring, Neotropical birds, South America.

INTRODUCCIÓN basin. Effectively, Colombia is the gateway to

Colombia, in the northwestern corner ofSouth America, is at the crossroads of the twogreat migration systems of the New World,receiving postbreeding migrants from thehigher latitudes of both northern and south-ern hemispheres. Southwards and eastwardsfrom Colombia in South America, australmigrants predominate, but few of these crossthe northern Andes or reach Middle or NorthAmerica (Stiles & Skutch 1989, A.O.U. 1998).From the eastern Andes westwards andnorthwards boreal migrants are prominent,but relatively few species extend in apprecia-ble numbers into or beyond the Amazon

South America for boreal migrants arrivingvia Central America and many of those cross-ing the Caribbean, but it is the end of the line(or the back door) for austral migrants.

REVIEW OF AUSTRAL MIGRATIONIN COLOMBIA

The boreal migrants are by far the betterknown and more studied in Colombia. This ispartly due to differences between the sourceareas and the avifaunas themselves. NorthAmerica is far larger and more diverse thansouthern South America, extending muchfurther polewards. The avifauna is corre-

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spondingly more diverse, with over 300 spe-cies migrating to the Neotropics during theirnonbreeding period, as compared to only c.230 austral migrant species (Chesser 1994,A.O.U. 1998). This disparity is heightened bythe fact that half or more of the australmigrants reach tropical latitudes scarcely ornot at all (Joseph 1997). In Colombia, overfour times as many species of boreal as australmigrants (approx. 175 vs 43) have beenrecorded (Hilty & Brown 1986).

The disparity in knowledge of boreal vsaustral migrants in Colombia is heightened bytheir distributions. Most austral migrantsoccur east of the eastern Andes, especially inAmazonia: these are the most thinly popu-lated parts of the country with no large cities,universities or museums, and observers arelikewise few and usually are present for rela-tively short periods. Much of what we knowabout austral migrants in Colombia is due to ahandful of North Americans who resided forvarying periods in eastern Colombia, often asmembers of the Peace Corps, in the 1970’sand early 1980’s (e.g., Gertler, MacKay andLemke). By contrast, boreal migrants mostlyoccur in the Andes, the Magdalena and Caucavalleys and the northern coastal plain andfoothills where most of the population ofColombia resides, including virtually all largecities, universities and museums, and wherethe vast majority of observations have beenmade and specimens collected. A further dif-ference between source areas also contributesto the knowledge gap: the disparity in thesizes and wealth of their respective scientificestablishments. There has been a long tradi-tion of North American (and European) orni-thologists working in tropical South America(I note here the pioneering work of McNeiland his colleagues in Venezuela for australmigrants), but no corresponding influx ofworkers from, say, Argentina or Chile. More-over, a recent upsurge in concern for the fatesof boreal migrants during the northern winter

has resulted in a similar increase in Nearcticfunding for (mostly) North American orni-thologists to study these migrants in the Neo-tropics (note the studies of Greenberg,Ramos, Rappole, Sherry, Wunderle, Lynch,Joseph, Chipley and many others). No com-parable phenomenon has permitted fundingof studies of austral migrants, except possiblywithin the boundaries of Brazil.

Austral migration is also not as conspicu-ous as boreal migration in most of Colombia.Because the source area is so much smaller,the volume of austral migrants is far lower,and the areas where they mostly occur includesome of the most complex and species-richavifaunas and tallest, most diverse evergreenforests in the world. Problems of taxonomyand identification also complicate the study ofaustral migrants. Fully half of the australmigrant species in Colombia also have resi-dent populations (though in about half ofthese, different subspecies are involved). Nofewer than six species occur as both borealand austral migrants and residents. Forinstance, all three forms of the Red-eyedVireo (Vireo olivaceus) have been taken inOctober and November in the Leticia area ofthe Colombian Amazonia: the boreal migrantolivaceus, the austral migrant chivi and the resi-dent solimoensis. Compounding these difficul-ties, many austral migrants belong to generain which identification of species in the field(or even in the hand) is notoriously difficult,such as Elaenia and Myiarchus flycatchers orChaetura swifts.

Knowledge of austral migration inColombia is thus largely limited to data fromspecimens collected opportunistically, mostlyover the last 50 years by a few resident orni-thologists, especially at the Instituto de Cien-cias Naturales (Olivares, Borrero, Romeroand colleagues), the Museo de La Salle (Hno.Nicéforo María) and the Universidad del Valle(Borrero, Catano), and the observations of afew long-term visitors like J. V.Remsen (Leti-

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cia area), S. L. Hilty (various areas) and S.Fisher (the llanos), as well as the Peace Corpsobservers mentioned above. These data suf-fice to permit a brief overview of Colombia’saustral migrants (excluding seabirds), as fol-lows: 1) four species of diurnal raptors (onefalcon, three accipitrids, two of which are rare

and of rather uncertain status; 2) four water-birds (two rails, a gull and a skimmer); 3)fourCoccyzus cuckoos; 4) two Chaetura swifts; 5) 19tyrannid flycatchers including six species ofElaenia, three Tyrannus; 6) five swallows,including three species of Progne; and 7) twoSporophila seedeaters.

FIG. 1. Distribution of specimen records of Short-billed Elaenias (Elaenia parvirostris) in Colombia accord-ing to period of year. Data from Instituto de Ciencias Naturales and Project BIOMAP.

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The austral migrant contingent in Colom-bia thus seems reasonably representative ofthe austral migrant system as a whole in termsof taxonomic composition, notably in thepredominance of Tyrannidae (cf. Chesser1994). For only a handful of these are enoughspecimens or other data available to permit areconstruction of their status in Colombia(though in some cases, more questions areraised than answered). Two such cases are dis-cussed forthwith.

Short-billed Elaenia. The Short-billed Elaenia(Elaenia parvirostris) is perhaps the australmigrant best represented in Colombian col-lections; data from 68 specimens fromInstituto de Ciencias Naturales and projectBIOMAP are presented here (Fig. 1). Idivide these records into three periods: arrival(March–May), wintering (June–August),and departure (September–November). All

records for the arrival period are for east ofthe Andes and, mainly, for the Andean foot-hills and adjacent lowlands, but cover theentire latitudinal range from the Amazon toArauca. Evidently the species can cover thedistance from southern to northern Colombiawithin a few weeks. Most birds for which dataare available do not show large fat depositsand most are in fresh plumage. During thewintering period, a minority of the birdsapparently undergo a complete molt (are themajority first-year birds?) and at least a fewcross the Andes, where they may reach sitesas far west as the Cauca valley, and as farnorth as the Caribbean coast, and even someoffshore islands. Records from the departureperiod are from the eastern Magdalena valleyor east of the Andes, and again rather fewbirds seem to have accumulated appreciablefat reserves (but I emphasize that for only aminority were data on body mass, skull ossifi-

FIG. 2. Distributions of specimen records of migratory races of Fork-tailed Flycatchers (Tyrannus savanna)in Colombia: T. s. monachus is a boreal migrant, T. s. savanna is an austral migrant.

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cation and fat taken). In Venezuela, manyindividuals had accumulated enough fat by thetime of their southwards departure to permitthem to reach their breeding areas by a non-stop flight (McNeil & Carrera 1968). Datafrom an intensive mist-netting study at a sitein eastern Venezuela (McNeil 1982, Tarroux etal. 2003) document great year-to-year varia-tion in numbers of austral (as well as boreal)migrants wintering at or passing through agiven site, probably reflecting variations inrainfall and food supplies. This points up afurther difficulty in interpreting the specimendata, since in any given year one or a fewspecimens, or none, were taken (more areflection of the presence of collectors thanof the birds).

Fork-tailed Flycatcher. A somewhat more com-plicated case is that of the Fork-tailed Fly-catcher (Tyrannus savana) (Fig. 2). In thisspecies, 1) a resident race (sanctaemartae)breeds in the Caribbean coastal plain, 2) aboreal migrant (monachus) occurs widely fromAugust or September through May (andapparently year-round in the llanos of north-eastern Colombia) with most birds moltingbetween about November and January, and 3)an austral migrant (savana) occurs in easternColombia between about April through Octo-ber, during which time most birds molt (cf.McNeil & Carrera 1968 for data from Vene-zuela). There are also a number of interestingsight records of apparently migrating flocks(many summarized by Hilty & Brown, 1986)which are difficult to interpret since the sub-species was not determined. A detailed analy-sis is perhaps not warranted here, but severalinteresting facts were brought to light in thepresent examination of c. 110 specimens andother records: 1) both northern and southernmigrants may occur together in certainmonths in the llanos; 2) monachus apparentlybreeds in the llanos (and may also do so in theCauca valley) between about March and May;

and 3) records of savana for October in thedeparture period are concentrated in theBogotá savanna of the eastern Andes! Clearly,much more remains to be learned regardingthe movements of this species.

Other species. Fragmentary data for a few otherspecies also suggest patterns, to be evaluatedwith more data. For instance, the Gray Elae-nia (E. strepera), is known from a few recordsin extreme southeastern Colombia and manyfrom southern and eastern Venezuela (cf.McNeil 1982): does it avoid the open countryof the llanos? The Yellow-browed Tyrant(Satrapa icterophrys) is a well-known migrantand winter resident in southern and easternVenezuela, including the eastern llanos, yetthere is only one record for adjacent Colom-bia (Arauca). Does it migrate through easternSouth America and spread westward onlyupon reaching the base of the Andes?

QUESTIONS AND SUGGESTIONS

Some of the more interesting questionsregarding austral migration that could bestudied in the coming years are the following:Do austral migrants have specific, well-defined migration routes or “flyways” as domany boreal migrants? Do they use specificstopover sites? How constant are arrival anddeparture dates for austral migrants from yearto year? Do austral migrants lay down fatdeposits comparable to those of borealmigrants? How do their diets change before,during and after migratory periods? To whatextent do specific habitats (e.g., riverine suc-cessional habitats in Amazonia) and land-forms (e. g., the Andes) affect movementpatterns and areas of residence? Do breedingand molt cycles show similar relations tomigratory movements as in boreal migrants?Are any austral migrants threatened primarilyby problems on their winter ranges?

Answering these questions will require

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taking a number of steps, some of which willrequire international cooperation amongSouth American countries. A series of strate-gically located monitoring sites should be setup in each country (and where two countriesmeet, possible international sites could beestablished, as in the Leticia-Tabatinga area ofColombia-Brasil). Long-term monitoring andbanding programs will be needed, which inturn will require a common data base andbanding scheme for all the countries involved.To insure uniform criteria for taking data indifferent countries, a series of regional train-ing workshops should be instituted. One out-put of such workshops might be a series ofidentification manuals that detail methods fordistinguishing austral migrants from similarresident congeners – as mentioned above, thisproblem is much more severe for austral thanfor boreal migrants.

From my experience in observing andbanding boreal migrants over many years inCosta Rica (Stiles 1994) and Colombia (andmuch more limited experience with australmigrants in Colombia), I venture to offer sev-eral suggestions toward implementing thesesteps. The monitoring sites should containvaried vegetation of different heights: thoughmigrants must occur in forested areas (or per-force pass through them while migratingthrough the Amazon basis), they are muchmore obvious (and bandable!) in nonforestareas like savannas or second-growth scrub.Because most migrants in forest areas may befound in the canopy and thus all but impossi-ble to see, count or capture, vegetation of thestudy area may require management to main-tain an adequate extension of early succes-sional growth. Young riverine succession maywell constitute an important habitat formigrants in the Amazon basin, and should beincluded in sites to be monitored insofar aspractical.

With respect to training programs, I thinkthat it will be important to have workshops

based at least initially in the source countriesfor austral migrants, i.e., where these speciesbreed. This will facilitate the initial familiar-ization with these species by observers andbanders from other countries, who can thenreturn better prepared to distinguish them. Itwill be important to include museum as wellas field and laboratory work, to permit learn-ing of the different plumages of australmigrants (another advantage of source coun-tries for such workshops, as their museumsare more likely to have good series of thesespecies). Once they are thoroughly familiarwith the austral migrants, workers from othercountries can prepare identification manualsfor distinguishing these species from confus-ingly similar resident species of their respec-tive regions. A final suggestion is that it mightbe more feasible to fund projects on australmigrants by combining them with others onboreal migrants (which at present are muchmore likely to receive funding, since thesource countries for austral migrants aremuch less willing or able to fund suchprojects in other countries). In the long term,however, it seems inevitable that if we are tomake significant progress in understandingaustral migration, the austral countries, wherethese species breed, will have to take the ini-tiative. Just as North American leadership inthe study of boreal migrants has stemmedfrom a concern for the welfare of “their”breeding birds, so might the authorities in theaustral countries become convinced of theimportance of funding projects on the migra-tion and wintering biology of “their” birds.Ultimately, a major education program toinform public servants on the importance ofconservation of austral migrants, may be thebest way to assure the study and conservationof these species.

ACKNOWLEDGMENTS

I am grateful to Doug Levey, Alex Jahn and

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Kim Smith for the opportunity to attend thissymposium, and to the National ScienceFoundation and the Instituto Humboldt forfinancial support. Andrea Morales and DianaArzuza of Project BIOMAP helped to makeavailable the data and María Isabel Morales ofConservation International-Colombia helpedwith the georeferencing and analysis. The col-lection of the Instituto de Ciencias Naturalesprovided the basic data, and I thank JairoSánchez and Arturo Rodríguez for curatorialassistance. Loreta Rosselli helped in the prep-aration of this presentation, and in manyother ways.

REFERENCES

A.O.U. 1998. Checklist of North American Birds,.7th ed. American Ornithologists’ Union, Wash-ington, D.C.

Chesser, R. T. 1994. Migration in South America: areview of the austral system. Bird Conserv. Int.4: 91–108.

Hilty, S. L. & W. L. Brown. 1986. A guide to thebirds of Colombia. Princeton Univ. Press, Prin-

ceton, New Jersey.Joseph, L. 1997. Towards a broader view of Neo-

tropical migrants: consequences of a re-exami-nation of austral migrants. Ornitol. Neotrop.8:31–36.

McNeil, R. 1982. Winter resident repeats andreturns of austral and boreal migrant birdsbanded in Venezuela. J. Field Ornithol. 53:125–132.

McNeil, R., & M. Carrera de Itriago. 1968. Fat dep-osition in the Scissors-tailed Flycatcher (Mus-civora t. tyrannus) and the Small-billed Elaenia(Elaenia parvirostris) during the austral migrationperiod in northern Venezuela. Can. J. Zool. 46:123–128.

Stiles, F. G. 1994. A study of fall migration ofNearctic-breeding landbirds in central CostaRica. Bird Conserv. Int. 4: 71–90.

Stiles, F. G., & A. F. Skutch. 1989. A guide to thebirds of Costa Rica. Cornell Univ. Press, Ithaca,New York.

Tarroux, A., R. McNeil, & P. Legendre. 2003. Influ-ence of rainfall on the composition of a tropicalavian assemblage in northeastern Venezuela.Ecotropica 9: 15–31.

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