Hayes, F. E., and J. A. Fox. 1991. Seasonality, habitat use, and flock sizes of shorebirds at the Bah�a de
Asunci�n, Paraguay. Wilson Bulletin 103:637-649.
Abstract.--Twenty species of shorebirds were recorded during 47 censuses along the margins of the Paraguay River at the Bah�a de Asunci�, Paraguay, from 1987-1989. The numbers of most Nearctic migrants (15 species) were higher during boreal fall than during spring, presumably due to flooding of the Paraguay River basin during spring and summer; numbers of Neotropical residents (five species) peaked during December-March. The abundance of most shorebirds, especially Neotropical species, was correlated negatively with water level, an inverse measure of habitat availability. Interannual variation in abundance appeared to be related to local hydrological conditions. Each species differentially exploited a given habitat, providing evidence of habitat partitioning. Intraspecific flock sizes of most species were correlated with abundance and, by inference, seasonality and habitat availability. The evolution of Nearctic shorebird migration in the interior of South America appears to have been influenced by seasonal cycles of precipitation and the effects on habitat availability.
Resumen.--Se registraron 20 especies de playeros durante 47 censos a lo largo de los m�rgenes del r�o Paraguay en la bah�a de Asunci�n, Paraguay, desde 1987 hasta 1989. La mayor�a de migrantes ne�rticos (15 especies) alcanzaron n�meros m�s altos durante el oto�o boreal que durante la primavera, presumiblamente a causa de las inundaciones de la cuenca del r�o Paraguay durante la primavera y el verano; los residentes neotropicales (cinco especies) alcanzaron n�meros m�s altos durante diciembre-marzo. La abundancia de la mayor�a de playeros, especialmente los neotropicales, fue correlacionada negativamente con el nivel de agua, una medida inversa de disponibilidad de h�bitat. La variaci�n interanual en abundancia pareci� estar relacionada con las condiciones hidrol�gicas locales. Cada especie explot� un cierto h�bitat en una manera diferente, proveyendo evidencia de la partici�n de h�bitat. Los tama�os de las bandadas intraespec�ficas de la mayor�a de las especies fueron correlacionados con abundancia y, por inferencia, estacionalidad y disponibilidad de h�bitat. La evoluci�n de migraci�n por los playeros ne�rticos en el interior de Sudam�rica parece haber afectado por ciclos estacionales de precipitaci�n y los afectos sobre la disponibilidad de h�bitat. |
