Resource Use and Population Densities of Prairie and Yellow Warblers in an Area of Recent Contact—the Florida Keys

摘要

Historically, the Florida Prairie Warbler (Dendroica discolor paludicola) and the Cuban Yellow Warbler (D. petechia gundlachi) were not in contact during the breeding season, but they now occur together in extreme south Florida. We studied the resource use and population ecology of these species in black mangrove habitats in the Florida Keys. Most prey items obtained by warblers were taken from leaves by gleaning or hovering. These methods of prey acquisition accounted for between 60% and 70% of all foraging observations for male and female warblers of each species, suggesting a large overlap in diet. There were no significant differences in the foraging substrates (P > 0.98) or foraging methods (P > 0.86) used by Prairie and Yellow warblers. Yellow Warblers tended to forage higher than did Prairie Warblers, particularly in areas of tall (> 2.5 m) mangroves, but there was considerable overlap and the differences may not be biologically significant. Male warblers also tended to forage higher in mangroves than did female warblers. Point counts show an inverse relationship between the average number of Prairie Warblers and the average number of Yellow Warblers detected in different study sites, suggesting density compensation by the Prairie Warbler as the Yellow Warbler colonizes Florida mangrove habitats. However, this pattern could be the result of habitat preferences. Prairie and Yellow Warblers occur in about equal numbers in habitats dominated by tall mangroves, but Prairie Warblers were much more common than Yellow Warblers in habitats dominated by shorter mangroves (< 2.5 m). Our study suggests large amounts of resource overlap between Prairie and Yellow Warblers, but future studies would be useful in determining if this is a long-term trend or if Prairie and Yellow Warblers will begin to diverge in foraging behavior after a longer period of sympatry.%Históricamente, la Reinita galana de la Florida (Dendroica discolor paludicola) y el Canario (reinita) de mangle de Cuba (D. petechia gundlachi) no entraban en contacto durante la temporada reproductiva, pero al presente ocupan las mismas áreas en el extremo sur de la Florida. Hemos estudiado el uso de recursos y la ecología poblacional de ambas especies en habitáculos de mangle negro en los Cayos de la Florida. La mayoría del alimento capturado por las reinitas fue obtenido de la superficie de las hojas a través de técnicas de rebusqueo o de vuelo suspendido. Estos métodos de adquisición de presa representaron un 60% a 70% de todas las observaciones alimenticias realizadas por ambos sexos en cada especie de reinita. Lo anterior sugiere un gran solapamiento en la dieta de ambas especies. Por otro lado, no se detectaron diferencias significativas entre los substratos alimenticios (P > 0.98) o entre los métodos alimenticios (P > 0.86) utilizados por la Reinita galana y el Canario de mangle. Los Canarios de mangle tienden a alimentarse a una mayor elevación que las Reinitas galana, particularmente en áreas de mangle alto (> 2.5 m), pero se encontró un solapamiento considerable y las diferencias puede que no sean biológicamente significativas. Las reinitas macho también tienden a alimentarse a una mayor elevación en los mangles que las hembras. Los censos de punto realizados muestran una relación inversa entre el número promedio de Reinitas galanas y de Canarios de mangle detectados en diferentes áreas de estudio, sugi-riésendose una compensación de densidad por parte de la Reinita galana a medida que el Canario de mangle coloniza los habitáculos de mangle en la Florida. Sin embargo, este patrón puede ser el resultado de preferencias de habitáculo.