Ecotropicos

Download full PDF

Abstract: Communal roosting sites are important for understanding social interactions and population dynamics of gregarious animals. While roosting behavior has been well studied in North American blackbirds (Icteridae), less is known about Neotropical colonial species, particularly outside breeding seasons. This study aims to characterize a roosting site of Crested Oropendolas (Psarocolius decumanus) during the non-breeding season in northern Venezuela. We recorded the abundance, sex ratios, and arrival times of oropendola flocks to the roosting site, as well as other species roosting nearby. Seven flocks making up to 287 Crested Oropendolas arrived in the evening, with a sex ratio of 3.5 females per male, contrasting with previous breeding season observations of male:female ratios (1:6 to 1:8). We also documented the presence of several Giant Cowbirds (Molothrus oryzivorus), an oropendola brood parasite. Since colonies count with less than ten individuals on average, our observations suggest that multiple nesting colonies use the same roost, which makes these sites central to understanding oropendolas’ social structure and population processes. Future research is needed to explore seasonal variation in the abundance and composition of roosts and their role in shaping intrasexual competition and/or dispersal patterns in oropendolas and other Neotropical gregarious species.