A city of oropendolas: Characterization of nesting colonies of Crested Oropendola (Psarocolius decumanus) in Caracas, Venezuela

Abstract

Cities are constant-expanding novel ecosystems that present multiple pressures for birds, but they can offer opportunities for generalist taxa with traits that ease their establishment. The Crested Oropendola (Psarocolius decumanus) is a Neotropical blackbird that nests colonially in different environments, from mature lowland forest edges to cultivated clearings, including other human-altered ecosystems. Here, we aim to characterize Crested Oropendola colonies in Caracas, Venezuela, a city where these birds have become more common in recent years. During 3 years (2016–2018), we recorded the number of complete nests per colony and tested for differences in colony size based on site characteristics and urban features. Additionally, we did multivariate ordinations (NMDS) to detect associations between such features and colony size, as well as spatial autocorrelation tests for size and change in the number of nests across years. By 2018, we recorded 45 colonies with 317 nests in Caracas (mean = 7), the largest quantity of oropendola colonies found in any locality until now. We report for the first time evidence of solitary nesting behavior and show that colonies placed in multiple trees were fairly common (29%). Colony size was not related to most nesting site features, with the exception of presence of nearby roads. Colonies close to roads showed significantly larger sizes than colonies far from them, potentially due to their isolation from predators. The mean distance between colonies was 1.1 km and we detected a slight negative spatial autocorrelation in nest change among neighboring colonies. We pinpoint differences in colony size and nesting patterns among Psarocolius species, likely related to different degrees of polygyny. Finally, we discuss the potential relationship of coloniality and isolated nesting sites, among other factors, in facilitating the establishment of this species in the city. The Crested Oropendola population in Caracas offers an opportunity to investigate reproductive and social aspects of the species and the evolution of colonial icterids.