The colorfulness of bird plumage plays a crucial role in intraspecific (e.g., sexual display) and interspecific ecological interactions (e.g., camouflage and predation). Functional traits like diet, body size, and sexual dichromatism are among the primary predictors of plumage colorfulness in passerine (Passeriformes) birds. Consequently, passerine plumage colorfulness and functional traits associated with it (i.e., diet, body size, and sexual dichromatism) can affect the success of individuals in novel environments, such as urban settings. However, our understanding of the impact of urbanization on the functional traits of birds, especially in tropical regions, is limited. To address this gap, we analyzed whether urban environments serve as environmental filters for plumage colorfulness, diet, body size, and sexual dichromatism in passerine bird assemblages across the biomes of Brazil, the world's largest tropical country. Using generalized linear and generalized linear mixed models that incorporate bird checklists, functional traits, urbanization, biomes, and sampling effort, we show that urbanization increases the proportion of omnivores, the proportion of larger species, and average sexual dichromatism in bird assemblages. While the average colorfulness of bird assemblages did not change with increasing urbanization, a negative correlation between the presence of megacolorful birds (i.e., the 5% most colorful species) and urbanization was detected, particularly in biomes with high urban concentrations, such as the Atlantic Forest and the Caatinga. This suggests that urban environments can be unsuitable for the most colorful tropical bird species. Our study additionally shows that factors like body size, diet, and sexual dichromatism play a mediating role in the urban filtering process. Our analyses provide insights into how urban environments act as environmental filters and can help to better understand the consequences of urbanization for tropical biodiversity.
Keywords: Brazilian biomes; bird functional traits; citizen science; colorfulness; passerines; sexual dichromatism; tropical biodiversity; urban ecology.
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