Colourful Urban Birds: Bird Species Successful in Urban Environments Have More Elaborate Colours and Less Brown

Rapidly expanding urbanisation presents significant challenges to wildlife. Consequently, many studies have investigated the impact of urbanisation on diverse organisms. However, despite the ecological relevance of animal colouration, its association with urbanisation remains poorly understood. Using a global database, we computed an index of urban success for 1287 bird species and quantified its association with estimates of plumage colour. Our analyses showed that birds that do well in urban environments are more likely to be blue, dark grey and black, and less likely to be brown or yellow. After considering phylogenetic relatedness, only the effects of yellow and brown remained significant. Species with high urban success also exhibit more elaborate colours, but not higher sexual dichromatism. We provide eco-evolutionary explanations for these results. Assemblage-level analyses did not support the urban colour homogenisation hypothesis: Urban bird communities were more colour-diverse after accounting for species richness. Our findings suggest that plumage colours are part of an urban-associated syndrome.