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Data from: Colourful urban birds: Urban-tolerant birds have more elaborate colours, more blue and less brown

Ibáñez-Álamo, Juan Diego1; Delhey, Kaspar2; Izquierdo, Lucía1; Valcu, Mihai2; Kempenaers, Bart2

Published Jan 20, 2025 on Dryad. https://doi.org/10.5061/dryad.jq2bvq8jg

Data files

Jan 20, 2025 version files 1.06 MB

Abstract

Urbanization, one of the most extreme and rapidly-expanding human-induced landscape changes, imposes multiple challenges to wildlife. Studies in urban ecology have explored how urbanization affects organisms. However, still little is known about the relationship between urbanization and animal coloration, even though colours fulfil key functions such as camouflage, signalling, and thermoregulation. We use a global bird database on urban tolerance and combine it with quantitative colour estimates to test whether urban-tolerant species differ in colour from less urban-tolerant ones. Our interspecific comparative analyses revealed that urban-tolerant birds are more likely to have blue, dark grey and black colours and less likely to have brown or yellow colours. However, after statistically accounting for phylogenetic relatedness, only the effects of blue and brown colours remained significant. Overall, urban-tolerant species have more elaborated colours, but we found no association between urbanization and sexual dichromatism. Additionally, we performed assemblage-level analyses to test whether urban assemblages are less-colour diverse, a key prediction of the urban colour homogenization hypothesis. Our results did not support this hypothesis: after accounting for species richness, urban bird communities were more, rather than less, colour diverse. Thus, our results suggest that plumage colours are part of an urban-associated syndrome. Cities may select against species with colours that provide camouflage in natural settings, such as brown, because these colours are no longer cryptic in the urban environment. Increased colour elaboration in urban settings may also be related to reduced risk of predation by visual predators. These effects were stronger in females, although sexual dichromatism was not significantly correlated with urban-tolerance. Our findings clearly show that species that are prone to live in urban environments differ in colour from those that avoid cities.