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

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.