Urban environments create a unique suite of conditions, leading to changes in animal behavior, morphology, phenology or physiology. Condition-dependent traits such as the carotenoid-based coloration offer a unique opportunity to assess the impacts of urbanization on organisms because they reflect the nutrition, health or other resource-based attributes of their bearers and they play an essential role in intra- and inter-sex interactions. To determine if and how the carotenoid-based coloration of male house finches (Haemorhous mexicanus) varies along a gradient of urbanization, we quantified the plumage coloration of more than 1200 individuals in urban, suburban, rural and desert habitats over the course of 17 months. We also examined for the first time the preference of females for male plumage coloration across the urban-rural gradient, to test if and how female preferences varied relative to the range of plumage coloration displayed by males in their local population. We found that carotenoid-based coloration decreased along the gradient of urbanization, suggesting that the enzyme-driven metabolic conversion of dietary carotenoids into red carotenoids used to color plumage is sensitive to urban stressors. The stronger negative effect of urbanization on carotenoid-based plumage colouration during breeding than during molt and winter suggests that urbanization affects colour fading rate, maybe through modifications of feather-degrading bacterial load. Finally, we have shown that urbanization influences female mate choice behavior, suggesting that female color preferences may track the variation in male coloration across the gradient of urbanization.

Giraudeau et al. 2018 Behavioral Ecology Field DataIncludes data on carotenoid-based plumage hue for three separate regions (crown, breast, rump), body mass, site of capture, and urbanization indices for each individual bird.Giraudeau et al. 2018 Behavioral Ecology Data.csvGiraudeau et al. 2018 Behavioral Ecology Mate Choice DataData file includes, for each female, the capture site, observation and experiment number, observation date, and time near each male and the respective male's identity and plumage hue.Mate_Choice_Exps.csv