Dark pigmentation limits thermal niche position in birds

1. Animal pigmentation has evolved because of several adaptive functions. In the case of pigmentation produced by melanins, the most common pigments in animals, the main function is protection against UV radiation. However, pigmentation also affects animal surface's ability to absorb solar radiation and gain heat, which may represent a thermal constraint for endotherms due to their relatively high and constant body temperatures.
2. As darker colours absorb more radiation than lighter colours, dark-pigmented endotherm animals may exhibit limited performance under high ambient temperatures and thus be constrained at occupying hot environments. While the influence of pigmentation on the determination of the thermal niches of ectotherms, particularly reptiles, has been the focus of several studies, this remains an unexplored issue for endotherm animals.
3. Here we made a detailed quantification of the expression of pigmentation phenotypes produced by melanins in 96 species of birds inhabi...