Data from: 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
inhabiting the Spanish sector of the Iberian Peninsula and estimated their
climate niche position by calculating the effects of ambient temperature,
insolation and precipitation on bird occurrence at a fine 10 x 10 km
spatial scale. 4. After controlling for the body size and the nocturnal
condition of species, and for phylogenetic and spatial effects, we found a
positive association between plumage reflectance and the functional
response of bird distribution to spring-summer ambient temperature and
insolation but not to precipitation. Thus, bird species preferentially
occupying the hotter and sunnier areas of Spain exhibit lighter plumage
pigmentation. A similar association between pigmentation and preferences
regarding precipitation in geographical distribution was not found. 5. Our
findings suggest that darker birds are limited to occupying environments
with high temperatures, unveiling a constraint in endotherms imposed by
their pigmentation phenotype.