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.1. 动物色素的演化源自多种适应性功能。以动物体内最为常见的色素——黑色素（melanins）所介导的色素沉着为例，其核心功能为抵御紫外线辐射。然而，色素沉着同时会影响动物体表吸收太阳辐射并获取热量的能力，对于体温较高且恒定的恒温动物（endotherms）而言，这可能构成热约束。 2. 由于深色相较于浅色可吸收更多辐射，带有深色色素沉着的恒温动物在高环境温度下的生理表现或受限制，因此难以占据炎热生境。尽管色素沉着对变温动物（ectotherms，尤其是爬行类）热生态位的影响已成为多项研究的关注焦点，但针对恒温动物的相关探讨仍属空白。 3. 本研究对栖息于伊比利亚半岛西班牙辖区内的96种鸟类的黑色素介导的色素沉着表型表达量开展了精准量化，并以10×10km的精细空间尺度，通过分析环境温度、日射量与降水量对鸟类出现概率的影响，估算了各物种的气候生态位位置。 4. 在控制物种体型、夜行性特征，以及系统发育（phylogenetic）效应与空间效应（spatial effects）后，研究发现羽毛反射率（plumage reflectance）与鸟类分布对春夏季节环境温度和日射量的功能响应呈正相关，但与降水量无显著关联。换言之，优先栖息于西班牙境内高温高日照区域的鸟类，其羽毛色素沉着更浅。未发现色素沉着与物种地理分布对降水量的偏好存在类似关联。 5. 本研究结果表明，体色更深的鸟类难以占据高温生境，揭示了色素沉着表型对恒温动物所施加的热约束。