The diverse colours of bird feathers are produced by both pigments and nanostructures, and can have substantial thermal consequences. This is because reflectance, transmittance and absorption of differently coloured tissues affect the heat loads acquired from solar radiation. Using reflectance measurements and heating experiments on sunbird museum specimens, we tested the hypothesis that colour and their colour producing mechanisms affect feather surface heating and the heat transferred to skin level. As predicted, we found that surface temperatures were strongly correlated with plumage reflectivity when exposed to a radiative heat source and, likewise, temperatures reached at skin level decreased with increasing reflectivity. Indeed, nanostructured melanin-based iridescent feathers (green, purple, blue) reflected less light and heated more than unstructured melanin-based colours (grey, brown, black), as well as olives, carotenoid-based colours (yellow, orange, red) and non-pigmented whites. We used optical and heat modelling to test if differences in nanostructuring of melanin, or the bulk melanin content itself, better explains the differences between melanin-based feathers. These models showed that the greater melanin content and, to a lesser extent, the shape of the melanosomes explain the greater photothermal absorption in iridescent feathers. Our results suggest that iridescence can increase heat loads, and potentially alter birds' thermal balance.

鸟类羽毛的多种颜色是由颜料和纳米结构产生的，并且会产生巨大的热效应。这是因为不同颜色组织的反射率、透射率和吸收率会影响从太阳辐射获得的热负荷。通过对太阳鸟博物馆标本的反射率测量和加热实验，我们测试了颜色及其颜色产生机制影响羽毛表面加热和传递到皮肤水平的热量的假设。正如预测的那样，我们发现，当暴露于辐射热源时，表面温度与羽毛反射率密切相关，同样，皮肤水平达到的温度随着反射率的增加而降低。事实上，与非结构化黑色素基颜色（灰色、棕色、黑色）以及橄榄色、类胡萝卜素基颜色（黄色、橙色、红色）相比，纳米结构黑色素基虹彩羽毛（绿色、紫色、蓝色）反射的光更少，受热更多。 ）和无色素的白色。我们使用光学和热模型来测试黑色素纳米结构的差异或大量黑色素含量本身是否可以更好地解释基于黑色素的羽毛之间的差异。这些模型表明，黑色素含量较高，以及在较小程度上，黑素体的形状解释了虹彩羽毛中较大的光热吸收。我们的结果表明虹彩可以增加热负荷，并可能改变鸟类的热平衡。