Galván Ismael, Palacios Daniel, Negro Juan José
Department of Evolutionary Ecology, Doñana Biological Station - CSIC, 41092 Sevilla, Spain.
Department of Zoology, University of Córdoba, 14071 Córdoba, Spain.
Front Zool. 2017 Mar 1;14:15. doi: 10.1186/s12983-017-0201-5. eCollection 2017.
Dark pigments provide animals with several adaptive benefits such as protection against ultraviolet (UV) radiation and mechanical abrasion, but may also impose several constraints like a high absorbance of solar radiation. Endotherms, with relatively constant and high body temperatures, may be especially prone to thermoregulatory limitations if dark coloured and inhabiting hot environments. It is therefore expected that adaptations have specifically evolved because of these limitations. Bare, highly vascularised head skin may have evolved in birds with dark plumage from hot geographical regions because of favouring heat dissipation. Using the Northern bald ibis () as a model species, we measured the surface temperature (T) of the head, the bill and the black feathered body of 11 birds along ambient temperatures (T) ranging from 21 to 42.5 °C employing thermal imaging.
While T of the bill and the feathered body was only slightly above T, head T was considerably higher, by up to 12 °C. Estimated values of heat loss followed similar variations. We also found that the red colour intensity of the head of ibises increased with head T, suggesting that birds are capable of controlling blood flow and the thermoregulatory function of the head.
These findings are consistent with the hypothesis that bare skin has evolved in dark pigmented birds inhabiting hot environments because of their ability to dissipate heat.
深色色素为动物提供了多种适应性优势，如抵御紫外线辐射和机械磨损，但也可能带来一些限制，比如对太阳辐射的高吸收率。恒温动物体温相对恒定且较高，如果体表颜色深且生活在炎热环境中，可能特别容易受到体温调节的限制。因此可以预期，由于这些限制，特定的适应性特征已经进化出来。裸露的、血管高度丰富的头部皮肤可能已经在来自炎热地理区域的深色羽毛鸟类中进化出来，因为它有利于散热。我们以北方秃鹳（）为模型物种，利用热成像技术，在21至42.5°C的环境温度范围内，测量了11只鸟的头部、喙部和黑色羽毛身体的表面温度（T）。
虽然喙部和羽毛身体的温度仅略高于环境温度，但头部温度要高得多，高达12°C。热损失的估计值也有类似的变化。我们还发现，秃鹳头部的红色强度随头部温度升高而增加，这表明鸟类能够控制头部的血流和体温调节功能。
这些发现与以下假设一致，即生活在炎热环境中的深色羽毛鸟类进化出裸露皮肤是因为它们具有散热能力。
