Data from: Hot wings: thermal impacts of wing colouration on surface temperature during bird flight.

Recent studies on bird flight propose that hotter wing surfaces reduce skin friction drag, thereby improving flight efficiency (lift-to-drag ratio). Darker wings may in turn heat faster under solar radiation than lighter wings. We used three methods to test the impact of colour on wing surface temperature. First, we modelled surface temperature based on reflectance measurements. Second, we used thermal imaging on live ospreys (Pandion haliaetus) to examine surface temperature changes with increasing solar irradiance. Third, we experimentally heated differently coloured wings in a wind tunnel and measured wing surface temperature at realistic flight speeds. Even under simulated flight conditions, darker wings consistently became hotter than pale wings. In white wings with black tips, the temperature differential produced convective currents towards the darker wing tips that could lead to an increase in lift. Additionally, a temperature differential between wing-spanning warm muscles and colder flight feathers could delay the flow separation above the wing, increasing flight efficiency. Together, these results suggest that wing colouration and muscle temperature both play important roles in modulating wing surface temperature, and therefore potentially flight efficiency.

近期针对鸟类飞行的研究提出，翼面温度越高，皮肤摩擦阻力（skin friction drag）越低，进而提升飞行效率，即升阻比（lift-to-drag ratio）。相较浅色翼面，深色翼面在太阳辐射下升温速率更快。本研究采用三种方法探究翼面颜色对翼面温度的影响：其一，基于反射率测量结果构建翼面温度模型；其二，对活体鹗（Pandion haliaetus）开展热成像（thermal imaging）观测，分析翼面温度随太阳辐照度（solar irradiance）升高的变化规律；其三，在风洞（wind tunnel）内对不同颜色的翼面开展加热实验，并在模拟真实飞行的速度下测量翼面温度。即便在模拟飞行工况下，深色翼面的温度仍始终高于浅色翼面。对于带有黑色翼尖的白色翼面而言，温度差会形成朝向深色翼尖的对流气流（convective currents），这可能提升升力水平。此外，贯穿翼部的温热肌肉与温度更低的飞羽之间形成的温度差，可延缓翼面上方的气流分离（flow separation），进而提升飞行效率。综合上述研究结果可知，翼面着色与肌肉温度均对翼面温度调控具有重要作用，进而可能对飞行效率产生影响。