Department of Biology, Evolution and Optics of Nanostructures Group, University of Ghent, K. L. Ledeganckstraat 35, 9000 Ghent, Belgium.
Department of Soil Management, Research Group Soil Degradation and Conservation, University of Ghent, Coupure Links 653, 9000 Ghent, Belgium.
J R Soc Interface. 2019 Jul 26;16(156):20190032. doi: 10.1098/rsif.2019.0032. Epub 2019 Jul 24.
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 up 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 coloration and muscle temperature both play important roles in modulating wing surface temperature and therefore potentially flight efficiency.
最近关于鸟类飞行的研究表明，较热的翅膀表面可以减少摩擦阻力，从而提高飞行效率（升阻比）。较暗的翅膀在太阳辐射下可能比浅色翅膀升温更快。我们使用三种方法来测试颜色对翅膀表面温度的影响。首先，我们根据反射率测量来模拟表面温度。其次，我们使用热成像技术对活体鱼鹰（Pandion haliaetus）进行了研究，以检查随着太阳辐射的增加表面温度的变化。第三，我们在风洞中对不同颜色的翅膀进行了实验加热，并在实际飞行速度下测量了翅膀表面温度。即使在模拟飞行条件下，深色翅膀也始终比浅色翅膀升温更快。在带有黑色尖端的白色翅膀中，产生的温度差会导致朝向较暗的翅膀尖端的对流，从而增加升力。此外，翼展上温暖的肌肉和较冷的飞行羽毛之间的温度差可以延迟机翼上方的气流分离，从而提高飞行效率。总之，这些结果表明，翅膀颜色和肌肉温度都在调节翅膀表面温度从而潜在地影响飞行效率方面发挥着重要作用。
