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J R Soc Interface. 2019 Jul 26;16(156):20190032. doi: 10.1098/rsif.2019.0032. Epub 2019 Jul 24.

Hot wings: thermal impacts of wing coloration on surface temperature during bird flight.

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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.


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.


bird flight; colour; radiative heating; thermography; wind tunnel; wing surface temperature

[Available on 2020-07-01]

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