Most birds that swoop over ocean waters have one thing in common: dark wings. Now scientists think they know why. Dark feathers absorb more heat, which improves flight efficiency, allowing these birds to fly faster and longer than those with lighter-colored wings.
Researchers had investigated this mystery before. Whereas most scientists have focused on the typical functions of colors, such as how birds’ feathers can help them with mating, hiding from predators, or finding food, others have looked at how darker feathers might improve flight efficiency. These experiments, which included 3D printed wings, led to conflicting results, however.
So in the new study, researchers tried to better replicate the real world. Evolutionary biologists at Ghent University examined museum specimens of 324 species of seabirds, including ospreys, northern gannets, and great black-backed gulls. When they compared the wing coloration of these birds with what is known about their flight performance, they found that darker-winged birds tended to be better flyers.
The team then stuffed two real northern gannet wings with cotton and propped them up in a wind tunnel. One wing was white with black tips, the other was dark all over. The scientists altered wind speeds and wing position; they also simulated various Sun intensities with infrared light bulbs. The dark wing heated up more, as expected. But this hotter wing was also more efficient, experiencing up to 20% less drag than the lighter wing, the team reports this week in the Journal of the Royal Society Interface.
Unlike birds that live on land, seabirds fly for long periods of time in extreme heat and wind, notes co-author Matthew Shawkey, also at Ghent University. Similar adaptions may also be used by other species that fly long distances, such as butterflies, he says.
The findings of this “great project” could also be used to improve drone technology and the aviation industry, says Mostafa Hassanalian, a mechanical engineer and biomimicry researcher at the New Mexico Institute of Mining and Technology who was not involved with the work. “This is actually going to be the future of science, where the combination of two different areas like this helps us to come up with new studies.”