Migratory birds are specially adapted to find their way over extreme distances that represent remarkable tests of endurance. Now, researchers of the Max Planck Institute for Ornithology in Seewiesen and colleagues have discovered an unexpected way that migratory birds keep their cool during such arduous journeys: lighter-colored feathers.
"We found across nearly all species of birds, migratory species tend to be lighter colored than non-migratory species,” said Kaspar Delhey of the Max Planck Institute for Ornithology, Seewiesen, Germany. “We think that lighter plumage coloration is selected in migratory species because it reduces the risk of overheating when exposed to sunshine. Lighter surfaces absorb less heat than darker ones, as anybody wearing dark clothes on a sunny day can attest! This would be particularly important for long-distance migrants that undertake extensive flights during which they cannot stop to rest in the shade.”
Delhey and colleagues had been studying the effects of climate on bird coloration. Their earlier studies showed that, in general, lighter colored birds are found where temperatures are high and there is little shade. Presumably that’s at least in part because the birds’ lighter plumage helps to keep them cooler in the hot sun. Around that same time, the researchers came across studies by others showing that some birds fly at much higher altitudes during the day compared to at night.