Migratory birds travel over extreme distances. This represents remarkable tests of endurance. It was discovered that there is one unexpected factor that favors their performance. It is the color of their feathers. Lighter feathers help migratory birds. The study was published in the journal ‘Current Biology’.
Avoiding the heat
“Migratory birds tend to be lighter than non-migratory birds.” Kaspar Delhey, from the Max Planck Institute for Ornithology, says in a statement. He works in Seewiesen (Germany). “We think it is to reduce overheating when they are exposed to the sun.”
“Lighter surfaces absorb less heat than darker ones. This is important for long-distance migrants who make long flights. During them they can’t stop to rest in the shade,” he explains.
Delhey and his colleagues had studied the effects of climate on bird coloration. He found that the lightest-colored birds are where there are high temperatures and little shade.
He surmises that the birds’ lighter plumage helps them stay cooler in the sun. Other studies found that many birds fly higher during the day than at night.
“Flying high is probably costly. Therefore, this behavior must have an explanation. Flying higher involves flying where it is colder. This compensates for the heat absorbed by the plumage when the sun shines.”
If so, they realized that another way to reduce the risk of overheating would be to absorb less solar radiation in the first place. This raised the question of whether migratory species with lighter feathers have evolved.
The results show that bird species get lighter and lighter as they migrate more. They observed the same pattern in large and small birds. And the same was true for waterfowl and land birds. It is clear that lighter feathers help migratory birds.
His team will continue to explore the factors that explain the evolution in plumage color. They hope to identify how migratory species cope with the challenges of thermoregulation.