Light as a feather

Revealed: A beautiful connection between birds’ appearances and their behavior

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The color of birds’ feathers reveals a lot about them: Their gender, their habitat, their diet...

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But there are other factors that play into feathers, too.

Like migration.

This month, researchers use data from almost 10,000 bird species to tease out a relationship between migration and feathers — specifically, how pale a bird’s feathers tended to be.

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First, the team separated the data by sex — males tend to be brighter in color than females.

They also controlled for other factors that may affect feather coloration.

Then they gave each species’ feathers a lightness ranking from 0-100, with 0 being the darkest in shade, and 100 being the palest in hue.

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For all birds, feather color variation consistently reflects their migration habits.

The further a bird migrates, the lighter its feathers are, on average.

Current Biology

What’s the deal?

Some migratory birds fly higher in the sky than others, the researchers note. Like Icarus, the Sun’s heat can beat down on their backs the higher they go. But unlike Icarus, birds’ wings don’t melt — and lighter feathers may help regulate their body temperature at these higher altitudes.

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“We think that lighter plumage coloration is selected in migratory species because it reduces the risk of overheating when exposed to sunshine.”

Kaspar Delhey, study co-author

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The authors say their work has implications for how climate change might affect the darkness or lightness of birds’ feathers.

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Birds are already changing their bodies to adapt to warming temperatures and changing habitats.

In the Amazon rainforest, for example, birds are shrinking.

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Evolving lighter plumage could give them an advantage — but more research is needed to know how much they would benefit or whether this is already taking place.