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Why birds migrate to the Arctic

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Photo courtesy of Laura McKinnon

(Read caption) White-rumpled sandpiper (Calidris fuscicollis) chicks, Bylot Island, Nunavut, Canada.

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Why don’t migratory birds just stay home? Why do they travel tens of thousands of miles — from the tip of South America to the Arctic, for example — and back every year?

By any measure, these trips are long, arduous, and costly. Migratory birds risk storms, predators, and fatigue, to say nothing of humans with guns. And the farther north they nest, the more it costs metabolically just to be there.

Scientists have long assumed that birds make these trips because summering grounds at the top of the world offers some advantage. Whatever the costs are, in other words, the migratory birds must be more than compensated by some quality unique to the Arctic.

Indeed, with constant sunlight fueling plant growth, the Arctic summer is notable for its explosion of life. And scientists have long thought that this abundance of resources — as well as a relative lack of competition for them — has something to do with enticing birds to (evolve to) migrate there.

The extreme environment of the far north also has fewer parasites. Traveling to environs with fewer parasites might be well worth the price of the voyage. A large parasite load can take quite a toll.

Now, a new study in the journal Science emphasizes another reason the long voyage may be worth it for birds: fewer predators.

Titled “Lower Predation Risk for Migratory Birds at High Latitudes," the study finds that, the farther north birds go in the Arctic, the lower the risk of predation. Fewer predators mean that vulnerable young have greater chance of survival. Even accounting for the huge energy cost of the long voyage, having young in the Arctic improves reproductive success.

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