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Before shorebirds take to the air on the East Asian Australasian Flyway, they fatten up to twice their normal weight. Only then do they have enough fuel for the 7,000 kilometre flight to China. They grow bigger hearts, and bulk up their flight muscles. They also shrink their guts to shed unnecessary weight, says Chris Hassell, shorebird ecologist of the Global Flyway Network.

Image: Bar-tailed Godwit, feeding for migration, New South Wales. Credit: Ann Jones