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How do birds prepare their bodies for flight?
Migrating is a major physical challenge. To get ready for the trip, birds can make huge changes to their bodies in a matter of days. Birds rely on fat to fuel flight, in contrast to humans, who burn a lot of carbohydrates and sugars during exercise. Some will double their body weight beforehand by gorging on berries, insects, or mollusks. Others pump up the size of their flight muscles, increase their metabolism, and even grow or shrink their digestive organs to pack on or shed weight.
In a study of Gray