Five Incredible Ways Birds Change Their Bodies for Spring and Fall Migration

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Five Incredible Ways Birds Change Their Bodies for Spring and Fall Migration - Audubon

To power perilous journeys, birds undergo extreme feats like doubling their body weight and rearranging or even consuming their internal organs.

It’s tempting to compare bird migration to marathon running. In both, participants prepare intensely and undergo an extreme test of endurance. But the similarities stop there. Though marathon runners push the human body to its limits—during the 26.2-mile race, core temperatures spike to 102 degrees Fahrenheit and the heart pumps three to four times more blood than usual—birds radically change their bodies and their metabolism for the main event. In just weeks or months, they undergo physical transformation unmatched by human gains from years of training. To fly vast distances between breeding and wintering grounds, birds can shrink their internal organs, rapidly gain and burn through fat stores, barely sleep, and more.

These are incredible abilities, but they come with tradeoffs. The energy required to fly hundreds or thousands of miles in a short span leaves birds with little room for error during migration, and vulnerable to natural and human-caused threats. In North America alone, an estimated 2.6 billion birds disappear between fall and spring migration every year. Researchers pin many of these losses on migration, when birds must survive storms and cold snaps, navigate skyscrapers and other buildings, avoid predators, and successfully forage for food or else fail to complete their journeys.
 
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