The term "birdbrain" sounds like an insult until you learn a few things about migrating birds. Arctic terns, for example, somehow steer an 11,000-mile course each autumn from their breeding grounds north of the Arctic Circle to the antipodes of the Southern Hemisphere. They locate favorite stopovers on the Bay of Fundy, fly three days nonstop over the blank face of the northern Atlantic, negotiate the west coast of Africa, and home in on their habitual winter haunts on the Antarctic pack ice. Then, come spring, they head back north again—along a different route up the eastern coast of South and North America.
"These birds are making the longest journeys among animals on earth," says ecologist Thomas Alerstam of Lund University in Sweden.
Whether migrating or homing, birds are unsurpassed as navigators. Yet scientists still haven't found the mechanisms in bird brains that account for the birds' skill. The cues birds rely on to orient themselves aren't simple or obvious. People, for example, often use geographical cues—landmarks—to navigate. But homing pigeons can get back to their lofts from unfamiliar territory even if they're anesthetized on the outbound trip. They can find their way even while wearing frosted contact lenses that blur anything farther than a few yards beyond their beaks.
