Those Amazing Birds: Sun Seekers

摘要

Migrating birds use the sun's location and a built-in biological clock to know which way to fly. Checking a compass is probably the last thing birds do before migrating. They want to make sure they leave in the right direction, and it's easy for themto do because their compass is built in. Only a small number of species have been studied in detail, but we know birds have at least three different kinds of compasses: solar, stellar, and magnetic. Birds that migrate by day likely determine their direction from the sun. Birds that migrate by night utilize the stars. And many, if not all, of both groups probably utilize the earth's magnetic field as a back-up system.