Both techniques have provided new ideas on how and where birds migrate. Birds migrate for a variety of reasons. They might need to escape approaching cold weather or look for more food sources. But knowning when to migrate and where to go is a complex issue. Even now all the answers are not known.
Most scientist agree that the changing day length is a huge cue for migration.
As days get shorter, migrating birds become anxious and restless. Pretty soon they are like a wind-up toy wound too tight. Usually, a changing weather pattern such as a cold front will be the final trigger that sends them on there way. Once they start flying, birds use many special and unique ways to navigate to their wintering grounds. Indigo bunting use the stars to find their way while other use the sun to steer.