Scientists have found that in most birds the urge to migrate is caused by changes in day length. However, some birds like crossbills and waxwings migrate in some years but not others. Apparently, these birds get the urge to migrate only when the weather is exceptionally cold or food is scarce. For many years, biologists have been trying to figure out how birds are able to find their way during migration. Different birds seem to use different methods, and even an individual bird may use different methods under different weather conditions or in different areas.
Many birds use the moon, sun, and stars to find their way.
Scientists have found that birds will try to migrate in the wrong direction in a planetarium if the pattern of sun, stars, and moon in the planetarium sky are changed. Many birds follow mountain ranges, sea coasts, and rivers during migration. This map shows some of the bird migration routes from Alaska to other parts of the world. Semipalmated sandpiper, blackpoll warbler 2. Sandhill crane, peregrine falcon, some dabbling ducks 3.