As autumn is upon us, the annual avian fall migration is well under way for birds that use North American flyways to move from northern summering grounds to southern wintering areas. Geese fly overhead in V formations as they move south and colorful migrating warblers stop in local parks to rest up before continuing their journeys. This massive movement of birds brings with it an opportunity to learn about the biology and geography of migration, with a bit of mathematics thrown in for good measure. But before learning about these elements of migration, it is a good idea to discuss why birds undertake this expedition in the first place, and how they are able to accomplish the feat.
Most birds and other animals migrate for one or more of three basic reasons.