Annually, millions of birds leave their southern wintering grounds in search of food and a place to raise a family. The biological urge that triggers migration causes birds to store up fat for the energy to make the trip. They battle exhaustion, predators, and storms to reach the breeding grounds. Once the young are fledged the remarkable trip is reversed. Not all birds migrate.
Some species are permanent residents and live and breed in the same region.
Some merely move about within a small area as food availability changes. Others migrate short distances. But some birds make migratory journeys that are nothing short of spectacular. The paths that migratory birds take often follow geographic features such as mountain ranges and river valleys. These paths may vary greatly from year to year and also by species.