Migration Migration is a seasonal movement from one area to another - usually a breeding and a nonbreeding area. Migration evolved in response to environments that change with the seasons. Migration allows birds to take advantage of productive seasons and avoid unproductive seasons.
Most migrant birds spend only two to four months of the year on their nesting grounds.
The majority of the year is spent elsewhere. Not all birds migrate. Some find the resources they need throughout the year, others switch to different food sources as the seasons change, and a few become inactive during lean times. Prior to migration, birds build up body fat to burn as fuel during their journeys. The exact ways in which birds use these cues is still largely a mystery.