Migration is the cyclic or periodic travel of an animal as it returns eventually to its original place of departure.
Migration is often annual and is closely linked with the cyclic pattern of the seasons.
It is most evident among birds, which have a highly efficient means for traveling swiftly over long distances. The migration of most birds is a yearly cycle. Not all birds migrate. The more severe the climate of an area, the greater percentage of nesting birds migrate. Two-thirds of bird species found in the United States migrate, some only short distances to more southern states.