Regularly occurring, oriented seasonal movements of individuals of many animal species. The term migration is used to refer to a diversity of animal movements, ranging from short-distance dispersal and one-way migration to round-trip migrations occurring on time scales from hours (the vertical movements of aquatic plankton) to years (the return of salmon to their natal streams following several years and thousands of miles of travel in the open sea). This article will concentrate on seasonal movements, usually between breeding and nonbreeding areas, that have clear directionality and are long-distance relative to the sizes and locomotory abilities of the species involved.