Migration is a pattern of behavior in which animals travel from one habitat to another in search of food, better conditions, or reproductive needs. There are two important factors that make migration different from other types of animal movement: First, migration happens seasonally, and second, migration involves a return journey.

The migration cycle is often annual and thus closely linked with the cyclic pattern of the seasons. The migration of most birds and mammals and many of the fishes are on a yearly cycle. In many cases (e.g., salmon and eels), animals with a relatively long life span return to their place of birth in order to reproduce and eventually die.