How is animal migration different from emigration, invasion, and range expansion?

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A herd of wildebeest, including calves, moves across a dusty savanna in Africa with scattered trees visible in the background. — Migration A herd of common wildebeest (*Connochaetes taurinus*) migrating across a dusty savanna in Africa. The animal is a keystone species (i.e., a species with a disproportionately large effect on its biological community) in plains and acacia savanna ecosystems from southeastern Africa to central Kenya.

In ethology, animal migration is defined as the regular, usually seasonal, movement of all or part of an animal population to and from a specific area. It is distinct from other forms of animal movement in the following ways:1

Emigration: Unlike migration, which typically involves a return journey, emigration refers to a change in location that is not necessarily followed by a return to the original area.1
Invasion: While migration is regular and cyclical, an invasion involves the appearance and subsequent disappearance of large numbers of animals at irregular times and locations.1
Range expansion: Migration is a cyclical movement within a population's existing framework, whereas range expansion serves to enlarge the overall distribution of a species, particularly its breeding area.1

Migration is often linked to seasonal patterns, with many species traveling horizontally or vertically to survive environmental changes or to return to their place of birth for reproduction.1