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in biology, an animal that leaves its natural habitat, migrating beyond the boundaries of its accustomed area of distribution. The migration of such animals is frequently massive and is usually related to mass reproduction, which results in a shortage of food and, therefore, in the departure of animals from their natural habitat. Examples of emigrants are lemmings, squirrels, nutcrackers, Pallas’s sandgrouse, various species of swarming locusts, and sometimes the steppe lemming (Lagurus lagurus), as well as butterflies and their caterpillars and dragonflies.
Emigrants perish in large numbers while moving. Some drown when crossing rivers, and many fall victim to predators. They frequently fail to find a suitable new habitat and die. There have been some cases in which animals’ areas of distribution have been expanded as a result of migration. Examples in the 20th century include the population of Kamchatka by squirrels in the 1920’s and the population of the Antilles Islands by the buff-backed heron (Bubulcus ibis) in the 1930’s.