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migration




Long-distance mass movements made by animals of many different groups, both vertebrate and invertebrate, often at regular intervals. Generally animals move from a breeding area to a feeding place, returning as the breeding season approaches the following year. This is the pattern of animal movements of migratory birds and fishes. Migrations of this nature may be over great distances, up to 11,000 km (7,000 miles) in some birds. Navigation is extremely accurate: birds may return to the same nest site year after year; migratory fish return to the exact rivulet of their birth to spawn. In other cases, migration may follow cycles of food abundance: Wildebeests in east Africa follow in the wake of the rains grazing on the new grass; caribou in Canada show similar movements. Certain carnivore species may follow these migrations, others capitalize on a temporary abundance as the herds move through their ranges.


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