Migratory divideThe boundary between two adjacent population groups whose autumn migration takes them in different directions. The divide may or may not be marked by a physical feature such as a mountain range. For example, for most species breeding on the Siberian tundra there must be a zone west of which the population migrates south-westwards to winter in Europe and Africa and east of which there is a southerly or south-easterly movement to southern Asia, the East Indies and Australasia.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver