Migration
A regular seasonal movement of the whole or part of a population with an outward journey followed, some time later, by a return journey. Although most migratory movements involve travelling between breeding grounds and winter quarters at some distance, there are other types, including altitudinal migration and moult migration. An irruption or weather movement, because of its irregular nature, is not a true migration. The British Isles are well placed on a major flyway and there is a well developed bird observatory network for studying migration.From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver