Abstract: Altitudinal migration is defined as the seasonal movement of birds from high level breeding haunts to lower levels during the winter. Data is given on the movements of selected species and it is shown in some cases that the migrants maintain a territory in their winter quarters. Evidence from ringed birds shows that species undertaking altitudinal migration do so year after year proving that the phenomenon is not merely a dispersal by young birds. There are no known forests where the whole population moves to lower levels. The significance of the migration is discussed and it is concluded that its evolution was related to vicissitudes of the pseistocene climate. At the present time it is probably important in maintaining gene flow between populations in montane forest, a highly fragmented and, in many areas, a vanishing habitat.