The origin of bird migration. Migratory patt erns in Catalonia

Migratory behaviour involving regular movements between different areas is very common in the animal kingdom. In birds, migration between the breeding and wintering grounds normally takes place in an annual cycle. This article presents the various hypotheses regarding the origin of migratory behaviour, the factors that are probably involved in it and the alterations linked to climate change. The appearance of migratory behaviour in birds could be related to factors such as the increase in resources in the breeding ranges in spring or other ecological factors such as predation, parasitism and competition, all of which diminish at increasing latitude. Regarding climate change, during the Last Glacial Maximum the ice coverage in the Northern Hemisphere affected mostly the breeding areas, possibly resulting in a decrease in the migratory distance. In current times, however, climate change presents a new threat for migratory species, which need to quickly adapt their migratory strategies in both time and space in order to survive under the changing conditions. The article also presents results from three general patterns of migration in Europe: the broad-front migration of flapping birds such as the quail to many coastal areas in the Balearic Sea in spring; the preferential directions of birds coming mainly from the north-east that pass through or winter in Catalonia; and the altitudinal migrations of the black redstart, the wallcreeper and the white-winged snowfinch, which also maintains metapopulations between the Alps and the Pyrenees.