Bird migration: a novel theory for the evolution, the control and the adaptability of bird migration

The migratory behaviour of many bird species is currently changing, evident ly in connection with global warming; in general there is a shift towards s edentariness. Because experimental studies indicate that all crucial aspect s of migration are under direct genetic control, it is unlikely that the ob served changes result from phenotypic plasticity. Equally improbable is the assumption of more numerous mutations in the same direction. Instead, the cause may well be rapid processes of selection and microevolution, which ar e demonstrable in the field and experimentally reproducible. An ideal initi al situation for selection processes is partial migration. Such birds' gene tic predisposition for both migration and nonmigration amounts to a kind of turntable, from which migrants, residents and partial migrants with variou s proportions of migratory and nonmigratory individuals can be selected. Pa rtial migration is not only the most common Life form among birds, but is a widespread type of behaviour that developed early in the evolution of plan ts and animals. The new bird migration theory postulates that birds either evolved partial migration very early or inherited it from avian ancestors, like other characteristics of migration such as compasses and fat depositio n. In any case, birds thus possess a fundamental control mechanism which, d epending on the environmental situation, permits the rapid emergence of phe notypic migrants or residents or transitional mixed populations comprising various combinations of migrant and resident individuals. This simple new t heory allows us to dispense with the previous concept that migratory birds arose polyphyletically from nonmigrants by mutational "behavioural jumps"-a concept that cannot explain, for instance, the currently increased shift a way from migratory behaviour.