A comprehensive theory for the evolution, control and adaptability of avian migration

Theories about the evolution of migratory behaviour in birds have recently been grouped in eight categories (Rappole 1995). Common to all of them is the idea that migration originated in ancestral sedentary populations by some kind of 'behavioural jump'. These are difficult to explain, especially under the assumption that migration has evolved several or many times independently. Recent experimental studies undertaken to illuminate the genetics of bird migration and the potential and speed of the associated microevolutionary processes have led to another view - a simple yet comprehensive theory. Its central concept is (obligate) partial migration, which is extremely widespread at higher latitudes, possibly also in the tropics, and seems to have evolved very early or might even have been inherited from pre-avian ancestors. Partial migration provides a behavioural turntable from which exclusive migratoriness and sedentariness can easily and rapidly be reached (or left) through selection and related microevolutionary processes. The fact that all important migratory features are directly genetically controlled, that migratoriness and amount of migratory activity are based on a common genetic mechanism, and that migratory syndromes exist, probably all greatly facilitate microevolutionary changes from migratoriness to sedentariness and vice versa.