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 t he idea that migration originated in ancestral sedentary populations by som e kind of 'behavioural jump'. These are difficult to explain, especially un der the assumption that migration has evolved several or many times indepen dently. Recent experimental studies undertaken to illuminate the genetics o f bird migration and the potential and speed of the associated microevoluti onary processes have led to another view - a simple yet comprehensive theor y. 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 an cestors. Partial migration provides a behavioural turntable from which excl usive 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 g enetic mechanism, and that migratory syndromes exist, probably all greatly facilitate microevolutionary changes from migratoriness to sedentariness an d vice versa.