Partial migration in birds: experimental proof of polymorphism as a controlling system

Summary When, from a partially migratory population of blackcaps, migratory-active (a) and-inactive (i) individuals were bred, the a×a pairs produced more birds of the type a than the original population and the i×i pairs, and the latter also more birds of the type i than the original population. Thus the characters migratory and resident in the blackcap are inherited and polymorphism is now demonstrated as a controlling system for partial migration in birds.With support by the Deutsche Forschungsgemeinschaft.We thank the French embassy for arranging permission to collect experimental birds.