TERMS,STUDIES AND EXPERIMENTS ON THE PROBLEMS OF BIRD DISPERSION*

A terminology of the dispersion of birds, and of the ways in which it comes about, is proposed and explained. An examination of recoveries of ringed female Pied Flycatchers Ficedula hypoleuca show that many first breed a considerable distance from their birthplace, in contrast to the situation in the Blue Tit Parus caeruleus and Nuthatch Sitta europaea. The degree of such dispersion in these species, and presumably therefore the gene flow, is inversely correlated with the number of geographical races they contain. Results of experiments designed to investigate the types of dispersion mechanism occurring in F. hypoleuca indicate that both “dispersal” and “spacing” occur in birds of all ages, and that they are usually not oriented, but that the spacing of older birds which have not been constantly faithful to place usually leads to a previously known place.