CONTRASTS IN THE SONGS OF TWO SYMPATRIC

species with broader niches to exclude a greater number of specialists. VAN VALEN (1965) examined bill sizes in six species of birds from island and from mainland populations. In five of these, birds of the island population had fewer competitors and morphological variation was greater there than on the mainland. In the sixth case, that of the Canary islands chaffinch Fringilla coelebs tintillon, morphological variation was reduced compared with...