Evolution of the chaffinch, Fringilla coelebs, on the Atlantic Islands

Chaflinches have differentiated within the last million years on the Canary Islands and the Azores. All island populations differ more from mainland relatives than from each other. The characteristics of island birds are large body size, short wings, long legs and beaks, and blue dorsal colour. Beak depth and width have increased on the Azores but not on the Canaries. As a consequence the Azores chaffinch has evolved more in the direction of the Canary Island F. teydea than have Canary Island chaflinches. Character displacement may have occurred on the Canaries. Most of the evolutionary shifts are not predicted from a knowledge of clinal variation on the mainland. Populations have differentiated more on the Canaries than on die Azores, but are less variable regardless of whether ecologically restricted (by teydea) or not. Similarly, within the Azores archipelago the most differentiated populations are die least variable. On the Azores, but not on the Canaries, differentiation increases with isolation, whereas wimin-population variation decreases with isolation and increases with elevation. A model for diese patterns is proposed in terms of gene flow between populations, which reduces differentiation but enhances variation, and directional selection and random genetic processes which have the opposite effects.