Biogeography, origin and evolution of avifauna in the Comoro Islands

The Comoro Islands appear to have been colonised by land birds in succesive stages. An initial, ancient wave resulted in 9 endemic species, of African (or possibly Asian) origin. A second wave, represented by 4 species and 22 more endemic subspecies, originated from Madagascar. Other, more recent arrivals of nesting birds are still undistinguishable from forms present in Madagascar (5), Africa (4), or both areas (8). Interpretation of these data is complicated, however, because definitive isolation mag. have been more likely for colonisers from Africa than from Madagascar due to prevailing wind direction and the presence of stepping-stones (additional intermediate islands) in the Pleistocene. Unfortunately, few fossils are available. Multiple colonisations of a single taxon from one source have been demonstrated. Grand Comoro, the highest, largest, and westernmost in the archipelago, along with Moheli, a satellite one fifth its size, form a centre of speciation. Mayotte in the east is another, smaller speciation centre, which is surprising considering its proximity to Madagascar. The central island, Anjouan, is poor in endemics, and shows affinities with Aldabra, sharing with it several species of direct Malagasy origin not found elsewhere in the archipelago. Some species present on Aldabra and the granitic Seychelles may have arrived as colonists from the Comoros. These diverse patterns caution against using generalized explanations for the colonisation of Indian Ocean islands by land birds.