Status of land birds on selected islands in the Ha'apai group, Kingdom of Tonga

Abstract

Based on fieldwork in 1995 and 1996, I assess the distribution, relative abundance, and habitat requirements of indigenous species of land birds on 13 islands in the Ha'apai Group, Kingdom of Tonga. Among the islands visited, primary forest still exists only on the large (46.6 km2), hi~h (558 m) volcanic island ofTofua. Vegetation on the 12 smaller (0.15-13.3 km ), lower (6-45 m) islands is dominated by a mosaic of active and abandoned agricultural plots, nearly all with an overstory of coconut trees. Because of cultivation practices, very little of this vegetation is reverting to secondary forest. Of the 15 resident species ofland birds that survive on these islands, nine are widespread and at least locally common within Ha'apai, although only four (Gallirallus philippensis, Ptilinopus porphyraceus, Halcyon chloris, Aplonis tabuensis) certainly or probably occur nowadays on all 13 islands. Three species (Gallicolumba stairii, Ptilinopus perousii, Clytorhynchus vitiensis) are extirpated or extremely rare on all islands surveyed except Tofua. Overall species richness and abundance of land birds are much greater on Tofua than on the other islands. This difference may be due more to the presence of primary forest on Tofua than to Tofua's greater area and elevation.