Natural history and conservation biology of the tooth-billed pigeon (Didunculus strigirostris): a review

Abstract

Fears that the evolutionarily distinctive tooth-billed pigeon (Didunculus strigirostris), endemic to Samoa, is close to extinction have prompted initiatives based on incomplete information. The species was widely distributed in forests on Upolu and Savaii from sea level to indeterminate elevations linked to its main food trees, Dysoxylum maota and D. samoense. Its bill is adapted to feed on Dysoxylum fruits although first-year birds apparently cannot do so. It occupies the middle strata of forest but sometimes forages discreetly on the ground. Breeding activity spans March to November, mostly April to September. One nest was in a Ficus at 25 m; other reports suggest similar locations. Birds sing sporadically throughout this period, but their reclusive behaviour, general silence and immobility render detection, and hence population density assessment, difficult. Many, but not all, nineteenth-century writers thought the species was becoming extinct, their reports conceivably reflecting real fluctuations in numbers. From the 1980s, however, evidence mounted that hunting and habitat destruction were seriously impacting the estimated 3200 birds on Upolu and 4800 on Savaii. Two cyclones in 1990 and 1991 destroyed much habitat; by 2000 only some 2500 birds were estimated to survive, and by 2006, when a recovery plan was issued, only 500; the most recent searches suggest fewer than 50 on each main island. Apart from hunting and habitat loss, predation by introduced rats and perhaps cats may be a serious limiting factor in the present century. Preservation and restoration of forests, elimination of hunting and control of predators are all needed, backed by a program of targeted research to establish the distribution of key Dysoxylum food plants and hence elevation limits, to identify any remaining forest areas with high density of Dysoxylum, and to study in detail the ecology and behaviour of birds in any and all surviving populations.