The distribution of the Malayan Night Heron Gorsachius melanolophus in the Yaeyama and Miyako Islands, southern Japan

抄録

The Malayan Night Heron Gorsachius melanolophus is a threatened species that inhabits the Yaeyama Island group in the extreme southwest of the Ryukyu Archipelago, southern Japan. The species' distribution in Japan, which has been poorly known, was surveyed on the basis of sound and sight records, and interviews. The species was confirmed to occur on Ishigaki, Iriomote, Kuroshima, Kohama, Taketomi, Hateruma, Yonaguni, Miyako, Kurima, and Tarama islands. This range is wider than expected and records were independent of the area of islands. The past underestimation of the species' range was likely to have been the result of a lack of research effort and the unremarkable ecology and morphology of the species. The population density was found to be higher on Iriomote Is., covered with abundant forest, than on Ishigaki Is. with more degraded forests. Despite the wider than previously thought range, its range is still not very extensive in Japan; furthermore, increasing predators and introduced competitors may well endanger the population in the near future.