The Declining Distribution of the Okinawa Rail Gallirallus okinawae.

Abstract

The distribution of the Okinawa Rail Gallirallus okinawae was studied, using the voice play back method, at 296 sites in 1996-1999 and at 564 sites in 2000-2001, in the northern part of Okinawa Island. The results were plotted on a 1.25km×0.925km map grid. The presence of Okinawa Rails was confirmed at 49 out of 95 grid intersections (51.6%) during 1996-1999 and at 116 out of 255 grid intersections (45.5%) in 2000-2001. These results were compared with similar research undertaken by the Environmental Agency in 1985-1986. This comparison indicates that the border of the species' range has shifted north by about 10km over the past 15 years, resulting in a 25% decrease in the range of this species. Between 2 October 2000 and 30 March 2001 Okinawa Prefectural Govern- ment carried out controls of the introduced mongoose Herpestes javanicus in northern Okinawa Island using approximately 800 traps located at a total of 2,470 sites. A total of 303 mongoose were caught, mainly in the southern area from which Okinawa Rails have disappeared in recent years. The result of rail population mapping and of mongoose trapping strongly imply that the mongoose has caused the range contraction of the Okinawa Rail. We believe that urgent conservation measures are required in order to prevent this species from becoming extinct.