Ground use pattern by forest animals and vulnerability toward invasion by Herpestes javanicus to Yambaru, northern Okinawa Island, southern Japan

We examined the ground use pattern of forest animals inhabiting Yambaru (the northern part of Okinawa Island) together with their vulnerability toward the invasion of the Small Asian Mongoose in to the area. We conducted a camera trap survey for two years (total 15,742.4 camera-days) to assess the relative abundance of ground dwelling animals. Among the 8,444 photographs, taken, we found that 87.6% (7,400) were of birds, while the remaining 12.4% (1,044) were of mammals. Among the birds were several endangered species such as Gallirallus okinawae (4,308 shots), the most frequently detected species, Erithacus komadori (910 shots) and Sapheopipo noguchii (108 shots). In this study we found, that almost all forest bird species (with the exception of owls), including largely nocturnal species such as Scolapax spp. and Gorsachius goisagi, used the ground during the daytime. We also found that the relative abundance of the ground dwelling bird species varied with the season as well as the year. The frequency with which G. okinawae was photographed was significantly higher during their summer breeding season than in winter, while the reverse was true for wintering species such as Turdus spp. and Scolapax spp, and for other resident species such as Streptopelia orientalis and Columba janthina. The relative abundance of Turdus spp. differed significantly between the two winters of the study, largely affecting the year-by-year change in composition of the ground-dwelling species in Yambaru. Such a trend in relative abundance of the ground dwelling bird species was affected by various factors such as breeding activity, migration, and seasonal niche shift. The relative abundance of G. okinawae was significantly lower in mongoose infested areas. In Yambaru forest, many endangered bird species use the ground during the daytime for breeding, resting and wintering. Thus, the invasion of the area by a diurnal predator such as the mongoose creates a crucial problem for the whole bird community of the forest in Yambaru.