Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Comparing artificial ground nest predation pressure and predator composition in mongoose-infested and non-mongoose-infested areas of northern Okinawa Island.

Abstract

The Small Indian Mongoose Herpestes auropunctatus (hereafter mongoose), an invasive alien species, has a devastating effect on populations of Okinawa Rail Gallirallus okinawae and Okinawa Robin Luscinia komadori namiyei, species endemic to the Yambaru forest of northern Okinawa Island. In this study, we conducted artificial ground nest predation experiments in two forest sites in northern Okinawa Island to clarify the effects of predation pressure and predator composition. The first site was infested with mongooses while the second site not. Nest predation rates were high at both sites, and there was no statistical difference between them. At the mongoose-infested site, the artificial nests were preyed upon by Large-billed Crow Corvus macrorhynchos, mongoose and Rattus spp. At the non-mongoose-infested site, artificial nests were preyed upon by Okinawa Rail, Large-billed Crow, Wild Boar Sus scrofa and Rattus spp. In order to restore the forest ecosystem of the mongoose-infested area and to aid the conservation of at-risk endemic bird species, it is necessary to eliminate the mongoose from this area, and to properly manage the population of the Large-billed Crow, which is thought to have increased in the area as a consequence of human activity, and other invasive alien species such as Rattus spp. At the non-mongoose-infested site, the Okinawa Rail was the predominant predator of artificial ground nests. We suggest that the Okinawa Rail has not only evolved flightlessness in the safe, low-predator island ecosystem of Okinawa Island but also to exploit a vacant niche usually exploited by mammalian carnivore species.