Present condition of the avifauna of Mukojima, Ogasawara archipelago, following the eradication of feral goats

摘要

Mukojima is an uninhabited island in the northern part of the Ogasawara archipelago. The island's, vegetation was drastically disturbed by feral goats Capra aegagrus hircus after 1945. The change in the avifauna resulting from this habitat disturbance has previously been described. Japanese Bush Warbler Cettia diphone and Bonin Honeyeater Apalopteron familiarebecame locally extinct. In recent years, the goats have been exterminated and the vegetation is now recovering. To clarify the current stituaion of the avifauna on Mukojima, we counted bird numbers along two routes from March to June, 2007. We also recorded the vegetation along the routes. Many Japanese White-eye Zosterops japonicus (an introduced species) were observed in the forest, and several Blue Rock Thrush Monticola solitarius were observed in open areas. These were the only two species observed throughout our study period; both were confirmed to be breeding. Other native land birds, Common Buzzard Buteo buteo, Brown-eared Bulbul Hypsipetes amaurotis, White's Trush Zoothera dauma, Japanese Bush Warbler Cettia diphone were less abundant, with only a few individuals of each species observed for short periods. In the future, such vistors to Mukojima may increase as the vegetation recovers. Japanese White-eye will contribute to the recovery of the vegetation as they are both seed dispersers and pollinators, although they may compete with indigenous species for food.