Field survey toward island ecosystem recovery after the extermination of goats on Hachijo-kojima Island ―Natural History Research Association of the Izu Islands―

<p>Hachijo-kojima is an island, where no weasels and cats were introduced, and the unique food webs of the Izu Islands remain. After all the islanders left in 1969, abandoned goats had drastically increased in number and had damaged on the native vegetation. We proposed the extermination of the goats, and the Tokyo Metropolitan and Hachijo-jima local governments exterminated a total of 1137 goats from 2001 to 2007. The native vegetation has seemed to be recovered, yet the ecological survey has not been conducted. We have conducted plant and animal survey starting from 2018 in order to contribute to the conservation and management of the unique island ecosystems. In 2019, land shellfish and insects surveys were added. From the survey, rare plant species such as Okuboʼs orchid (Platanthera okuboi), Kakiran (Epipactis thunbergii), and Oshima Shusuran (Goodyera hachijoensis f. izuohsimensis) were found for the first time since the goat extermination. The Okada's five-lined skink, nearly endemic reptiles of the Izu Islands, has occurred in higher density than on the other islands. The skink possesses different form and behavior compared to the same species of the other islands. The black-footed albatross (Phoebastria nigripes), the near threatened birds species, had landed on the island in 2013. Its breeding activity had been monitored. In the breeding season of 2016-2017, 2 young were recorded. The breeding success rate has improved from 2016-2017 (7 young in 2017-2018 and 26 young in 2018-2019). Other rare bird species were also found such as Ijimaʼs willow warblers (Phylloscopus ijimae), Seven Island thrushes (Turdus celaenops), Styan's grasshopper warblers (Locustella pleskei), and Japanese wood pigeons (Columba janthina). The Japanese wood pigeon, quite common on this island, is the representative bird species of the Izu Islands.The surveys on the land snails and insects have just started. No much information has been gathered, but many endangered land snail species have been recorded. These snails are native to Hachijo-kojima Island, where many alien snails are found in Hachijo Main Island. These results suggest that Hachijo-kojima Island has kept unique ecosystems of the Izu Islands. It is suggested that further continuous monitoring is needed.</p>