Evaluating the importance of breeding sites for rare seabirds in Hachijo-Kojima, Izu Islands ―Natural History Research Association of the Izu Islands―

<p>Hachijo-Kojima is the only island free of both weasels and snakes and retains the typical food web of the Izu Islands. Since the island became evacuated in 1969, an increase of feral goats and damage to vegetation through intensive browsing became apparent. Extermination of feral goat was implemented and successfully completed by 2017. The black-footed albatross began breeding and by 2022 the breeding pairs exceeded 100. On the other hand, the adjacent small island, Kojima, has been a breeding ground for small rare seabirds such as the crested murrelet, while slope erosion and collapse of the island narrowed the possible nesting sites which may cause disappearance of their breeding colonies. Therefore, while using monitoring of black-footed albatross as a basis, we surveyed birds on Hachijo-Kojima using sound loggers. As a result, 17 forest bird species and 3 seabird species were confirmed to inhabit the island, but small rare seabirds could not be discovered. Rodent species that exert predation pressure on birds and landsnails were surveyed, and we confirmed the presence of high densities of rats in a wide area from the coast to the top of the mountain. Predation traces were found on seven species of land snails, and were discussed as an indicator for monitoring rat population. We discussed several proposed measures to see if it would be possible to reduce rat population throughout the Hachijo-Kojima in the future.</p>