都市公園におけるニホンリス（Sciurus lis）の再導入事業の検証

抄録

From February, 1984, to June, 1986, twenty-one Japanese squirrels (Sciurus lis; 11 males, 10 females) were reintroduced into Shinjuku Gyoen (58 ha) in central Tokyo. However, squirrels were not observed since December 1987. This report summarizes the issues related to the reintroduction of squirrels based on the results of this project and the ecological knowledge on squirrels produced by subsequent research. Approximately 36 ha of the forest were used by squirrels. The main foods were walnut and Lithocarpus edulis acorn from feeding stands, seeds of Pinus thunbergii, P. densiflora, exotic conifer trees, and Castnopsis cuspidata var. sieboldii acorn. Three carcasses of squirrels predated by Felis catus were confirmed, and Corvus spp. chased the squirrels. The squirrels did not settle because the forest area of the site was not sufficient considering the home range of squirrels; there was no habitat to move to close by, and dependence on acorns as forage was overestimated. Issues: 1) forest area of the site corresponding to the home range size of squirrels, 2) conservation of forests with diverse tree species, and 3) management of feral cats and crows as predators.