Temporal changes in the population density and diet of brown bears in eastern Hokkaido, Japan

抄録

In eastern Hokkaido, Japan, occurrences of human-brown bear (Ursus arctos yesoensis) conflict have increased during the last decade. Locals speculate that these conflicts have been caused by an increase in the bear population and/or changes in bear ecology, although no evidence is available to support either hypothesis. We compared scat densities and the diets of bears for the years 1978 and 1998–2000 in Urahoro, eastern Hokkaido. The scat density in 2000 tended to be lower than in 1978, suggesting that bear density has not increased over the last two decades. In 1978, herbaceous plants were the dominant early and late summer foods of bears. Berries, including Rubus spp. and Actinidia kolomicta, were dominant late summer foods. In contrast, sika deer (Cervus nippon yesoensis) meat appeared frequently in bear scats in all seasons in 1998–2000, at a much higher percentage than in 1978. Crops, including sugar beet and corn, also increased in early and late summer. These results suggest that the diet of bears has changed over the last two decades, and that bears have become more dependent on deer and on crops. We conclude that the increase in human-bear conflicts is not because of an increase in the bear population, but because of the increased dependence of bears on deer and crops as food sources.