A brown bear (Ursus arctos) intruded into Higashi-ku, Sapporo City, Hokkaido, Japan, on June 18, 2021, and it attacked four people and caused injury. To prevent similar accidents, it is important to clarify the reason of the intrusion. In this study, we examined feces and stomach contents of the bear captured after the accident and analyzed carbon and nitrogen stable isotope ratios of body tissues to estimate the feeding history of the bear. The isotope ratios of hairs indicated that the bear had been on plant-based diets the year before the capture from spring to summer in 2020, but it seems to have started consuming salmon from summer to autumn in 2020, returned to a plant-based diet in the spring of 2021, and then abruptly started consuming river fish in June just before the capture. The isotope ratio of liver and the observations of its feces and stomach contents also indicated that the bear consumed river fish just before the capture. There was no evidence that the bear was dependent on anthropogenic food in garbage or on agricultural products. The bear had probably fished in the Ishikari River and surrounding small rivers, and fed on plants in vegetation-rich areas for several weeks before the capture. For bears, urban greening and green corridors are beginning to serve as temporary habitats or as intrusion routes into cities. Appropriate anti-intrusion measures are required for these green areas to prevent citizens from encountering bears.
