Dietary specialization depending on ecological context and sexual differences in Asiatic black bears

The food habits of the Asiatic black bear ( Ursus thibetanus ) are well studied, but there is a little evidence of dietary specialization—that is, when individuals use a narrower set of resources compared to the population as a whole. To examine the dietary composition at the individual level, seasonal patterns of dietary specialization, and sex-based dietary differences in Asiatic black bears, we attached Global Positioning System (GPS) collars to 15 Asiatic black bears and collected their scats in Nagano Prefecture, Japan from 2017 to 2018. Our results showed that the dietary composition differed among individuals, although seasonal changes in dietary composition were observed at the population level. Dietary specialization was high in summer (resources less abundant) and low in spring and autumn (resources more abundant), indicating a relationship with general food abundance and the dietary diversity of bears. In spring, all bears consumed green vegetation and/or seed of Fagaceae family from previous autumn; in early- and late- summer, dietary composition, such as green vegetation, insects, and fruits, greatly differed among individuals. In autumn, most bears heavily depended on seeds of Fagaceae which is high-quality food for bears. Although we did not find statistical differences between sexes in terms of dietary specialization and diversity, we found variations in the timing of feeding on the Fagaceae family, being earlier in females compared with males. We also found considerable variation in dietary composition within sexes, suggesting that dietary specialization depends on multiple factors besides food abundance, food diversity, and sex.