Age- and Sex-Associated Differences in the Diet of the Asian Black Bear: Importance of Hard Mast and Sika Deer

In the context of reducing human-bear conflict, understanding potential foraging variation within a bear population yields insights into differences in foraging strategy according to an individual's sex and age. Stable isotope analyses reveal information regarding assimilated dietary components. To confirm the foraging variation of Asian black bears and assess its underlying factors, we conducted stable isotope analysis of hair samples. We constructed linear mixed-effect models to examine the effects of sex, age, and hard mast abundance on bear diet. Furthermore, we used stable isotope data on food resources to estimate bear diets from isotopic mixing models to evaluate differences in dietary components among age-sex classes. During the reproductive season, delta N-15 values were positively correlated with bear age, and dietary deer fraction was the highest for adult males. Our results also showed that during the hyperphagia season, bears were mostly dependent on hard mast, regardless of its abundance. However, delta N-15 values of bears were higher during poor mast years than when mast was plentiful, thus implying that bears consume increased proportions of deer and/or insects (e.g., Vespidae) in poor mast years. Our results indicate that feeding strategies in Asian black bears differ according to age-sex classes and seasons.