Baseline characterization of the diet and stable isotope signatures of bears that consume natural foods in central Japan

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Measures of δ13C and δ15N in tissues of Asiatic black bears (Ursus thibetanus) can be useful in helping researchers identify nuisance bears and in determining whether a specific bear might be consuming anthropogenic food such as garbage and corn. However, the δ13C and δ15N values of native foods vary across the bear’s range. The purposes of this study were to characterize the stable isotope ratios of bear tissues and potential non-anthropogenic food items and compare that characterization to other studies and an independent analysis of bear food habits. We collected hair from bears in the Ashio–Nikko Mountains (ANM) that, based on capture location and radiotelemetry data, were consuming non-anthropogenic food. We found that the δ13C ratios of bear hair from the ANM were significantly higher than those of bears sampled in another area in central Japan where bears were also eating native food. Bears in the ANM consumed large amounts of ants in summer. Ants in this part of the ANM have relatively higher δ13C value than ants from other areas. M iscanthus sinensis, a C4 plant with a high δ13C value close to that of corn , is abundant in parts of the ANM. We also found that the δ13C of herbivorous insects that may not be consumed by bears also had high δ13C content. From these analyses, the δ13C in bear hair in the ANM was high because bears consume ants in summer and because ants in turn may consume herbivorous insects that feed on C4 plants. Past studies indicate that high δ13C values in bear hair may be used to identify nuisance individuals that damage corn on farms. However, our results showed that bears consuming natural foods may also have high δ13C levels in some regions. Thus, identification of nuisance bears based on isotope data should account for variation in the isotopic signatures of non-anthropogenic food items and should identify and use locally appropriate isotopic end members.