Estimation of feeding history by measuring carbon and nitrogen stable isotope ratios in hair of Asiatic black bears

Abstract

To investigate feeding habits, carbon and nitrogen stable isotope ratios were measured in hair sampled from Asiatic black bears (Ursus thibetanus) inhabiting an alpine area, including the Northern Japanese Alps and the periphery of villages in Nagano Prefecture, in central Japan. Asiatic black bears in the Northern Japanese Alps are subject to little human influence, but in rural areas human encounters with bears seeking food in cornfields and garbage have become an issue that needs to be resolved. We investigated the feeding habits of bears by analyzing the isotopic changes along the entire length of hair samples. Rural bears, including nuisance bears, showed slightly higher δ15N and δ13C values than alpine bears, suggesting that rural nuisance bears may have greater access to anthropogenic food resources than their alpine counterparts. Hair samples were further examined by growth section analysis (GSA), in which sectioned samples from the root to the tip are used for isotopic analysis, to estimate feeding history during hair growth. Hairs of alpine bears exhibited low δ15N and δ13C values from the root to the tip, and the deviation was small. In contrast, hairs of rural bears, particularly of nuisance bears, showed large deviations in isotope values. One bear captured in a cornfield showed high δ13C values at its hair root. Another bear that thrived on garbage showed high δ15N and δ13C values at its hair root, similar to those of Japanese people. One captured bear, assumed to be part of nuisance activities, showed low δ15N and δ13C values from hair root to tip, suggesting that captured bears are not always the ones causing damage. By comparing and classifying GSA fluctuation patterns, we estimated the dependence of nuisance bears on human-related food sources. We expect these methods to provide relevant information for bear conservation and management programs.