Population-Level Assimilated Dietary Responses of Black Bears to Baiting

Wildlife feeding through intentional or unintentional practices can result in increased human-wildlife conflict, disease transmission, population growth, and altered behavior. We quantified how spatial and temporal variation in black bear (Ursus americanus) bait availability within home ranges influenced black bear diet composition as mediated by sex and age. We tested carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes in hair samples from hunter-harvested bears during pre-baiting (about 1 May-9 August) and baiting (about 10 August-26 October) periods in Michigan, USA, 2017-2021 and used isotopic mixing models to estimate how diet varied between sexes and with spatially-varying bait distribution. We used linear models to determine whether intrinsic (i.e., sex, age) and extrinsic (i.e., region, bait quantity and distribution) factors were correlated with δ¹³C and δ¹⁵N enrichment of black bear hair during pre-baiting and baiting periods while controlling for corn agriculture, distance from waste accumulation sites, and human population density. Proportion of anthropogenic food in black bear diet was greater during the baiting period, especially for female black bears, but bait density did not influence black bear diet composition. Black bear hair from the Northern Lower Peninsula was more enriched in δ¹³C as compared to the Upper Peninsula and had the greatest δ¹³C and δ¹⁵N enrichment at about 10 years of age. Bait density and distribution did not influence δ¹³C or δ¹⁵N enrichment in black bear hair, potentially due to bait availability. Our results demonstrate that anthropogenic food from intentional and non-intentional sources contributes substantially to black bear diet in Michigan, which may affect body condition, behavior, reproduction, and abundance.