The changing anthropogenic diets of American black bears over the past century in Yosemite National Park



We used carbon (δ13C) and nitrogen (δ15N) stable isotopes derived from the tissues of American black bears (Ursus americanus) to estimate the proportion of human-derived foodstuffs and food waste (“human foods”) in the diets of human food-conditioned bears over the past century in Yosemite National Park, located in central–eastern California. Our goal was to understand how the foraging ecology of bears responded to changing management strategies. We found that the proportion of human foods increased in bear diets when park personnel and visitors fed bears intentionally in 1923–1971, remained relatively high and constant after artificial feeding areas were closed, and declined drastically in 1999–2007, following a $500 000 annual government appropriation used to mitigate human–bear conflicts in the park. This reduction in the amount of human foods in bear diets suggests that Yosemite managers have been successful in reducing the availability of human foods to bears. Yosemite bears currently consume human foods in the same proportion as they did in 1915–1919. This result indicates a notable management achievement in the park, considering that thousands of people visited Yosemite annually in the early 1900s while about four million people visit each year today.