Risk of bear-inflicted human injury in Yellowstone National Park

Yellowstone National Park, USA, is a popular tourist destination with sympatric populations of grizzly bears (Ursus arctos) and American black bears (U. americanus). It receives >4 million recreational visits annually, and bear–human interactions are common. Many visitors are concerned about the risks of recreating in bear habitats, and wildlife managers are interested in knowing the risk of bear attack to inform safety messaging, reduce the frequency of bear attacks, and/or to address concerns regarding reintroduction of grizzly bears. To address those objectives, we analyzed 45 years (1979–2023) of recreational use statistics and bear attack data to estimate the risk of injury by bears while visitors are engaged in different recreational activities, including front-country recreation, overnight camping in roadside campgrounds and backcountry campsites, and backcountry hiking and horseback riding on overnight trips. We used generalized linear models to estimate the effects of these different types of use and of bear species on the rate of bear-inflicted human injury in the park. We found overall rates of injury were low (∼1/3.6 million visits caused by grizzlies and ∼1/23.2 million visits caused by black bears) and have decreased concurrently with increasing park visitation. Risk of injury varied by activity type and bear species involved. Users of vehicle-accessible campgrounds had a ∼98% lower rate of bear-inflicted injury than those in backcountry campsites. There was a marginally significant (P H 0.088) effect of species on the rate of injury to overnight users (stock riders and backpackers combined) with the rate of injury caused by grizzly bears being ∼5× that of black bears. When considering all use types combined, grizzly bears caused a ∼6.5× higher rate of injury than black bears did. Backcountry hikers are most at risk of injury from grizzly bears. Educational efforts should focus on activity types most at risk and emphasize science-based strategies for reducing surprise encounters.