Prey switching occurs when a generalist predator kills disproportionately more of an abundant prey species and correspondingly spares a rarer species. Although this behaviour is a classic stabilizing mechanism in food web models, little is known about its operation in free-living systems which often include dangerous prey species that resist predation. We used long-term (1995–2015) data from a large mammal system in northern Yellowstone National Park, USA, to understand how prey preference of a wild, generalist predator (Canis lupus) responds to a shift in prey species evenness involving rising numbers of dangerous prey (Bison bison) and dropping numbers of relatively safer prey (Cervus elaphus).