Bighorn sheep respond to mountain lions with temporally dynamic forage-risk tradeoffs

Prey exhibit context and species-specific strategies to manage forage-predation risk tradeoffs. Mountain sheep select rugged escape terrain to minimize predation, despite reduced forage in these areas. Although bighorn sheep are diurnal and mountain lions, their most impactful predators, are nocturnal, previous research has not investigated whether bighorn sheep use an adaptive, temporally dynamic strategy to manage forage-risk tradeoffs. We estimated temporal activity and resource selection of female bighorn sheep in the Pine Ridge and Wildcat Hills subpopulations in Nebraska that are sympatric with mountain lions at the easternmost extent of both species' distribution. Bighorn sheep were strongly diurnal, whereas mountain lions were nocturnal. Consistent with the risk allocation hypothesis, females responded to temporal variation in risk by strengthening antipredator behavior at night when mountain lions were active by strongly selecting escape terrain and avoiding areas with abundant forage. Conversely, they relaxed selection of escape terrain during the day, freeing them to increase selection of abundant forage during safer times. Mountain sheep are known to prioritize safety by using steep, rugged terrain at the expense of foraging opportunities. We identified a temporally dynamic strategy used by females to navigate forage-risk tradeoffs that should provide energetic benefits. Our results inform conservation by showing that females in the Pine Ridge subpopulation that has declined precipitously navigated forage-risk tradeoffs less effectively than females in the stable Wildcat Hills subpopulation, suggesting indirect effects of avoiding predation. We provide new insight into forage-risk strategies for a species that is declining across much of its historical range.