Investigating Cause-Specific Mortality of Sheep to Determine the Impacts of Carnivores on Domestic Livestock

Livestock and carnivores interact in ways that are considered conflict throughout the world. In the western United States, livestock are often grazed on public lands in close proximity to predators in their natural habitat, and can be killed as prey. Livestock losses to predators can threaten rancher’s livelihoods. Sheep and lambs are especially vulnerable to predators due to their small size and lack of defensive abilities. To reduce the impacts that predators have on livestock, it is important for ranchers and wildlife biologists to have an accurate understanding of how many livestock die and are killed by predators when grazing on public lands. To better understand how sheep and lambs are affected when grazing on public lands, we used 934 VHF-radio collars placed on lambs in seven different sheep herds and monitored them from April-September 2021 to determine causes of death. In our study, 51 collared lambs died. Of these, 28 were found to have been killed by predators and 12 died of other causes, but we could not determine a cause for 11 because the carcasses were too decomposed. Predators that were found to have killed lambs include coyotes (Canis latrans), cougars (Puma concolor), and bobcats (Lynx rufus). We found that the biggest factor in determining how many lambs died were differences in animal husbandry (i.e., how the ranch operates when taking care of the lambs) or from specialization by individual predators within an allotment. We did not find any relationship among the time of year, whether a lamb was male or female, or the location of the lambs with how many died by predators. These results can help ranchers better care for their sheep and biologists better manage the predators in the areas where sheep are grazing.