Non-lethal tools for reducing livestock depredation, such as livestock guardian dogs (LGDs; Canis familiaris), have been widely adopted by domestic sheep (Ovis aries) producers in the United States and reduce the need for lethal management of livestock predators. The use of LGDs reduces the number of livestock killed by carnivores, although the mechanism by which LGDs reduce depredation is unclear. For instance, little is known about how carnivore populations respond to LGDs. Presumably, grazing sheep act as an attractant to carnivores, but it is unclear whether the addition of LGDs ultimately attracts or displaces livestock predators. To test the effect of sheep grazed with LGDs on the small-scale occupancy of livestock predators, we deployed trail cameras in grazed areas of Idaho, Montana, Oregon, Washington, and Wyoming during the 2014-2016 grazing seasons. Photos were collected from 206 camera locations over 6,215 trap days. Data were used to model the probability of co-occurrence for sheep bands grazed with LGDs and large carnivores. Here we focus on the effect of LGDs and sheep on the occupancy of some of the largest livestock predators, which are also the focus of many conservation efforts - wolves (Canis lupus) and grizzly bears (Ursus arctos).
Results/Conclusions
Model ranking indicates that the presence of sheep grazed with LGDs does not affect the probability of occupancy for either wolves or grizzly bears. None of the top co-occurrence models (delta AICc < 2.00) includes separate occupancy probabilities for grizzly bears when sheep and LGDs are present. Similarly, the top four models of co-occurrence with wolves indicate no difference in occupancy probability when sheep and LGDs are present. One lower-ranked wolf model (delta AICc = 1.97, model weight = 0.069) suggests that occupancy probability for wolves is slightly lower when sheep and LGDs are present (Ψ = 0.063, 95% CI = 0.019-0.193) than when they are not (Ψ = 0.199, 95% CI = 0.074-0.436), although confidence intervals overlap considerably. These results suggest that the presence of LGDs and sheep does not attract or displace wolves and grizzly bears on the landscape. They also suggest that if LGDs reduce livestock depredation it is through some mechanism other than causing large carnivores to avoid areas with grazing sheep.