Cattle depredation risk by gray wolves on grazing allotments in Washington

Abstract

Livestock depredation was a primary factor in wolf extirpation from most of the conterminous United States by the 1930s. Through reintroductions and natural dispersals, gray wolves (Canis lupus) have recolonized portions of their former range. Livestock grazing occurs on federal lands in the western United States, including 31% of wolf-occupied areas in Idaho, Montana, and Washington. We investigated characteristics of cattle (Bos taurus) grazing allotments (n = 70) in Idaho (2004–2008), Montana (1991–2008), and Washington (2008–2016) to predict cattle depredation risk on grazing allotments in current and probable wolf-occupied areas of Washington (n = 162). Depredation probability and the predicted number of cattle depredated increased for allotments with higher cattle and wolf abundance. Top models accurately predicted 38% (n = 8) of allotments with verified cattle depredations as ≥61% depredation probability. Assuming pack sizes of five or ten wolves, 10% (n = 16) and 15% (n = 24) of cattle grazing allotments in Washington were forecasted at ≥61% depredation probability, respectively. This preliminary study identified areas in which wildlife and rangeland management agencies can focus proactive depredation prevention measures. However, additional fine-scale data (e.g., GPS locations of depredation locations and wolf core areas, animal husbandry practices, actual number of cattle by age class) are needed to improve model performance and further evaluate cattle depredation risk by wolves on grazing allotments in Washington.