Removing Wolf Packs Reduces Depredations
by Cat Urbigkit, Pinedale Online!
March 18, 2016
In contrast to a highly publicized (and highly criticized) December 2014 paper by a group of researchers at the Washington State University asserting that lethal control of wolves results in increased depredations on livestock in a larger area the following year, a new paper by wolf managers in the Northern Rocky Mountains found that "full pack removal was the most effective management response to reduce future livestock depredations in a local area." Researchers associated with the new paper suggested that depredation management is most appropriately studied at the wolf pack-level, or local scale.
The new paper, "Effects of Wolf Removal on Livestock Depredation Recurrence and Wolf Recovery in Montana, Idaho, and Wyoming," was published in the Journal of Wildlife Management by authors associated with Montana Fish, Wildlife and Parks, U.S. Fish and Wildlife Service, University of Montana, and USDA Wildlife Services.
The researchers studied nearly 1,000 depredations by 156 known wolf packs in the tri-state area, comparing the management response to depredations: no removal, partial pack removal, and full pack removal. The median time between recurrent depredations was 19 days following no removal, 64 days following partial pack removal, and 730 days following full pack removal.
"Compared to no removal, full pack removal reduced the occurrence of subsequent depredations by 79% over a span of 1,850 days (5 years), whereas partial pack removal reduced the occurrence of subsequent depredations by 29% over the same period," according to the paper.
The researchers found: "Partial pack removal was only slightly more effective in reducing depredation recurrence than no removal, and then only if it occurred within the first 7 days after the depredation. Partial pack removal resulted in a median of only 45 days additional time without depredations compared to no removal. However, caution should be used in generalizing the effects of partial pack removal. In this study, partial pack removals averaged 2.2 individuals, thus most of our data represented small removals. Partial pack removals were more effective the more wolves removed."
The researchers noted that wolf depredation on livestock is a learned behavior "and therefore may be difficult to stop if all individuals in a pack are involved." The social disruption caused to the pack associated with partial removal did not increase depredations by packs in the study.
"We found pack size was the most important wolf-related predictor of recurring depredations; therefore, managers should aim to reduce pack size as much as is practical to prevent future depredations following an initial depredation event," the researchers concluded, adding that reducing pack size can be achieved, at a lower agency cost, through public hunting. Montana’s wolf hunting season has resulted in a decrease of wolf pack size (from an average of 7 wolves/pack to 5 wolves/pack), which has been accompanied by a decrease in livestock depredations and agency wolf removals, while the overall wolf population has experienced little change.