A recent study out of the scientific journal PLOS One reports that killing a wolf that preys on sheep or cattle is not be the best strategy to protect the livestock. In fact, it might even increase the likelihood that the remaining wolves in the pack will feed on these animals.
The findings note that when a single wolf is killed, the chances of livestock getting killed increased the following year in that state by 5 to 6 percent for cattle and 4 percent for sheep. The chances of livestock attacks rose higher with each additional wolf killed. The trend doesn’t flip until more than a quarter of wolves are killed in one year.
Lead author of the study, Rob Wielgus, a Washington State University ecologist, isn’t sure why livestock deaths increase with the number of wolves killed, but he suspects it’s tied to changes in pack behavior. A male and female breeding pair lead a pack, so if one of these wolves is killed, the pack will break up. The result is more breeding pairs, and thus an increase in the wolf population. It’s only when enough wolves are killed to overwhelm their ability to keep up through reproduction that the number of livestock lost decreases.
These observations match those made in and around Yellowstone National Park, where wolves are protected from hunters. Around the park, packs are large, complex webs of relationships, different from groups elsewhere, where packs tend to be just a breeding pair and pups.
"It's a bit of a catch-22," Wielgus said, noting that while killing a wolf might be necessary in the short term, in the long term it’s counterproductive and unsustainable. On one hand, wolves are killed and livestock losses go up. On the other hand, if wolves continue to be killed to stop livestock losses, then they end up back on the endangered species list. When wolf killing rates fall below 25 percent per year, then the number of livestock killed increases.
"You can reduce them now, but you can only reduce them so far, and when you stop that heavy harvest, now you're at maximum livestock depredation," Wielgus adds.
These findings add fuel to an already heated debate. Executive Director of the Idaho Wool Growers Association Stan Boyd said his group works with members to help them deter wolves from killing livestock without killing them, but he still sees guns as a necessary tool.
“Wolves get into livestock, we kill the wolves. And that works well,” Boyd said. “The professor can say whatever he wants. We're not going to just let wolves run wild.”