Looking at a quarter century's worth of data collected by the U.S. Fish and Wildlife Service's annual wolf reports, scientists were able to track how many wolves were killed legally. By pairing this information with livestock statistics from the U.S. Department of Agriculture, the researchers could examine the link between culling wolves and the rate at which these predators attacked livestock.
Washington State University biologist and study author Rob Wielgus wasn't sure if killing wolves would help to save livestock. Last year, Wielgus and his colleagues had found that culling cougars resulted in more, not fewer, livestock deaths - evidence that killing these animals was senseless.
Killing wolves, it turns out, is also senseless, as it fails to protect livestock to a surprising degree. With the death of a single wolf, cattle and sheep deaths bump up the next year by about 4 percent. Kill 20 wolves, and livestock are twice as likely to be killed. It's not that wolves are bound by some sort of canine revenge code; instead, as Wielgus and WSU environmental scientist Kaylie Peebles reported Wednesday in the journal PLOS ONE, the death of a wolf can fragment a pack, causing smaller groups of wolves to disperse. If the immigrant wolves settle and have pups near livestock, they're more apt to attack the farm animals, rather than straying away to chase down elk or deer.