Why Killing Wolves Might Not Save Livestock

New study fuels debate over how to reduce attacks on cows and sheep.
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The remains of wolves killed by wildlife officials hang over the side of a truck in Montana in 2004. These animals, which were not part of the Huckleberry Pack, were killed because they attacked cattle.


In late August, a government sharpshooter in a helicopter hovering above a wooded eastern Washington hillside killed the lead female wolf of the Huckleberry Pack. The aim was to end attacks by the wolf pack, which had killed more than two dozen sheep.

But in the long run, a shooting like this could just make matters worse. A new study has found that—paradoxically—killing a wolf can increase the risk that wolves will prey on livestock in the future.

The research, published today in the scientific journal PLOS One, flies in the face of the common idea that the swiftest and surest way to deal with wolves threatening livestock is by shooting the predators. It adds to a growing understanding of how humans influence the complex dynamics driving these pack animals, sometimes with unexpected consequences.

As wolves spread across the West, triggering more encounters with sheep and cattle, and as two states host wolf-hunting seasons, the new research also adds more fuel to an already heated political debate about how to deal with wolves.

"The livestock industry, they're not going to be happy with this," said Rob Wielgus, a Washington State University ecologist and the study's lead author.

Back From the Brink

Shooting wolves is a long-standing practice in the ranching world. It helped lead to the animal's eradication in the western United States in the 1930s. Since the wolf's reintroduction in the mid-1990s, government officials and ranchers have frequently reached for a gun to cope with livestock problems—killing more than 2,000 wolves by 2013.

In 2011, wolves were removed from federal protection under the Endangered Species Act in Idaho, Montana, and parts of Washington, Oregon, and Utah. (Wyoming got a similar stamp of approval in 2012, but a federal judge recently overturned that decision.) That has made it easier to shoot wolves—Idaho and Montana now even allow recreational hunting.

But there have never been any large-scale studies of whether killing wolves really helps protect livestock.

Enter Wielgus. He has a track record for turning conventional wisdom on its head when it comes to attempts to control predators. In 2008 he made news with research that found shooting cougars led to more attacks on livestock. When mature adults were killed, Wielgus said, less seasoned adolescents moved in and were more likely to prey on cows and sheep.

After wolves arrived in Washington in 2008, growing to 13 packs by 2013, Wielgus turned his attention to the newest carnivore on the block. He examined 25 years of data on killing of wolves and cases where wolves attacked cattle and sheep in Idaho, Montana, and Wyoming—the first states where wolves were reintroduced.

What the Data Say

Wielgus found that when a wolf was 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. With each additional wolf killed, the chance of livestock attacks rose further. The trend didn't reverse until more than a quarter of the wolves in the state were killed in a single year. Then livestock losses started to decline.

That level of wolf-killing happened several times even while wolves were federally protected, under rules that allowed shooting of wolves that threatened livestock. And it is happening now in Idaho and Montana. Last year, hunters killed 231 wolves in Montana and 356 in Idaho, helping to reduce the population to slightly more than 600 in each state. The Idaho legislature this year created a Wolf Depredation Control Board, a move critics say is aimed at pushing wolf numbers down to just above 150—a cutoff that could trigger renewed protection under the Endangered Species Act.

Wielgus isn't certain why more livestock die when smaller numbers of wolves are killed. But he suspects it's tied to changes in pack behavior. Packs are led by a male and female breeding pair. If one or both of those wolves is killed, the pack can break up, giving rise to several breeding pairs—and thus an uptick in the wolf population. Livestock losses decline only when enough wolves are killed to overwhelm their ability to keep up through reproduction.

The theory fits observations made in and around Yellowstone National Park. Wolf packs inside the park—where wolves aren't shot—are large and complex, with wolves of a variety of ages living together, said Doug Smith, a lead wolf researcher at Yellowstone. Wolf packs elsewhere tend to be just a breeding pair and pups.

For Wielgus, the upshot of his study is that while killing a wolf might sometimes be necessary, as a routine practice it's counterproductive and unsustainable. Either livestock losses go up or, if enough wolves are killed to reduce livestock deaths, wolf numbers eventually drop so low that wolves wind up back on the endangered species list. If the killing slows to less than 25 percent of the wolf population per year, his study suggests, depredation rates shoot back up.

"It's a bit of a catch-22," Wielgus said. "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."

Is There Another Way?

Reaction to the new study was split down predictable fault lines. Wolf conservationists pointed to it as evidence that shooting wolves to save livestock usually doesn't make sense. "You have this very archaic paradigm of kill first, ask questions later," said Suzanne Stone, senior northwest representative for the environmental group Defenders of Wildlife. Overall, people in the livestock industry are "still pretty rigid in their views that the only way to deal with predators is to kill them. And that's not true. It actually works against them."

Stone has run a program with sheep growers in one Idaho valley aimed at finding ways for sheep and wolves to coexist. The ranchers there resort to a number of tactics to protect roughly 30,000 sheep: monitoring wolves to avoid grazing the sheep near denning sites, using guard dogs, flashing bright lights to scare off wolves, stringing a wire hung with small strips of fabric around the flock at night, and increasing the number of people herding the animals.

Stone said the program is cheaper than dispatching a gunman in a helicopter. Fewer than 30 sheep have been lost to wolves in seven years, and no wolves have been killed.

Stan Boyd, executive director of the Idaho Wool Growers Association, said his group works with members to help them deter wolves without shooting the animals. But he still sees guns as critical tools, and he says wolf problems have declined recently as the number of Idaho wolves has gone down.

"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."

In Washington state, the state's Department of Fish and Wildlife, which paid for Wielgus's research, is waiting for him to complete a broader examination of all options for managing wolves, said John Pierce, the department's chief wildlife scientist. "In the long run, we definitely would prefer to do nonlethal removal if we can figure out how it works," Pierce said.

Meanwhile, all eyes are on the Huckleberry Pack. In the aftermath of the shooting of the lead female, will fewer sheep die in wolf attacks—or more?

Correction: An earlier version of this story incorrectly said the U.S. Fish and Wildlife Service funded Rob Wielgus's research. It was the Washington Department of Fish and Wildlife, and John Pierce works for that department.

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