Few Car Crashes with Deer in Wisconsin, Perhaps Thanks to Wolves

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Rebounding populations of gray wolves (Canis lupus) in Wisconsin are associated with reduced car accidents with deer, researchers have found. These predators frequent certain routes, or travel corridors, that include manmade roads, and the authors conclude that by keeping the deer away, the wolves did humans a favor. According to the study, published online May 24 in PNAS, counties where wolf populations returned after being wiped out in the middle of the 20th century saw declines in vehicle crashes with deer of 24 percent, on average, saving the state nearly $11 million annually.

“The icing on the cake is that wolves do this work all year long at their own expense,” Liana Zanette, an ecologist at Western University in Canada who was not involved in the study, tells The Atlantic. “It all seems like a win-win for those wolf counties.”

Because wolves prowl on roads, trails, and pipelines conveniently cleared by humans, they deter prey species from hanging about, the authors of the new study suggest. And, of course, wolves eat deer, directly reducing the numbers of deer on roadways, though this only seemed to account for about 6 percent of the decline in deer-vehicle collisions that the team documented. Overall, counties with wolves had 38 fewer deer-vehicle collisions per year by the end of the study period.

Study coauthor Jennifer Raynor, a natural-resource economist at Wesleyan University, tells Science News that there are other potential advantages of wolves, such as reducing the transmission of Lyme disease with fewer deer hosts, that the study did not address.

The importance of predators is well recognized, to the point that some regions of the US and the world have reintroduced the animals. Gray wolves were brought back to Yellowstone National Park in the mid-1990s, for example, to help restore an ecosystem ravaged by elk herbivory, among other contributing factors. The idea of introducing wolves to places with larger human populations such as Wisconsin is more controversial, but some states such as Colorado are considering it.

The benefit of seeing a reduction in deer collisions was previously suggested in a 2016 study that estimated cougars in the eastern US could contribute to about a 22 percent drop in accidents. The wolf study “adds to growing awareness that scientists should consider both the costs and the benefits of having large carnivores on the landscape,” University of Wisconsin conservation biologist Adrian Treves, who did not participate in the research, tells the Associated Press.

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