Wolf return sends mule deer to higher terrain

(Credit: Getty Images)

As gray wolves continue to make a strong comeback in Washington state, deer have had to change their tactics to stay alive, research finds.

Wolves will chase white-tailed deer and mule deer great distances—sometimes upwards of 6 miles (10 kilometers)—in search of a satisfying meal. How these two deer species respond to the threat in the early years of this predator’s return could shed light on changes to their behavior and numbers.

For a new study, which appears in Oecologia, researchers monitored the behavior and activity of wolves and deer in Washington for three years. They learned that to avoid getting caught, mule deer, in particular, spend more time away from roads, at higher elevations, and in rockier landscapes.

“In any particular ecosystem, if you have a predator returning, prey are unlikely to all respond similarly,” says senior author Aaron Wirsing, an associate professor in the University of Washington School of Environmental and Forest Sciences. “We show that wolves don’t have a uniform effect on different deer species.”

Means of escape

Wolves were completely wiped out from Washington early in the last century, but began returning to the state from Idaho, Montana, and Canada about a decade ago. The latest estimates now show about 200 wolves in packs across eastern Washington.

Both white-tailed and mule deer are important food for gray wolves. While they might look similar to an untrained eye, white-tailed deer and mule deer are very different animals: Mule deer are bigger, with large, dark ears, and a black-tipped tail. White-tailed deer are smaller animals, boasting an unmistakably long tail with a white underside that stands straight up when the deer feels alarmed.

Aside from their physical characteristics, the two species also differ in how they escape from predators. When chased, mule deer “stot,” a quick bound with all four legs touching the ground at the same time. This bounding gait helps them negotiate all types of terrain and gives them an agility advantage in rocky, uneven areas where other animals might find it hard to run.

By contrast, white-tailed deer sprint away from predators and rely on spotting them early enough to try to outrun them.

Moving out

Keeping these known escape tactics in mind, researchers focused on the “flight behavior” of deer living in areas where wolves have returned and in areas without wolves. The researchers chose four distinct study areas, all near the small town of Republic, Washington. Both species of deer live in all four areas, but known wolf packs only occupied two of them at the time of the study.

Researchers set up wildlife cameras, captured and put collars on wolves and deer, and monitored the data from all of the collars from 2013 to 2016.

“That part of eastern Washington is really special,” says lead author Justin Dellinger, who completed the work as a doctoral student and now works at the California Department of Fish and Wildlife. “There is huge diversity of large mammals, including all of the native prey populations like big horn sheep, moose, and deer. And now we’re starting to see a full complement of native predators, like wolves, here as well.”

Overall, researchers found that mule deer in gray wolf areas changed their behavior to avoid wolves altogether—mainly by moving to higher, steeper elevations, away from roads, and toward brushy, rocky terrain.

On the other hand, white-tailed deer that favor sprinting and early detection as ways to escape from predators stuck to their normal behavior in wolf areas, sprinting across open, gently rolling terrain with good visibility—including along roads.

“Mule deer faced with the threat of wolves are really changing their home ranges, on a large scale,” Wirsing says. “They appear to have shifted kilometers away from where they had been prior to the return of wolves, generally going up higher where the terrain is less smooth and where wolves are less likely to hunt successfully.”

These larger shifts among mule deer could affect hunting opportunities. Indeed, some hunters in eastern Washington have already reported seeing mule deer higher on ridges where they are less accessible than in past years, Wirsing says. Hunting for white-tailed deer likely won’t change to the same degree with the presence of wolves, the results suggest.

Long term, changes among mule deer in wolf areas could affect other parts of the ecosystem, and perhaps reduce the number of deer-vehicle collisions, Wirsing says.

Researchers from the Colville Tribes, the US Forest Service, Florida International University, and Oregon State University contributed to the research.

The National Science Foundation, the Safari Club International Foundation, Conservation Northwest, Washington Department of Fish and Wildlife, and the University of Washington funded the work.

Source: University of Washington