Associated Press

BOZEMAN, Mont. — Snowmobiles cause enough stress on wolves and elk in Yellowstone and other national parks that it may harm their reproductive and immune systems, a Montana State University study has found.

The peer-reviewed study, published in the June issue of Conservation Biology, is the first evidence to confirm some suspicions of the National Park Service biologists who requested it.

The elk and wolf populations that were studied in three national parks are stable so far, said study leader Scott Creel, associate professor of ecology at MSU.

"That probably means they can compensate for the level of response we're seeing now," he said. "But in my opinion, it raises the question: How much more can they compensate for?"

He said the stress responses of the elk and wolves get stronger as snowmobile use increases.

The National Park Service is reconsidering a planned ban on snowmobiles in Yellowstone and Grand Teton national parks. Much of the debate has focused on what effects snowmobiles have on wildlife and air quality.

The MSU study began after the Park Service asked for an assessment of the effect of snowmobiling on elk and bison. The study was eventually expanded to include wolves.

The bison portion of the study isn't finished yet, but Creel said bison stress hormones don't appear to be affected by snowmobiling.

Researchers found that stress hormones known as glucocorticoids tend to increase in wolves and elk when snowmobiles are present. Over time, sustained stress can cause the elk or wolves to start burning energy that is meant to be stored, and that affects "all sorts of systems," Creel said.

"When those levels are chronically elevated, it can shut down reproductive systems and immune systems," Creel said.

Researchers collected 125 samples of elk droppings between West Yellowstone and Old Faithful during the snowmobile season and just afterward, when wheeled vehicles were using the road. The pellets were then examined for glucocorticoids.

Creel said scientists accounted for other factors that might stress the elk — primarily age and snow depth — and then compared the data with snowmobile use in those areas.

"On the days when snowmobile use was higher, stress levels were higher," he said.

The results also suggested that elk were more stressed around snowmobiles than automobiles.

In examining the effect on wolves, researchers looked at three national parks with wolves: Voyageurs in Minnesota, which allows snowmobiling; Isle Royale in Michigan, an island which is closed to the public in the winter; and Yellowstone's Northern Range, which is closed to snowmobiles but open to automobiles.

Wolves had higher stress levels in Voyageurs than in Isle Royale. Also, the study showed the stress increased in line with snowmobile use in Voyageurs, doubling in 1999 when use was heavy and increasing by one-third when use was "relatively light" in 2000.

"You see a pretty clear effect of snowmobiling," Creel said.

The study said stress levels were intermediate in wolves on Yellowstone's Northern Range where cars are allowed but not snowmobiles.

Creel said all vertebrates have a similar physiological response to stress. First, adrenaline is secreted. Over longer periods of time, glucocorticoids are released, which means the body becomes less efficient because it has to use stored-up energy.

That process can take a toll on other bodily functions, including reproduction and the ability to fight off diseases.

June 2, 2002

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