In winter the mountains west of Whitehorse are often a busy place as the high plateaus and broad valleys are ideal for everything from dog mushing to snowmobiling.

Todd Powell can tell you first hand just how busy it can get; last winter he spent almost four months in the area, camping there half the time and driving up daily from Whitehorse for the rest of it.

He also has a good idea of how often people encounter animals from the Ibex Caribou Herd while recreating in the area. "It is pretty common to see caribou up there," he says. "On a high use weekend, for example, a group of caribou might encounter snowmobilers every half hour."

Powell has taken time off from his job with the Yukon government's Wildlife Viewing program to complete a master's degree at the Université de Sherbrooke in Québec.

He is studying encounters between backcountry travellers and caribou, trying to determine how much winter recreation affects the caribou, and how snowmobilers could reduce some of those effects by making simple changes in behaviour.

Biologists are concerned that the Ibex Herd has not steadily grown in size even though hunting in the area has been banned since 1993 as part of the Southern Lakes Caribou Recovery Program.

The Ibex Herd increased almost 200 percent during the first five years of the recovery program, but has grown very little in size since then and numbers only about 450 animals today.

Meanwhile, the Carcross and Atlin herds, which are also part of the Southern Lakes program, have continued to increase their numbers.

"Something is happening with the Ibex herd and we don't know if it is the environment or recreation impacts or the unusual springs that we've had for a couple of years, but it would be ideal to get the herd to a more robust size."

Lots of research has already been done on interactions between wildlife and humans, and -- surprisingly enough -- skiers and snowshoers can spook caribou more than people riding a snowmachine.

"People on foot or on skis can get a bigger reaction than a snowmobiler because a snowmobile does not have a typical predator shape," says Powell. "Caribou may not recognize them as an obvious threat as quickly."

Recognizing known threats also explains why the sudden appearance of a dog team can alarm caribou. "With dog teams, all of a sudden you have a whole line of what look like predators coming down the hill. Pet dogs running loose are also a problem."

Powell ended up focusing his research on snowmobilers as they encounter caribou more often than any other group. There are more of them using the area and they can cover big distances in a short time.

As well as observing other snowmobilers, he spent a lot of time on a snowmachine himself recreating typical encounters. "We tried to mimic what was already happening, and recorded reaction distances and changes in behaviour."

He found that caribou frequenting areas popular with snowmobilers were not more nervous than ones using quieter areas, as he thought would be the case.

"These caribou are not more jittery when the snowmobilers are not there. After a snowmobile passes there is a bit of a lag time before they settle down again -- maybe 10 to 20 minutes."

"It's not a big deal when caribou only see one snowmobile a week. The problems start when the snowmobile use is really high."

Caribou are nychthemeral, meaning that they feed day and night, so they can easily make up for a bit of feeding time lost to disturbance. But they can be stressed by repeated encounters.

The good news is that mainly bull caribou frequent the popular snowmobiling areas on the Golden Horn and Mt. McIntyre plateaus. The cows and calves -- which are more vulnerable to stress -- winter in more out of the way places.

The bad news is that snowmobile trails offer a major advantage to wolves, caribou's main predators. While caribou don't benefit from the trails, wolves use them like highways.

"We tracked wolves for 12 kilometres on one trail; they just headed straight down the trail and were able to scope out two valleys using the same trail."

That makes hunting easier for the two packs of wolves that roam the area, preying mainly on caribou as there are very few moose in the area.

As part of his thesis, Powell will make a number of specific recommendations for snowmobilers using the Ibex area. His main suggestion is that they stay on existing trails rather than creating new ones.

Also, he hopes that people will recognize that caribou winter range is not a good place to play. "The terrain up there allows people to go everywhere, and while it is very rewarding to be able to cruise over the mountains and play in the bowls, unfortunately it does have an effect."

Finally, he suggests that people keep their distance -- at least 500 metres, preferably downwind -- and not stare at the animals for too long. The caribou will stare back and may flee, using up stores of energy that they need to survive a Yukon winter.

"It is possible to coexist with the caribou. We're hoping that if people can modify their behaviour, then the caribou can get as much benefit as possible from the habitat."

Todd Powell can be contacted at tpowell@sympatico.ca. In February he will return to his job with the Wildlife Viewing program.