Tourists’ Impact Weighed Where the Buffalo Roam

On a groomed, snowy trail in the middle of winter, men on snowmobiles pass almost within arm’s reach of a herd of swaggering bison. The beasts do not so much as flinch when the noisy machines slowly pass.

It seems a peaceful coexistence: resident and traveler enveloped by the snow-draped majesty deep inside America’s first national park, sharing the same narrow path without conflict.

But for some researchers, this scene that is repeated almost daily during winter months masks a complex problem that raises questions about the road ahead for the bison of Yellowstone.

Some who study the animals believe that making the park accessible to people in winter by maintaining groomed trails used by snowmobiles has contributed to a change in the bison’s natural migration. Maybe more important, they say, the policy may have disrupted the best natural population control of the lumbering beasts--winter.

“Winter used to keep the lid on” the bison, says Mary Meagher, a retired ecologist who studied the animals in Yellowstone during nearly 40 years with the National Park Service.

That agency, now considering banning snowmobiles from Yellowstone and nearby Grand Teton national parks, has been in conflict with the state of Montana over how to manage the animals.

Supporters of the proposed ban usually cite air and noise pollution from snowmobiles, and concerns about the occasional rider who harasses or chases wildlife. But Meagher believes that’s only one aspect of a greater problem.

The hard, compacted trails allow bison to move with greater ease during winter, she says. Instead of trudging through deep powder, the animals take the path of least resistance, expending less energy so that fewer die off naturally over the harsh winter.

The increased bison populations and the changed travel patterns may help explain why, beginning some years ago, more of the animals started leaving the park in search of food, she says.

Many enter Montana, where ranchers and state agriculture officials fear that the bison will infect cattle herds with brucellosis, a disease that causes cows to abort their calves and can cause undulant fever in humans. Hundreds of bison outside the park have been killed.

Meagher suggests possibly designating trails and viewing areas for winter tourists but closing other areas to force bison to “relearn” historic travel patterns. She acknowledges that no clear cause-effect link has emerged from her data collected over 27 years; other shorter-term work has contradicted her assertion.

But she says: “Nothing I’m seeing will change my belief that something is happening with the bison population. I do know where it’s going, I just don’t know how far down.”

Tom Olliff, branch chief of natural resources at Yellowstone, says additional research is needed before any direct link can be made between the use of groomed trails in the park and bison. “The jury is still out,” he says.

But the park has taken steps to minimize the effects of snowmobile noise and pollution concerns, he says. Yellowstone attracts about 62,000 snowmobilers a year.

“The problem is, you can detect the effects of recreation on an individual animal. You can see behavior changes, a response from the bison. You can detect stress,” he says. “What’s difficult to do is link it to a population.”

Once dwindling in numbers, bison in the West have come back in recent decades.

They have long been a touchy subject around Yellowstone.

In the winter of 1996-97, the population in the park was estimated at 3,400. During that same season, nearly 1,100 bison were killed by state and federal management officials when they left the park and entered Montana. They were slaughtered under a plan that angered conservationists and animal-rights groups.

After years of work, Montana, the Park Service and other agencies agreed in December 2000 on a management plan that is intended to maintain a population of up to 3,000 bison, and allows the animals to seek winter range outside the park.

If too many leave during winter, state and park monitors use helicopters and snowmobiles to try to haze them back inside Yellowstone’s borders. If that doesn’t work, the animals are captured and tested for brucellosis.

Of the 34 bison captured this year after hazing efforts failed, 23 tested positive for brucellosis and were slaughtered, according to Montana’s Department of Livestock.

Environmentalists and animal-rights groups say hazing is stressful for wild animals and unnecessary; they say there has never been a confirmed case of cattle contracting brucellosis from bison in the wild. But scientists and management officials say a risk exists and are seeking ways to mitigate it.

Peter Gogan, a wildlife biologist with the U.S. Geological Survey, has studied Yellowstone’s bison and says it is natural that the animals have expanded their range as their numbers have grown in the last 20 years. But whether that growth is caused by groomed trails or a combination of factors, including climate and the social tendencies of bison, remains unclear, he said.

The Clinton administration, citing pollution concerns, proposed phasing out all recreational snowmobile use in the park by winter 2003-2004.

Under pressure, the Bush administration backed away from that plan and agreed to have the Park Service conduct another environmental study, which is scheduled to be available for public comment by March 29.

The new study’s four options are:

* Keeping Clinton’s plan.

* Keeping Clinton’s rules but delaying their effect.

* Permitting unguided snowmobiling if the machines are quieter and less polluting.

* Permitting only guided snowmobile tours, and only if those machines meet stricter noise and pollution standards. The number of snowmobiles allowed to enter the parks would be limited.

A final decision is expected by November.

Meanwhile, Yellowstone officials continue trying to balance their mandate of protecting the park’s wildlife while maintaining the public’s right to visit.

“Almost every question becomes a controversy,” said John Sacklin, the park’s chief of planning and compliance. “There are no simple answers and they’re not easily resolved.”