Bison Herd Changing Ecosystem

The famous and often controversial Yellowstone bison herds are changing the ecosystem around them as they move steadily to the west, according to Mary Meagher, a retired National Park Service biologist who has studied the bison for 40 years.

"We're seeing an ecosystem change," Meagher told a scientific conference at Mammoth Hot Springs Tuesday. "We're 20 years into it."

Her report was based on 151 aerial surveys of bison, counts she completed at various times of the year between 1970 and 1997.

Her talk focused on bison in the Pelican Valley, north of Yellowstone Lake. The valley has some of the harshest winter environment in North America, but is a place where bison were able to scratch out a survival by sticking close to geothermal areas, where the snow is thinner and the temperatures are warmer.

Historically, about 100 bison survived the winter there. But in recent years, that number has dwindled to a comparative handful.

That's because Pelican Valley bison were able to use groomed snowmobile and snowcoach roads to travel west to the Hayden Valley, she said.

That travel began what she called a "domino effect," boosting the summer bison numbers in the Hayden, which was traditional winter range. The phenomena sent more bison to the Firehole Valley on the park's west side, while fewer bison have been using the Hayden Valley in the winter, she said.

From the Firehole Valley, they have been steadily spilling out of the park's western border, where they are hazed, trapped or shot by state and federal officials concerned about the spread of the disease brucellosis to domestic livestock.

"Bison are in odd places," she said. "Places they have no business being at different times of the year."

Already this year hundreds of bison are gathered in the Firehole and west of that drainage, setting the stage for the possibility of a big exodus this winter. At least one big bull had already left the park last week.

There are about 3,000 bison now in the park, and it won't necessarily take a severe winter to drive them out of the park, Meagher said in an interview.

"It will not take the kind of winter we had in 1996-97 to produce the kindof results we had (at that time)," she said.

About 1,200 bison were shot or trapped and shipped to slaughter that winter. Hundreds more died in the harsh winter conditions.

Meagher's data, while extensive, is not universally accepted.

Dan Bjornlie, now with the Wyoming Department of Game and Fish in Lander, also has studied the relationship of bison and roads.

His data, gathered over two years, found that most bison movements from east to west occur when the roads aren't being groomed, he said Wednesday.

"To a point, I think there are some fairly major contradictions" between my research and Meagher's, he said.

Even if Meagher's conclusions became universally accepted, there's no guarantee they'd be reflected in how bison and roads are managed, although a Park Service spokesman said Wednesday the government is willing to listen.

"As new information, or evaluation of old information, comes in, that can be used to help make decisions in the future," said Yellowstone spokeswoman Marsha Karle. "I don't know if her information will affect future management or not."

The impacts go beyond bison, Meagher added.

The Firehole Valley, named for its abundant thermal features, is not good winter bison habitat, she said, but bison are spending lots of time there, making changes in how the ecosystem works.

Those changes include soil compaction, which affects communities of plants and other creatures, including complicated and poorly understood systems in and near geothermal features.

State and federal officials last year signed a new bison management plan, one that calls for increased reliance on hazing bison instead of killing them. However, that plan has not yet been tested by movements of large numbers of bison.

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