BILLINGS, Mont. — With Yellowstone National Park's bison population at its highest level in years, some environmentalists fear that huge numbers of the beasts will wander into Montana this winter and be killed in the name of controlling disease.
Fueling their concerns is a recent spell of harsh weather -- hard winters historically have led to more bison leaving the park in search of food -- and fears that officials will take a hard line against bison after a Wyoming cattle herd was found to be infected with brucellosis, a disease also present in the Yellowstone bison herd.
"We're in for yet another winter of tragic and unnecessary killing by state and federal agencies mismanaging bison over a perceived risk of the transmission of brucellosis to cattle," said D. J. Schubert, a wildlife biologist for the Fund for Animals.
Officials with the park and Montana's Department of Livestock say that although they can't predict just how the season will play out, they will do what is necessary to minimize a risk that they say is real. Those actions will include capturing and testing bison for the disease and sending animals to slaughter.
Under a joint state-federal bison management plan, bison that cannot be forced back into the park are captured and tested for brucellosis. Animals testing positive are sent to slaughter. If the park's population exceeds 3,000 animals by late winter and early spring each year, bison that stray into Montana can be killed without being tested first, said Rick Wallen, a wildlife biologist at Yellowstone.
There are now more than 4,200 bison in the park, which park officials say is the highest in nearly a decade.
That worries conservationists like Tony Jewett. He said the exit of large numbers of bison -- which he considers a possibility if the winter is severe -- could quickly overwhelm state and federal officials outside the park.
"I think we're setting ourselves up for a situation that could be deadly for the bison," said Jewett, senior director for the Northern Rockies region of the National Parks Conservation Assn.
Last season, about 250 bison were sent to slaughter. And in the winter of 2001-02, 199 bison were slaughtered, according to the Montana Department of Livestock.
Josh Osher, a coordinator with the Buffalo Field Campaign, a group that tries to protect wandering bison, believes that large numbers will leave the park, particularly as spring begins, and that many of them will die.
"They are already gunning for them," he said.
Osher and Schubert are among those who believe that the brucellosis in a Wyoming cattle herd, although apparently not related to bison, could cause officials to take a harder line when dealing with bison that enter Montana. If Montana loses its official brucellosis-free status, state ranchers would have to undertake costly screening tests when they sell their cattle.
Karen Cooper, spokeswoman for the Livestock Department, said decisions will be based on several factors, including weather conditions and the number of bison involved.
Wandering bison concern ranchers and state livestock officials who worry that the animals will infect cattle with brucellosis, a disease that causes cows to abort their calves and can cause undulant fever in people. The bison defenders say there has never been a documented case of bison transmitting brucellosis to cattle in the wild.
If Montana cattle were to be infected, it could also have devastating economic effects, said Steve Pilcher, executive vice president with the Montana Stockgrowers Assn.
"It's not our objective to eliminate bison from Yellowstone National Park. We realize they're a rich part of our history and that's the farthest thing from our mind," he said. "But we feel the park and government have a responsibility to address the disease issue."
Researcher Jim Knight, who has studied bison at the park, agreed. But he said he sees officials making "no real dent" in the brucellosis issue soon.
"As long as there are any bison with brucellosis, it will spread," said Knight, an extension wildlife specialist at Montana State University in Bozeman.
The Park Service is ready this year to vaccinate young bison that test negative if they are captured near the park's northern boundary, Wallen said. Scientists have told park officials that the vaccine, which is labeled for use in livestock, is safe to use but, "like with many vaccines, is not 100% effective," he said.
Conservationists like Schubert oppose this, citing concerns with the efficacy and with treating bison like livestock rather than wildlife.
Wildlife officials in Montana are considering allowing hunters to kill bison. If the hunt were approved, it could be in place by next season.
Supporters say a hunt would validate bison as a wildlife species in the region. But some conservationists oppose this as well.
Wallen said the Park Service is doing its best in trying to address the brucellosis issue.
"For us to win on this issue, we'd guarantee we'd protect the herd of bison at Yellowstone National Park into perpetuity. We're not going to please everybody on the two fronts," Wallen said of environmentalists and the livestock industry. "But from our perspective, we're confident the management plan is the only feasible option for us right now to protect the bison."