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The battle over bison.

More than 60 million bison once roamed the grasslands of North America. They had long been important to the Native American tribes of the Great Plains and were an integral part of the landscape when European settlers first explored the region. Valued for their meat and hides, bison were heavily exploited, and by the late 1800s, fewer than 1,000 remained.

A few native bison found sanctuary in the newly established Yellowstone National Park. From an estimated 25 individuals in 1900, the herd has grown to more than 4,000 animals and is today the largest continuously free-roaming herd of bison found in the United States.

Another 225 bison roam in Grand Teton National Park, part of the 18-million-acre Greater Yellowstone Ecosystem. These bison herds are one of the ecosystem's unique wildlife assets.

Yet, Greater Yellowstone's herds are threatened more today than at any time in this century. Since 1985 more than 1,500 Yellowstone bison have been killed after wandering from the park. Although some have been shot on private lands, many have been killed on public lands that were set aside for wildlife management. The animals are being slaughtered to appease regional livestock industry officials, who claim that bison could transmit the disease brucellosis to domestic livestock.

The destruction of bison has ignited a nationwide furor and appears to pit the livestock industry, and the state of Montana in particular, against the National Park Service (NPS). Depending on the outcome, the bison-brucellosis issue may jeopardize NPS control of wildlife within park units and threaten free-roaming wildlife everywhere.

The focus of the controversy is Brucella abortus, a bacterium that can cause abortions in cattle, particularly with first-time pregnancy. It can, on occasion, infect humans as well, where it is called undulant fever for the varying intensity of symptoms. Besides domestic livestock, the disease is known to be carried by many wildlife species, although it appears to have little effect on them.

No one disputes that some bison and elk carry the disease, but the risk of transmission to domestic animals is extremely remote. Dr. Margaret Meyer, a brucellosis specialist at the University of California's Davis School of Veterinary Medicine, and Mary Meagher, a biologist with the National Biological Service, points out that there is a vast difference between infected and infectious. Most brucellosis testing involves looking for antibodies. But the presence of antibodies is not a good indicator of active brucella infection in bison; it merely means that at some point in its life the bison was exposed to brucellosis.

The actual culture of brucella bacteria from bison organs is the only reliable measure of infection rate, says Meagher. But culturing bacteria is a much more expensive and time-consuming test, and it is seldom done. Although the national and local media regularly report that 50 percent of Yellowstone's bison "test positive" for brucellosis, what this really means is that 50 percent have antibodies to the disease. In reality, a much smaller percentage actually carry active brucella bacteria.

A key assertion of Meagher is that the brucella bacterium behaves differently in bison than in cattle. She claims that assumptions about its transmission pathways, based on studies of domestic livestock, may be invalid. Meyer and Meagher theorize that bison calves are inoculated with brucella bacteria through their mother's milk. Gradually young bison acquire antibodies, and hence resistance, to the disease. This may explain why brucellosis does not appear to cause abortions in mature free-ranging bison cows.

Countering Meyer and Meagher is Dr. Clarence Siroky, Montana State Veterinarian, who cites an experiment done in Texas where brucellosis inoculated into captive bison was successfully transferred to cattle. That study, however, was debunked by Meagher and Meyer. They argue that laboratory experiments do not mimic field conditions. For example, the bison were given a very large dose of brucella, which Meagher and Meyer suggest caused "distortion and magnification" of results. Furthermore, under field conditions, brucellosis transmission between animals is done orally, and the Texas experiment used a different transfer method. Without field testing, Meagher and Meyer believe conclusions about brucellosis transmission risk are more theoretical than real.

A "field test" of the degree of risk, albeit an unplanned one, occurred in the winter of 1989. More than 900 bison migrated out of Yellowstone and scattered among cattle north of the park. The state of Montana later tested 20 cattle herds for brucellosis and found no evidence of the disease. "The state is saying this is a grave threat, and here you had all these bison come out of the park to mingle with livestock and nothing happened," says John Mack, an NPS wildlife biologist working on the bison-brucellosis issue. "This comes back to the basic question being asked: what is the real risk?"

Risk is limited by a number of factors. For physiological and anatomical reasons, bison bulls cannot transmit the disease to domestic animals.

And a surprisingly few female bison can potentially transmit the disease. The major mechanism for transmission between animals is by contact with birth fluids of infected females, typically when or immediately after it aborts a fetus. A female bison cannot transmit the bacteria, even active ones, unless they are located in her reproductive organs. The odds that cattle would have an opportunity to come upon an infected fetus are remote to begin with; scavenging animals make quick work of any aborted calves. But central to the issue is the fact that there is virtually no documented evidence that free-roaming bison respond to brucellosis infection by aborting.

This brings bison proponents back to the question of risk. Even if free-roaming bison can transmit brucellosis to cattle--as yet an unproven assertion--how likely is it to occur?

Some idea of the risk can be assessed by noting that of 218 bison killed outside of Yellowstone in 1991-92 and culture tested for the presence of brucellosis, only 27 actually carried the disease. But 19 were bulls and unable to pass the disease on to domestic animals. Of the eight females that tested positive, only one--a yearling, too young to reproduce--had the brucella bacteria present in the reproductive tract. Thus, out of 218 bison killed, none was capable of transmitting the disease to livestock.

Statistics such as these suggest that the risk of brucellosis transmission from bison is extremely small, if it exists at all. According to Mack, "There is no evidence of wild free-roaming bison transmitting brucellosis to cattle."

One perspective on the brucellosis conflict is that it may mask a deeper philosophical debate about who controls the West. Some livestock producers may be trying to assert control over wildlife to prevent native herbivores from competing with their herds for public forage and space.

One Wyoming Game and Fish official close to the issue who asked not to be named says, "If the public gets used to the idea that bison, like elk and deer, should be free to roam on federal lands managed by the Forest Service and Bureau of Land Management, then it may lead to a reduction in the amount of public lands forage allotted to livestock. That's what the ranchers really fear," he says.

The evidence to support such a view is circumstantial but abundant. This past winter, for example, the Montana legislature (dominated by agricultural interests) removed bison from the management authority of the state's department of Fish, Wildlife and Parks and transferred it to the Department of Livestock, which has since indicated an unwillingness to let any wild bison enter the state, especially west of Yellowstone. The Department of Livestock has killed nearly all bison that have wandered west of Yellowstone and many that have wandered north--more than 400 animals this year alone.

Coinciding with the state's stepped-up bison slaughter policy, Sen. Conrad Burns (R-Mont.) introduced a bill that requires the year-round capture of Yellowstone bison. The animals will be tested for brucellosis, with those testing positive slaughtered or neutered. The bill also requires NPS to significantly reduce its bison herds--whether or not brucellosis is detected--to a yet-to-be-determined number.

Even though the Park Service is currently working on a bison management plan, the state of Montana filed a suit against the federal departments of interior and agriculture, alleging that NPS was ignoring the threat to livestock posed by bison and that the Animal and Plant Health Inspection Service (APHIS) was threatening loss of the state's brucellosis-free status. At the end of July, NPS and APHIS proposed an out-of-court settlement to the suit that, among other things, would have required some testing and slaughter of animals. But it also permitted bison not posing any immediate threat to domestic livestock to roam on some public lands outside of the park. The state rejected the proposal.

According to Wyoming Game and Fish veterinarian Tom Thorne, two things appear to be driving the issue: the recent attainment of brucellosis-free status by states surrounding Yellowstone and the growth of wildlife populations in the Greater Yellowstone Ecosystem.

Brucellosis-free status has economic implications. It permits cattle producers to transport animals freely across borders, without the need for brucellosis testing. These states now seek to maintain that status, and officials there fear that it could be jeopardized by the presence of brucellosis among wildlife.

The second reason for the controversy, according to Thorne, is the growth of wildlife populations throughout the Yellowstone ecosystem, which increases the likelihood that wildlife and livestock will come in contact.

Expansion of Yellowstone's bison herd to record numbers is attributable to several factors. First, mild winters for the past decade have led to greater winter survival and higher calf production. At the same time, winter snowmobile use has also increased. Some think a connection exists between the snow-packed trails created by snowmobiles and the bison herd's new-found mobility and growth.

Travel on snow-packed roads saves bison a tremendous amount of energy, according to Meagher. Ultimately this not only results in greater winter survival but also facilitates movement within park borders and beyond, where snow depths are typically lower than in the park. Unfortunately for many park bison, the winter migration is often a one-way journey. When the shaggy beasts travel beyond the protection of Yellowstone's borders, most are killed by state officials.

When asked about the contribution of snowmobiles to the problem, Siroky dismissed the argument as invalid. The problem is bison, he insisted.

Livestock interests feel their position is justified. After all, they point out, since the USDA began its brucellosis eradication program in the 1930s, more than $3 billion of taxpayer funds have been spent trying to eliminate the disease from the nation's cattle herds. Originally, the expenditure was justified by human health concerns. Most people contracted brucellosis or undulant fever from drinking raw milk; however, milk pasteurization largely eliminated this source of infection in the 1940s. Even though human health risks are minimal today, the program has continued to enjoy taxpayer support. D.J. Schubert of the Fund for Animals notes that this support amounts to a huge taxpayer subsidy to the livestock industry because it is aimed at reducing the loss of calves to abortion--a real economic cost to cattle producers, but hardly a concern to most citizens.

But Siroky claims that the human health issue is still the key factor. "If brucellosis did not cause a [human] health problem, it would not be a problem," he says. Sen. Burns echoed this point in an editorial in the Bozeman Chronicle suggesting that people visiting Yellowstone might get the disease.

Thorne says the health threat to tourists or anyone else is "pretty low, almost negligible." The only way a tourist could contract the disease, says Thorne, is by contact with an aborted fetus that also happened to have active brucella bacteria--an extremely unlikely occurrence. Contracting the disease from meat is also unlikely since the bacteria are destroyed in the cooking process. According to the Centers for Disease Control and Prevention, no more than 100 cases of undulant fever are reported each year in the United States--most occurring among slaughterhouse workers. The disease, which can cause painful arthritis, inflammation, and fever, is readily treated with antibiotics.

Joe Bohne, a biologist with the Wyoming Game and Fish Department, points out that more than 40 percent of the elk in Jackson reportedly carry brucellosis, and last year 4,300 were killed by hunters. "Most of us around here are gutting our animals without gloves--don't you think if brucellosis transmission were as great a risk as implied, the USDA would have health warnings for elk hunters?" he asks.

Moreover, despite the fact that so many elk wintering in the Jackson area carry the disease, they are not a target of the livestock industry's ire. According to one state biologist, this is because elk have many supporters among hunters and outfitters--again suggesting that control of disease transmission is not the primary goal.

Siroky has a different explanation. He believes that park bison are the source of elk infections. "Once we control the disease among bison, elk won't get it anymore," he asserts. This is one of the key premises underlying the Burns bill's focus on bison.

Controlling brucellosis among free-roaming animals spread over an 18-million-acre ecosystem may not be possible, but preventive measures are available.

First, vaccination of all livestock against brucellosis could be made mandatory, not discretionary as it is now. Even though the vaccine is not 100 percent effective, it would still significantly reduce any risk to livestock.

Second, keeping cattle off winter ranges and spring calving areas of bison and elk could largely halt any potential for transmission.

Third, closure of Yellowstone and Grand Teton national parks to snowmobile use would eliminate snow-packed passageways that aid bison in leaving the parks and would restore winter mortality of bison to natural levels. If natural processes are allowed to control bison populations, artificial measures such as shooting become unnecessary.

In addition to all these measures, some movement toward control, if not outright eradication, of brucellosis among wildlife is under way. Researchers hope to develop an oral vaccine that could be scattered on elk and bison winter ranges. Currently, no effective vaccine exists for bison.

And in Wyoming, the Game and Fish Department has experimented with a vaccine aimed at elk concentrated at winter feed grounds. According to Thorne, elk at one Wyoming feeding ground showed a decline in infection from 46 percent to 9 percent as a result of the vaccine.

All of these measures, taken together, should significantly allay livestock producers' fears of economic hardship--if that is the real concern. But if brucellosis is nothing more than an excuse to control public lands and limit wildlife, then no solution is likely to satisfy livestock advocates, and the threat to Yellowstone's wildlife is far greater than most people imagine.


Terri Martin, NPCA's Rocky Mountain regional director, says, "Free-roaming bison are central parts of the visitor experience and ecology of the Greater Yellowstone. The testing and slaughter proposals are outrageous attacks on our national parks as wildlife sanctuaries." NPCA is working to defeat the plan to slaughter thousands of bison in Yellowstone and Grand Teton national parks, and you can help.

Write to the governors of Montana, Wyoming, and Idaho. Urge them to abandon the goal of eradicating brucellosis in wildlife through massive slaughter of bison. Recommend that they pursue more reasonable measures, such as vaccinating cattle and temporarily keeping them off bison winter ranges and calving areas on public lands.

Gov. Jim Geringer State Capitol Cheyenne, WY 82002

Gov. Marc Racicot State Capitol Helena, MT 59620

Gov. Phil Batt State House Boise, ID 83720

GEORGE WUERTHNER is a wildlife biologist, freelance writer, and photographer based in Oregon.
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Copyright 1995 Gale, Cengage Learning. All rights reserved.

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Title Annotation:includes related information
Author:Wuerthner, George
Publication:National Parks
Date:Nov 1, 1995
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