Brucellosis creates political uproar over Yellowstone bison herd

Bison population by year. Bars represent culls.

Bison population by year. Bars represent culls. From Dobson, et al. (1996)

Well, at least that’s my take. Most people would probably point to humans when talking about political problems. Here, though, I’m going to blame the bacteria.

Bison were once found across most of the middle and western United States and Canada, but were nearly hunted to extinction in the 19th century. Expansionists sought to cut off Native American food supplies and the Industrial revolution created an intense demand for buffalo hides, which were used for belts to run large machinery.

Fortunately, a few conservationists saved the fewer than 25 animals who remained in the wild in Yellowstone Park. In 1902, captive bison were introduced into the park to increase the genetic viability of the herd. Populations were managed and regulated until 1966 after which the herd was allowed to expand naturally.

However, climate change and food scarcity has caused some of the expanding population to move out of the park in search of grazing lands.

This is a real problem for cattle herders. Bison are thought to be the largest reservoir of Brucellosis in the United States, despite decades of effort to eliminate the disease. When bison roll into cattle ranches, bacteria can spread from bison to cattle.

Bison appear to suffer little from the disease, but in cattle, spontaneous abortions are likely, resulting in major economic losses to livestock producers. When cattle test positive for the disease, they are culled immediately. The US government compensates the farmer for the loss.

Bison who leave the park and wander into neighboring Montana threaten the state’s Brucella free status. If Montana were to lose that status, all cattle exported from Montana would have to be tested and certified Brucella free, which would increase costs to livestock producers.

Park managers have considered culling the herd, and reducing its size to a more manageable 3000 animals. They propose killing several hundred of the animals which are in the vicinity of Montana’s border as both a precaution and a way to scale back the bison population. The carcasses will be sold as meat.

And this is where environmentalists come it. Several organizations have sprung up around the issue. Most notably, a man chained himself to a 55 gallon drum filled with concrete to prevent more bison from being killed and shipped off the slaughter. Hoping to avoid an escalating political confrontation, the authorities called off the cull.

Opponents of the cull claim that Yellowstone can support more than 6000 bison, far over the target population size of 3000. Proponents argue that the park may theoretically support more than 3000, but a larger herd means that it is more likely that bison will wander into Montana in search of food. The risk there, of course, is that Brucella will be brought into Montana. It is conceivable (to me) that this whole row wouldn’t exist without Brucellosis.

I’m especially interested in the issue because it parallels similar problems in Laikipia, Kenya. Livestock producers and conservationists are constantly in conflict over issues of land rights, economic impacts of disease threats, the rights of wildlife and strategies to protect it in increasingly crowded and rapidly changing areas of the world.

Given the very different perspectives of conservationists and ranchers, no solution has been found in Kenya yet. I’m doubting that one will be found in Yellowstone. Environmentalists are taking this as a moral issue (save the bison!), conservationists are approaching this as a practical issue (manage the herds properly and stay out of the political debate) and herders speak to economic issues (Brucella threatens my business).

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About Pete Larson

Assistant Professor of Epidemiology at the Nagasaki University Institute for Tropical Medicine

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