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September 25, 2009

Yellowstone Bison Hazing and Slaughter

Hazing, capturing, and slaughtering buffalo is not the answer to preventing brucellosis

The Humane Society of the United States

During the winter months, part of the bison population in Yellowstone National Park migrates outside the northern and western boundaries of the park to land (both public and private) in Montana, searching for better forage and to escape the deepest snow. During the summer months, a handful of ranchers also graze their cattle on this land, purchasing permits for the use of public lands managed by the U.S. Forest Service.

When cattle-grazing areas overlap with traditional bison migration routes and calving areas, ranchers and the Montana Department of Livestock claim that cattle are at risk of contracting brucellosis, a disease that causes spontaneous abortions in cows, even though the cattle are not present on these lands in the winter.

The National Park Service is one of several agencies using a bison management plan that allows state and federal agencies to haze bison back into Yellowstone when the animals cross the park's unmarked boundaries. The hazing practices are undoubtedly stressful for the bison, and they may also disrupt nesting eagles, potentially causing reproductive failure in these federally protected birds. Furthermore, hazing occurs in winter, when bison need to conserve energy.

As the harsh Yellowstone spring wears on and the need for forage drives more bison from the interior of the park, government agents typically switch from hazing the animals to the capture-test-slaughter strategy. All bison who test positive for brucellosis are sent to slaughter, including bulls, even though transmission is thought to occur only when an infected female gives birth or aborts.

The reality of disease risk

While some of Yellowstone's bison test positive for antibodies to brucellosis, a positive test indicates only that the bison has been exposed to the disease, which in many cases simply means that the animal has acquired disease resistance. In other words, bison who test "positive" are not necessarily infected with the disease or capable of transmitting it to other bison or to domestic cattle. Their ability to transmit the disease is even more questionable because there has never been a documented case of a wild, free-roaming bison infecting domestic cattle with brucellosis.

The already negligible risk of disease transmission is further reduced because:

  • Virtually all cattle in the area are already vaccinated against brucellosis.
  • Cattle and bison generally do not occupy the same area at the same time (bison in the winter, cattle in the summer).
  • Transmission occurs via fluids and tissues associated with either a live birth or an aborted fetus; bull bison, calves, and female bison who are not pregnant thus would not pose any threat, even if they were to come into contact with domestic cattle.


Despite this evidence, the Montana Department of Livestock and the National Park Service routinely kill bull bison, calves and non-pregnant females.

Bison are not the only wild animals in or near Yellowstone who carry brucellosis. Notably, elk in the greater Yellowstone ecosystem also carry the disease. However, only bison are subjected to the Draconian capture-test-slaughter operations that have no place in wildlife management.

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