Issue of the Week: Yellowstone Bison Management


By the late 1800s, the North American bison was nearly extinct. In 1902, the two dozen bison left in Yellowstone National Park were some of the only remaining in the wild. Thanks to a massive national restoration effort, the species has recovered to around 20,000 today. The bison, one of America’s greatest conservation success stories, is now the topic of much debate in the National Park Service (NPS) and the world of wildlife.

Bison, North America’s largest land mammal, have roamed across Yellowstone National Park in Montana since prehistoric times. Yellowstone, America’s first national park, is the only place in the lower 48 states where bison have continuously existed. Due to this pristine condition, the bison population here is extremely unique.

Yellowstone’s bison herd is the largest existing on public land and one of the only remaining that has not interbred and hybridized with domestic cattle. These 2,000 pound giants still roam free across Yellowstone, exhibiting wild behavior that other populations have lost. Bison congregate during the breeding season to compete for mates and continue to migrate in search of fresh habitat. Bison are an integral part of the complex Greater Yellowstone ecosystem, exposed to natural predation and extreme environmental conditions.


Bison are a migratory species, and are not restricted by Yellowstone’s boundaries. Suitable habitat and public tolerance outside the park, however, are limitations to proper management. The NPS, along with other federal, state, and tribal agencies are developing policies for bison access to winter range outside Yellowstone.

In 2000, the NPS and the state of Montana created the Interagency Bison Management Plan (IBMP) to assess the challenge of the growing bison population migrating outside of Yellowstone’s boundaries. This original management plan called for a target population of around 3,000. However, the population has averaged around 4,000 individuals over the last decade. In July 2015, an estimated 4,900 bison in two subpopulations roamed across the Yellowstone landscape.

During the harsh winter, the herd ranges out of the park in search of food, causing human-bison conflict and fear of disease transmission between bison and cattle. Brucellosis, a livestock disease, has been detected in some wild bison. About 50% of the population tested positive for exposure to the disease, but were not infectious. Research indicates that about 15% of exposed female bison are infectious at the time of testing.

For the past 16 years, the NPS has been culling the population to mitigate these concerns. Culling methods include limited hunting outside the park and capturing bison near the park boundary and transferring them to Native American tribes for slaughter. The NPS plans to cull 600-900 bison in 2016, the highest number in over 8 years.


The NPS is studying the feasibility of using quarantine sites as an alternative location for surplus bison. The Fort Peck tribes of northern Montana have established a quarantine site ready to host surplus bison. Bison are historically an important part of Native American culture. Right now, it is illegal to move bison exposed to disease anywhere except a meat processing facility. From quarantine, bison that test negative for disease would be sent alive to other public, private or tribal lands for conservation, hunting or food production. However, this quarantine method will not entirely replace the need for capture or slaughter and will not change the hunting opportunities outside the park. The NPS is currently evaluating the use of such sites as a possible management solution.

Hunting inside Yellowstone is of course prohibited. The bison offer a huge recreational opportunity for wildlife viewing. Some people want to see the park opened to bison hunting. The NPS is adamantly opposed to that idea, stating hunting will change the behavior of wildlife and alter recreational experiences. The NPS is engaging the public in their decision making process. Several open house meetings and a public scoping comment period on the management plan were held in 2015.

The Interagency Bison Management Plan has effectively prevented disease transmission and maintained a viable population, but clearly needs revision to meet the challenges of a growing bison population. New disease data is available and public opinion is shifting toward more tolerance to bison in Montana. The NPS needs a new management strategy that accommodates larger herd size and allows bison to move more freely onto suitable public lands in the Greater Yellowstone ecosystem.

The North American bison is an icon of successful conservation and American wilderness. New strategies are being built that will hopefully lead to improved management of the species outside Yellowstone National Park.

For more information from the National Park Service on Yellowstone’s bison, check out these Q&A videos at


Twice a week, SCI Foundation informs readers about conservation initiatives happening worldwide and updates them on SCI Foundation’s news, projects and events. Tuesdays are dedicated to an Issue of the Week and Thursday’s Weekly Updates will provide an inside look into research and our other science-based conservation efforts. Like us on Facebook or follow us on Twitter and Instagram for more SCI Foundation news.

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