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The protection and recovery of bison in Yellowstone is one of the great triumphs of American conservation. This video explains why bison are controlled in Yellowstone.
Success & Controversy
The protection and recovery of bison in Yellowstone is one of the great triumphs of American conservation. In 1902, after years of market hunting and poaching, there were only about two dozen bison left in Yellowstone. Over the next 100+ years, park employees worked to bring this species back from the brink of extinction. We succeeded, and now face the challenge of helping to manage a healthy population of bison that sometimes roams beyond park borders onto private land and land managed by other agencies, where there is less tolerance for them.
Our bison management goals include: 1) preserve a viable population of wild, migratory bison; 2) work with Interagency Bison Management Plan (IBMP) partners to maintain human safety and a low risk of brucellosis transmission to cattle, and minimize property damage; and 3) honor the federal Indian trust responsibility.
We work to maintain a viable, wild, migratory population of our national mammal.
Yellowstone provides one of the few places where bison live much like their ancestors did: unfenced, and unprotected from harsh winters, drought, or predation. Yellowstone bison also provide a physical link to those ancestors. They were declared our national mammal in 2016 because they’re a symbol of wild America, an important part of our heritage, and a key player in an ecosystem that’s much larger than a national park.
We want to send Yellowstone bison to other conservation areas instead of slaughter.
In coordination with the Animal and Plant Health Inspection Service (APHIS) and their leased facility outside the park, the Bison Conservation Transfer Program supports the transfer of about 100 animals per year to Tribes as an alternative to slaughter. Recent scientific findings suggest that the time some animals spend in the program can be significantly reduced, which could increase the number of bison returned to Tribes each year.
We want to support hunting opportunities outside the park.
Right now, most hunting occurs adjacent to the park boundary, which prohibits bison from moving further into areas where they are tolerated. Yellowstone National Park wants to work with state partners and Tribal Nations to explore ways to safely improve hunting outside the park. Improving hunts would further reduce the number of animals sent to slaughter and help treat bison like other wildlife, such as elk.
Bison Conservation Transfer Program
During August 19-23, 2019, Yellowstone moved 55 bison to the Fort Peck Indian Reservation in northeastern Montana. It was the first direct relocation of bison to a new home as an alternative to slaughter and was the culmination of eight years of compromise between the federal government, state of Montana, and Fort Peck Assiniboine and Sioux Tribes. Those bison had been held in a quarantine facility in the park for 17 months and underwent rigorous testing to show they did not have a disease called brucellosis.
As bison migrate north out of the park, some are captured and entered in the Bison Conservation Transfer Program. Animals are then moved between facilities to undergo various testing phases. The first two testing phases are completed in Yellowstone quarantine facilities (Stephens Creek) or on private lands leased by APHIS near the northern park boundary. APHIS and Montana animal health officials certify bison as brucellosis-free at the completion of Phase 2, allowing their transfer across Montana to the Fort Peck Reservation, where bison complete Phase 3. Afterward, the Fort Peck Tribes transfer some bison to the InterTribal Buffalo Council, who distribute them to other Tribes across North America.
Expanding the Bison Conservation Transfer Program
Currently, there is not enough space for all the bison that qualify for the program. The first two phases of testing require that animals are held within state- and federal-approved quarantine facilities. There are currently two such facilities; one that is inside Yellowstone National Park and the other on private land leased by APHIS near the northern park boundary. In fall 2022, Yellowstone increased the 80-animal capacity of the Bison Conservation Transfer Program facility in the park to 200 animals. These upgrades, done in partnership with Yellowstone Forever and the Greater Yellowstone Coalition, coupled with continued coordination with APHIS (the APHIS leased facility has a capacity of 60 animals) will result in the transfer of about 100 animals per year to Tribes as an alternative to slaughter.
Many Tribes see Yellowstone bison as uniquely linked to their ancestral descendants because they were never completely extirpated from the park. To many Tribal members, returning bison to Tribal lands goes well beyond finding an alternative to slaughter. It is about restoring a part of themselves that is missing.
What You Can Do
We encourage you to learn more about bison conservation. Read about the history of bison management, read our questions and answers below, download a copy of Yellowstone Bison: Conserving an American Icon in Modern Society, read our latest annual Bison Conservation Update, and view the grazing issue of Yellowstone Science.
Questions & Answers
Five federal/state agencies and three Tribal entities make decisions about Yellowstone bison in a cooperative effort called the Interagency Bison Management Plan (IBMP). These include the Animal and Plant Health Inspection Service, the Confederated Salish & Kootenai Tribes, the InterTribal Buffalo Council, Montana Department of Livestock, Montana Fish, Wildlife & Parks, the National Park Service (Yellowstone National Park), the Nez Perce Tribe, and the US Forest Service (Custer-Gallatin National Forest).
A total of 50 bison were removed during the 2021/2022 winter, which was below the range of 600 to 1,100 agreed to by managers. Removals included 13 bison harvested outside the park in Montana; 27 captured at the Stephens Creek facility and sent to slaughter; and 10 entered the Bison Conservation Transfer Program.
The NPS no longer sets a bison removal target. As the population has increased over time, IBMP partners have met the goals of preserving a wild population while minimizing the chance that bison transmit brucellosis to livestock. The current population of 5,900 animals is within an acceptable range. The NPS may capture bison in order to: 1) enter up to 250 new animals into the Bison Conservation Transfer Program during the 2022/2023 winter; or 2) if necessary, lower the number of bison exiting the park to reduce conflicts. Bison that do not qualify for live transfer may be transferred to American Indian Tribes for slaughter and distribution of meat and hides to their members.
Yes. Yellowstone’s bison population has grown steadily over the last 50 years: from 500 animals in 1970 to nearly 6,000 in 2022. Yellowstone bison represent a unique source of genetic diversity.
No: that designation did not provide any special protection to bison. Read more about the National Bison Legacy Act.
Bison migrate to lower elevations where food is more available (less snow) just like bighorn sheep, elk, mule deer, pronghorn, and many other animals. They return to the park’s higher elevation grasslands to feed during summer.
Bison are not allowed to move freely outside Yellowstone due to fears they might transmit brucellosis to cattle, and out of concerns about competition with cattle for grass, human safety, and property damage. Elk are also infected with brucellosis, but their movements outside the park are not restricted. State governments control the management of wildlife outside Yellowstone (unless a species is federally listed as threatened or endangered).
Outside Yellowstone, states manage wildlife and Yellowstone cannot force them to tolerate more migrating bison.
Yellowstone isn't big enough to manage a migratory species like bison on its own. Bison conservation is a shared responsibility that crosses many political boundaries. Withdrawing from the IBMP would make it more difficult to collaborate with the land management agencies and Tribes that share an interest in what happens to bison when they leave the park. Additionally, Yellowstone’s superintendent is not the signatory of the original IBMP. The agreement was signed and approved by the Secretary of the Interior, who would need to make any decision about withdrawing.
On behalf of the IBMP, bison are captured near the north boundary of Yellowstone as they migrate out of the park. Fences guide them into enclosures, so they wander in on their own or are sometimes guided in by riders on horseback. For more information on the capture and shipment process, browse photos on our Flickr.
We transfer captured bison to Tribes who transport them to slaughterhouses for processing.
Tribal Nations distribute the bison meat and hides to their members.
No: we receive no payment for bison shipped from our capture facility.
No. The safety of people and animals is our top priority at Stephens Creek. The Humane Society has evaluated the operation twice, and each time we've adopted their recommendations. During 2020, we received expert training and worked to improve low-stress handling of bison during handling and processing. Two old photos are often used to falsely depict our handling practices at Stephens Creek. One shows a bison being held with a nose ring during brucellosis testing, a practice we haven’t used in many years (we now have a hydraulic chute that holds the animals relatively still during testing). The second shows a bison being carried by a front-end loader: a photo that was taken outside the park, most likely after a bison was shot by a hunter or hit by a car. Adult bison can be very large and heavy and often times require heavy equipment to move carcasses from vehicle accident scenes. For a detailed view of the capture and shipment process, browse photos on our Flickr.
No. Yellowstone’s bison population has grown steadily over the last 45 years: from 500 animals in 1970 to nearly 6,000 in 2022. Each year, the bison population in the park increases by 10%-17%. Along with elk, bison are the most numerous large mammals in Yellowstone, and periodic culling will not alter that fact. The sizes of most wild ungulate populations in North America are limited by hunting and/or captures and removals.
We are legally obligated to follow the directives of the IBMP. Each member of the IBMP has a different perspective on the conservation of wild bison, so conflict resolution is an integral part of the management strategy. We would like to reduce the shipment of bison to slaughter and have implemented the Bison Conservation Transfer Program to reduce numbers slaughtered.
Yes. People both understate and overstate the risk of brucellosis transmission. Transmission of brucellosis from bison to livestock is possible because in late winter, bison migrate to low elevation areas outside the park where livestock are concentrated. At this time, bison are late in their pregnancy: the most probable time for infected animals to abort fetuses that might be found by other animals. The fact that there's never been a documented transmission of brucellosis from Yellowstone bison to cattle does not mean it couldn't happen. Rather, it’s a testament to the diligent management efforts put forth by the state of Montana and the National Park Service to prevent commingling of bison and cattle during the time period when transmission is most likely.
Yes. Over the last two decades, more than 20 livestock operators in the three states surrounding Yellowstone discovered brucellosis in their animals. In each case, wild elk transmitted the disease.
They do, but there is no vaccine that is 100% effective at reducing abortions due to brucellosis or eliminating the potential of infection from wildlife.
The NPS initiated the Bison Conservation Transfer Program to identify bison that don't have brucellosis and transfer them to new areas as an alternative to sending them to slaughter. Since 2019, nearly 300 bison have been transferred to the Fort Peck Assiniboine and Sioux Tribes. Of those, roughly 170 were transferred to the InterTribal Buffalo Council and given to about 23 other member Tribes across 12 states. Continued coordination with APHIS will result in transferring about 100 animals per year to Tribes as an alternative to slaughter.
In the history of North America, only humans, disease, predation, and starvation have successfully controlled bison numbers. Hunting outside the park is the preferred method for controlling the population today, but bison need greater access to land to disperse beyond our boundaries and pioneer new areas. Currently, the area where bison can be hunted is very small, and bison often respond to the hunting pressure by returning to the security of the national park (where hunting is prohibited). In addition, the NPS initiated the Bison Conservation Transfer Program to identify bison that don't have brucellosis and transfer them to new areas as an alternative to sending them to slaughter. Since 2019, nearly 300 bison have been transferred to the Assiniboine and Sioux Tribes of the Fort Peck Indian Reservation. Of those, roughly 170 were transferred to the InterTribal Buffalo Council and given to about 23 other Tribes across 12 states. Continued coordination with APHIS will result in transferring about 100 animals per year to Tribes as an alternative to slaughter.
Right now, it’s against state and federal laws to move wild bison exposed to brucellosis anywhere except to meat processing and research facilities. The NPS has initiated the Bison Conservation Transfer Program to identify bison that do not have brucellosis and transfer them to new areas as an alternative to sending them to slaughter.
Some captured bison that test negative for brucellosis exposure are moved into double-fenced pastures and held until they all test negative for two to three consecutive months. Any animals that convert to testing positive are removed and shipped to slaughter. The remainder of the bison then undergo additional testing for brucellosis with timelines and criteria that vary by age and sex. At the end of this testing protocol, APHIS and state of Montana animal health officials certify the bison as brucellosis-free. This certification allows their transfer across the state of Montana to the Fort Peck Indian Reservation. Bison complete one year of assurance testing at the Fort Peck Indian Reservation, after which the Fort Peck Assiniboine and Sioux Tribes transfer some bison to the InterTribal Buffalo Council who distribute them to member Tribes throughout North America.
This program reduces the need for capture/slaughter operations and promotes the restoration of plains bison to suitable areas of the country.
To date, hunting outside the park has been ineffective at limiting bison numbers. The area where bison can be hunted is very small, and bison often respond to concentrated hunting pressure along the park boundary by returning to the security of the national park where hunting is prohibited. For hunting to become more effective, bison need greater access to public lands outside the park, like wild elk and other animals, so they can disperse beyond our boundaries and pioneer new areas.
Federal law (National Park Protection Act, 1894) prohibits hunting in Yellowstone. Because of this prohibition, Yellowstone offers some of the best wildlife viewing opportunities in the world. This prohibition also supports our goal to manage the park so that human activities have as little effect on natural processes as possible. Allowing hunting in Yellowstone would drastically affect the behavior of animals and change the experience for people who come to watch them.
No fertility control methods that are affordable, easily delivered, highly effective, and reversible are currently available for delivery to wild bison spread across a vast landscape. Fertility control could have unintended, adverse effects on the bison population in Yellowstone.
From Dozens to Thousands
A history of bison management in Yellowstone.
Bison Engineering a Better Yellowstone
Learn more about how bison impact the Yellowstone ecosystem.
Last updated: August 9, 2023