There are too many bison in Yellowstone National Park and plans are to remove more than 1,300 of the park’s famous “fluffy cows” from its boundaries over the winter.
The recommendation was published in a report by Chris Geremia, Yellowstone’s bison program manager
In the report, Geremia says there were nearly 6,000 bison in Yellowstone in August. Removing 1,375 bison will keep the herd within the population range of 3,500-6,000 animals established by the Interagency Bison Management Plan (IBMP).
“Total removal among partners and methods should reflect existing demographic conditions of 30% calves and yearlings, 70% adults, with an even sex ratio of 50% males and females,” the report says.
The IBMP uses three methods for removing Yellowstone bison. The collected animals will be available for state and tribal harvest outside the park, placed in the Bison Conservation Transfer Program or donated to the Tribal Food Transfer Program.
However, wildlife advocates believe the long-term ecology of Yellowstone’s bison management is being jeopardized by short-term decisions to cull the herds, which are perceived as political rather than scientific.
In fact, the Greater Yellowstone Ecosystem can support a bison population double what it has now, they say.
“In my opinion, we're interfering with evolution through this whole management program,” said ecologist, author and bison advocate George Wuerthner. “The long-term consequences are that we're domesticating Yellowstone's bison. And that, to me, is a real tragedy.”
Able Vs. Allowed
Wuerthner has worked in the Greater Yellowstone Ecosystem for decades and is president of the Montana Wild Bison Coalition.
His evaluation of the IBMP is Yellowstone and the National Park Service are doing what they can under the political pressures of several agencies and people outside the park.
Wuerthner said that the removal of bison under the auspices of the IBMP isn’t based on ecology. The National Park Service’s own studies determined that the GYE could easily support twice the 6,000 bison maximum it currently maintains.
“The NPS estimates that Yellowstone alone could support 10,000 bison,” he said. “If you were to add all national forests and other lands immediately adjacent to Yellowstone, you could get the population up to 12,000 to 15,000 bison. I'm not going to venture an estimate because it would depend upon how much of that adjacent land was available, and there's no doubt that you will have conflicts.”
Those “conflicts” would come from several places outside and in the federal government. Avoiding those potential clashes is, in Wuerthner’s opinion, the driving force behind Yellowstone’s bison management.
On July 24, the NPS announced “a decision about the future management of bison” in Yellowstone. Future management will prioritize transferring brucellosis-free bison to American Indian tribes, bison harvests “to the extent feasible” and “limited summer and winter habitat outside the park.”
“In 2024, the National Park Service issued a decision on bison management, setting a target population of 3,500–6,000 bison post-calving, with the goal of achieving objectives related to demographics, genetics, ecology, social considerations, and reducing the risk of brucellosis transmission through adaptive management,” Geremia wrote in his report.
Wuerthner said the decision and ongoing implementation of the IBMP is Yellowstone and the NPS doing what they are allowed to do with bison rather than what they could truly accomplish to create a stronger future for genetically diverse, free-roaming bison.
“The National Park Service is under political pressure from all angles,” he said. “From the secretary of interior to the senators In Montana to the livestock industry. It’s a very selective group that doesn't want to see bison on public lands.”
Bison And Bovines
One of the main factors driving bison management in Yellowstone is the spread of disease, the IBMP says.
Ranchers have been concerned about the spread of brucellosis from wild bison to domestic cattle for decades, which keeps bison confined to the park and far from any contact with livestock.
The spread of disease is a legitimate concern, Wuerthner said, adding that ranchers are targeting the wrong culprit. Bison isn’t the threat to ranchers that elk are, he said.
“One of the reasons there's such an emphasis in Montana against allowing bison to wander from Yellowstone is this fear of brucellosis transmission to cattle,” he said. “If cattle get brucellosis, they can abort their calves, and so the cattle industry doesn't want to see that happen widespread.
“But the funny — or not-so-funny — thing is that there's no documented case of that happening under natural conditions.”
A 2013 study by the Centers for Disease Control and Prevention showed that brucellosis was discovered in 13 beef cattle herds and four ranched bison herds in the Greater Yellowstone Area between 2002 and 2012.
However, the study found that the animal primarily responsible for the spread of brucellosis has been and is still freely roaming throughout the ecosystem. Unvaccinated cattle and bison got brucellosis in areas devoid of other bison, but with abundant elk.
Brucellosis is present in free-ranging bison and elk, and the NPS estimates that 60% of adult female bison in Yellowstone test positive for the bacteria, but only 10% to 15% of the population would be considered “infectious.”
Additionally, Geremia wrote that “there have been zero brucellosis transmissions from Yellowstone bison to cattle” in his 2024 report.
Wuerthner believes bison are being scapegoated for a threat coming primarily from free-ranging elk.
“What we have seen is dozens of livestock herds getting brucellosis from elk,” Wuerthner said. “We don't shoot the elk that wander out of Yellowstone. We don't capture and ship them away, but we're doing that for bison.”
Range Rage
If free-ranging bison were allowed to roam beyond the boundaries of Yellowstone, they would cross into the national forests immediately adjacent to the park.
This is where Wuerthner sees another reason why the park’s population is contained and kept below the higher threshold the ecosystem could support.
“Ranchers don't want to see bison in Custer Gallatin National Forest,” he said. “The forage is currently allotted to domestic livestock, and they realize that if push comes to shove, the public would demand that some of that forage go to bison. The livestock industry doesn't want to see that happen.”
Wuerthner believes this is another reason the main argument for bison management hinges on preventing the spread of brucellosis. Even if cattle are more likely to get the disease from elk, they don’t present the same kind of foraging competition as bison.
There is a brucellosis vaccine developed for cattle, although it’s not 100% effective at preventing the spread of the bacteria. Wuerthner believes the threat of brucellosis has been exaggerated, as opposed to the reality that it’s less dangerous now than ever.
“If you managed bison similarly to how we manage elk, we would probably have significantly more bison on public lands,” he said. “The problems that the bison may create can be dealt with on a case-by-case basis.
“But there's been this fear and something like a misinformation campaign making brucellosis sound like a threat to a whole state's livestock industry when it might only affect an individual rancher who gets it in their herd. But that’s not a threat to the industry.”
Yellowstone officials acknowledge that there is an effort to expand the range of its bison population, but that’s dependent on the permission of the agencies managing those areas.
“The 2024 bison management plan specifies that bison will be managed within available tolerance areas and within the published population ranges,” said Morgan Warthin, Yellowstone’s Chief of Public Affairs. “There is great interest from a variety of Tribes and conservation landscapes to receive Yellowstone bison. Larger distribution of bison would require state-authored increases in tolerance areas.”
Eventual Domestication
Beyond the political forces opposed to expanding Yellowstone’s bison numbers and range, there are also concerns about the long-term biological implications of bison management.
Bison might have recovered from the brink of extinction before, but Wuerthner still sees a species closer to the precipice than many realize.
“The bison in Yellowstone started from a very small herd of relic animals that were left over after the initial decades of the park's protection,” he said. “That small herd means that the bison in the park have gone through what's called a genetic bottleneck, and the genetic diversity within the herd is greatly reduced.”
One of Yellowstone’s goals through the IBMP is maintaining and expanding bison genetic diversity. Wuerthner applauds this commitment but believes its implementation is fundamentally and unavoidably flawed.
“We have a genetic problem here,” he said. “The removal of bison (through the IBMP) is not based on which individuals are ‘the least fit.’ They’re taking thousands of animals regardless of their age, fitness or breeding potential, and any animal that migrates out is getting shot or being captured.”
Wuerthner said migration is essential to bison's evolutionary success. Migration allowed bison herds to survive beyond the last Ice Age, but those instincts are gradually being lost due to ongoing management.
“The tendency to migrate differs among individuals,” he said. “The individuals that tend to migrate are going outside the park and getting shot. So, we're effectively reducing that tendency.”
That genetic bottleneck makes bison even more susceptible to disease. If an infection or bacteria that the bison were particularly susceptible to appeared in Yellowstone, the entire population could be lost.
In Wuerthner’s view, that is the long-term tragedy of current bison management: the gradual but inevitable “domestication” of bison.
“All of these things are, in effect, domesticating bison,” he said. “We're interfering with evolution through this management program. And the long-term consequences of this is that we're domesticating Yellowstone's bison.”
Yellowstone biologists aren't concerned about the genetic diversity of its bison, however.
DNA analysis conducted this year suggested there was healthy gene flow throughout the park’s population.
“In 2024, the NPS completed a scientific study analyzing nuclear and mitochondrial DNA from 282 bison sampled between 2019 and 2021,” Geremia wrote. “The study found evidence that bison form a single intermixing population. The average observed genetic diversity was consistent with estimates from the late 1990s. Bison with ancestry from both of the park’s original female founding populations were distributed across the park and its herds.”
Above And Beyond
Overall, Wuerthner doesn’t fault Yellowstone or the NPS’s implementation of the IBMP. However, since the park’s ecological goals are politically hampered, he and many other agencies and individuals are exploring different solutions to ensure the bison’s future success.
Colossal Biosciences recently announced an initiative to resurrect the lost genetic diversity of bison by recovering DNA from the bones and hides of long-dead bison that died or were killed before the genetic bottleneck. Meanwhile, Yellowstone Forever launched a campaign to expand a refuge and transfer area for bison to protect them from culling, harvesting, or hazing operations.
Between 2020 and 2024, more than 300 bison have been transferred from Yellowstone to tribal lands across the lower 48 states and Alaska through the Bison Conservation Transfer Program. These newly established herds are reestablishing bison throughout their historic range, which could help restore the ecosystems left behind by their near extinction.
Wuerthner applauds these efforts but feels these are adjacent to the core issue of mitigating the long-term impacts of bison management. He believes one of the best and easiest possibilities is getting more bison reestablished in more places.
“One solution would be to allow Yellowstone’s bison to utilize and colonize the national forests, BLM, and other public lands around the Yellowstone area,” he said. “That might mean more bison going over the mountains towards Cody and southward into the Teton Wilderness, but it would also mean allowing them on the Custer-Gallatin National Forest.”
Wuerthner would also like to see more places with free-ranging bison herds, like the three-million-acre Charles M Russell Wildlife Refuge in Montana, the second-largest National Wildlife Refuge in the lower 48. But there are other vast expanses where bison are currently absent but could thrive if reintroduced.
“Wyoming’s Red Desert would be a good place for bison,” he said. “It’s part of their historical landscape, the largest area without fences in Wyoming, and almost all its public land. The Green River-Red Desert area would be a great place to establish a wild bison herd.”
Special Status
One other potential solution could ensure better bison futures, a special designation for Yellowstone’s bison under the Endangered Species Act.
American bison are classified as “near threatened” on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Still, advocates say the Yellowstone population technically qualifies for more protection, which Wuerthner supports.
“Some people have suggested that the population in Yellowstone should be designated a distinct population segment and protected under the Endangered Species Act, which I would support,” Wuerthner said.
Even Yellowstone classified its various bison herds as a single population, though it hasn’t taken a stance on its conservation status.
“The population is best described as a metapopulation—a single population with sufficient gene flow across two relatively distinct breeding geographies. In 2024, the northern herd bred in the Lamar, Upper Lamar, Mirror Plateau, and Pelican Valleys, while the central herd bred in the Hayden Valley,” Geremia wrote.
Through the work of the National Park Service, tribal partners, and conservation groups like the Montana Wild Bison Coalition, Wuerthner sees possible solutions to address an urgent issue. The stakes are high, as the consequence is losing wild bison forever.
“There's only about 20,000 bison in the United States that you could say are really, truly wild,” he said. “Even though there are hundreds of thousands of bison in the West on ranches, tribal lands and state parks, they are managed like domestic livestock.
“I've talked to several conservation biology geneticists, and all of them said there should be more bison protected in Yellowstone and its surrounding lands. In other words, you could have a much larger number of bison in the Greater Yellowstone Ecosystem if they were permitted to wander outside Yellowstone National Park, and I believe there should be.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
