American bison are not officially listed as endangered under U.S. law, but they remain a conservation-dependent species that came within a few hundred animals of total extinction. From an estimated 30 to 60 million individuals before European settlement, the population crashed to fewer than 1,000 by the 1890s. Today, roughly 20,500 bison live in conservation herds, while about 420,000 exist in commercial production, essentially managed as livestock. That distinction matters: the species survives in large numbers, but truly wild, free-ranging bison occupy a tiny fraction of their former range and face ongoing threats that keep their long-term future uncertain.
The 19th-Century Slaughter
The near-extinction of bison was fast and deliberate. The westward expansion of European settlers in the 1800s drove the collapse, but it was industrialized killing that made it catastrophic. Railways opened the plains to commercial hunters, repeating rifles made mass killing efficient, and an international market for buffalo hides created enormous financial incentive. The period from roughly 1820 to 1880, known as the Great Slaughter, reduced the population from tens of millions to near zero.
Hunting alone doesn’t explain the full picture. The U.S. military actively encouraged the destruction of bison herds as a strategy to control and displace Indigenous peoples, who depended on the animals for food, shelter, and culture. At the same time, cattle brought diseases like brucellosis into bison territory, droughts stressed the grasslands, and domestic livestock (horses, cattle, and sheep) competed directly for forage. By some estimates, as few as 300 bison survived at the population’s absolute lowest point.
Why Recovery Numbers Are Misleading
The headline figure of 420,000 bison in the U.S. sounds like a success story, but the vast majority of those animals are in commercial herds raised for meat. They’re fenced, selectively bred, and managed like cattle. Conservation herds, the ones managed for ecological and genetic health, total only about 20,500 animals scattered across public lands, tribal territories, and nonprofit preserves. That’s a meaningful recovery from the 1890s, but it represents less than 0.1% of the species’ pre-colonial population.
The U.S. Fish and Wildlife Service has the Yellowstone bison population under review for potential listing under the Endangered Species Act. A 2019 petition to list them was initially found “not substantial,” but a 2022 review of three newer petitions concluded that listing may be warranted, and a formal status review is underway. The species is included in the agency’s national listing workplan through 2027. Meanwhile, the IUCN’s Bison Specialist Group is finalizing an updated Red List assessment for publication in 2025, developing new criteria for determining which bison subpopulations qualify as truly “wild.”
Cattle DNA in Every Herd
One of the less visible threats to bison is hybridization with domestic cattle. During the late 1800s and early 1900s, ranchers crossbred the last surviving bison with cattle in attempts to create hardier livestock. That genetic legacy persists. A 2022 genomic study published in Scientific Reports tested bison from herds long considered genetically pure, including Yellowstone, Wind Cave, and Elk Island National Parks, and found cattle DNA in every single animal tested.
The levels are low. The cleanest individual carried about 0.24% cattle ancestry, while the highest was 2.45%. Researchers found cattle-origin DNA segments scattered across bison genomes in varying sizes and frequencies, but no animal was completely free of them. The practical effect on bison biology is likely minimal at such low percentages, but the finding reshapes conservation priorities. Rather than dividing herds into “pure” and “impure” categories, scientists now argue for a more inclusive, species-wide approach to conservation that accepts low-level cattle introgression as a reality across the entire species.
Disease Keeps Bison Fenced In
Brucellosis, a bacterial disease that causes miscarriage in pregnant animals and reduced fertility, is one of the biggest practical barriers to expanding bison range. Bison in the Greater Yellowstone area carry the disease, and cattle ranchers fear transmission to their livestock. That fear drives aggressive management policies: bison that wander outside park boundaries are routinely hazed back or killed to prevent contact with cattle.
The disease creates a political and economic conflict that constrains where bison can live. Ranchers face real financial consequences from brucellosis outbreaks, including quarantines and lost livestock. As a result, bison are effectively confined to designated areas rather than allowed to roam freely across the grasslands they once dominated. This confinement limits genetic exchange between herds, restricts access to seasonal forage, and prevents the kind of large-scale migration that shaped bison ecology for millennia.
Fences, Highways, and Social Resistance
Even without disease concerns, bison face physical and political barriers to reclaiming their historical range. Research on rewilding efforts in the Canadian prairies found that the main obstacles are social acceptance and material resources, not ecology. Ranchers worry about property damage and competition with cattle. Fences, highways, railways, and cropland have carved the Great Plains into fragments that can’t support large migrating herds. Unlike deer or elk, bison are massive animals that can damage fences and pose perceived safety risks, making neighboring landowners resistant to restoration projects.
The result is that most conservation herds exist as small, isolated populations on islands of protected land. Without corridors connecting them, these herds can’t exchange individuals naturally, which limits genetic diversity and makes each population more vulnerable to local disasters like drought or disease outbreaks.
Climate Change and Forage Quality
Rising temperatures and intensifying droughts add a newer layer of stress. Research tracking bison movements found that the animals are highly sensitive to heat. Movement rates increase steadily as temperatures climb from extreme cold up to about 28°C (82°F), likely because the animals are tracking improvements in forage quality as grasses grow. But above that threshold, movement drops sharply, declining nearly 49% for every additional 10°C increase. At temperatures above 39°C (102°F), bison seek out shaded riparian areas and essentially stop foraging across the landscape.
Drought compounds the problem. When soils dry deeply, plant growth slows and forage quality declines across large areas. Bison in severe drought conditions move greater distances searching for food and water, burning more energy to meet basic nutritional needs. As climate change brings more frequent heat waves and deeper droughts to the Great Plains, the carrying capacity of bison habitat will shrink, putting additional pressure on already small and isolated herds.
Tribal-Led Restoration Efforts
One of the most significant recovery efforts is being led by Indigenous nations. The InterTribal Buffalo Council, working with The Nature Conservancy, has returned over 1,300 bison to tribal lands since 2020, with hundreds more transfers planned. These programs serve both ecological and cultural goals, reconnecting tribes with an animal that was central to their way of life before colonization deliberately severed that relationship.
Tribal herds are managed differently from commercial operations, with greater emphasis on natural behavior, genetic health, and landscape-scale grazing. Because many tribal lands are large and relatively unfragmented, they offer some of the best remaining opportunities for bison to live in conditions closer to their evolutionary norm. These efforts are expanding the species’ conservation footprint in ways that federal land management alone has not achieved.