Yellowstone Bison

A herd of adult bison and calves walk from a sagebrush covered hillside
The bison is the largest land mammal in North America. Bulls are more massive in appearance than cows, and more bearded. For their size, bison are agile and quick, capable of speeds in excess of 30 mph. Each year, bison injure park visitors who approach too closely.

NPS / Neal Herbert


Yellowstone is the only place in the United States where bison (Bison bison) have lived continuously since prehistoric times. Yellowstone bison are exceptional because they comprise the nation’s largest bison population on public land and are among the few bison herds that have not been hybridized through interbreeding with cattle. Unlike most other herds, this population has thousands of individuals that are allowed to roam relatively freely over the expansive landscape of Yellowstone National Park and some nearby areas of Montana. They also exhibit wild behavior like their ancient ancestors, congregating during the breeding season to compete for mates, as well as migration and exploration that result in the use of new habitat areas. These behaviors have enabled the successful restoration of a population that was on the brink of extinction just over a century ago.

However, some Yellowstone bison are infected with brucellosis, a livestock disease that can be transmitted to wild bison and elk as well as cattle through contact with infected fetal tissue. To prevent conflicts with ranching and other activities outside the park, the National Park Service works with other federal, state, and tribal agencies to manage and develop policies for bison access to winter range outside the boundaries. Conservation of wild bison is one of the most heated and complex of Yellowstone’s resource issues. All of the interested parties bring their own wide-ranging values and objectives to the debate. Continue: Description, Migration, and Habitat


Quick Facts

Number in Yellowstone

Estimated at 4,900 in July 2015. This includes two sub-populations in Yellowstone: northern (3,600) and central (1,300).

Where to See

  • Year-round: Hayden and Lamar valleys.
  • Summer: grasslands.
  • Winter: hydrothermal areas and along the Madison River. Blacktail ponds, Mammoth and Tower areas.

Size and Behavior

  • Male (bull) weighs up to 2,000 pounds, female (cow) weighs up to 1,000 pounds.
  • May live 12­–15 years, a few live as long as 20 years.
  • Feed primarily on grasses and sedges.
  • Mate in late July through August; give birth to one calf in late April or May.
  • Can be aggressive, are agile, and can run up to 30 miles per hour.


  • Yellowstone is the only place in the lower 48 states to have a continuously free-ranging bison population since prehistoric times.
  • In the 1800s, market hunting, sport hunting, and the US Army nearly caused the extinction of the bison.
  • By 1902, poachers reduced Yellowstone’s small herd to about two dozen animals. The US Army, who administered Yellowstone then, protected these bison from further poaching.
  • Bison from private herds augmented the native herd.
  • For decades, bison were intensively managed due to belief that they, along with elk and pronghorn, were over-grazing the park.
  • By 1968, intensive manipulative management (including herd reductions) of bison ceased.

Contact the Park

Mailing Address:

P.O. Box 168
Yellowstone National Park, WY 82190-0168


(307) 344-7381
Recorded information. For road and weather information, please dial 307-344-2117.

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