Fact Sheet
Bison

Basic Facts About Bison

Millions of bison once thundered across North America. These massive animals, characterized by their long, shaggy brown coats, have poor eyesight but acute hearing and an excellent sense of smell.

Historically, the American bison played an essential role in shaping the ecology of the Great Plains. They graze heavily on native grasses and disturb the soil with their hooves, allowing many plant and animal species to flourish. Prairie dogs prefer areas grazed by bison where the grass is short so they can keep a lookout for hungry predators, and wolves once relied on bison herds as a major food source. Today, wild bison are making a small comeback in a few scattered places, but they need more room to roam.

Diet

Bison mainly eat grasses and sedges. 

Population

Did You Know?

The trails carved by animals like bison and deer in their seasonal migrations formed some of the earliest traceable paths into the American wildnerness, and were followed by Native Americans, explorers and pioneers.

An estimated 20 to 30 million bison once dominated the North American landscape from the Appalachians to the Rockies, from the Gulf Coast to Alaska. Habitat loss and unregulated shooting reduced the population to just 1,091 by 1889. Today, approximately 500,000 bison live across North America. However, most of these are not pure wild bison, but have been cross-bred with cattle in the past, and are semi-domesticated after being raised as livestock for many generations on ranches. Fewer than 30,000 wild bison are in conservation herds and fewer than 5,000 are unfenced and disease-free.

Range & Habitat

Though bison once roamed across much of North America, today they are “ecologically extinct” as a wild species throughout most of their historic range, except for a few national parks and other small wildlife areas. Yellowstone National Park has the largest population of wild plains bison (about 4,000), and Wood Buffalo National Park has the largest population of wild wood bison (about 10,000). With help from Defenders, two small herds of pure, wild Yellowstone bison were recently reintroduced to Fort Peck and Fort Belknap Indian Reservations.

Behavior

Did You Know?

A bison's thick fur offers great protection against the harsh elements of the American plains. Their winter coat is so thick and well insulated that snow can cover their backs without melting.

Known for roaming great distances, bison move continuously as they eat. The females, or cows, lead family groups. Bulls remain solitary or in small groups for most of the year, but rejoin the group during mating season.

Bison are adapted to the extreme weather conditions of the Great Plains, from summer heat to winter cold and blizzards. In winter, bison can dig through deep snow with their heads to reach the vegetation below.

Bison often rub, roll and wallow. Wallowing creates a saucer-like depression in the earth called a wallow. This was once a common feature of the plains; usually these wallows are dust bowls without any vegetation.

Reproduction

Bulls and cows do not mingle until breeding season. Dominant bulls “tend” to cows, following the cow around until the cow chooses to mate. During this period, the bull blocks the cow’s vision so that she may not see other competing bulls, and bellows at males striving for the cow’s attention.

Mating Season: June-September, peak activity in July-August
Gestation: 270-285 days.  Calf is born April-May.
Litter size: 1 calf

More on Bison: Threats to Bison »

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Bison with calf, © Diana LeVasseur
Success Story
November 2014 - More than 100 wild bison were brought to Fort Peck Indian Reservation, adding to this historic conservation herd.
Success Story
On March 19, 2012, about 60 genetically pure bison were relocated from a quarantine facility outside Yellowstone National Park to the Fort Peck Indian Reservation in eastern Montana.
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