Bison are considered a keystone species: they once roamed the continent in great herds, and their grazing pressure helped shape the ecology of the Great Plains.
© Midori Layzell
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.
Historically, bison numbered an estimated 20-30 million. Unregulated shooting of bison, which culminated in mass slaughters during the 1870s, reduced the population to 1,091 in 1889. Today, approximately 500,000 bison live across North America. Most are not pure bison but rather have been cross-bred with cattle in the past and are raised as livestock on ranches. Fewer than 30,000 bison are in conservation herds, and fewer than 5,000 are free-ranging and disease-free.
Range
Bison once roamed across much of North America. Today bison are ecologically extinct 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 free-roaming plains bison (about 4,000), and Wood Buffalo National Park has the largest population of free-roaming wood bison (about 10,000).
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.
Bison move continuously as they eat so that they rarely overgraze an area. They historically roamed great distances. 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 often rub, roll and wallow. Wallowing creates a saucer-like depression called a wallow. This was once a common feature of the plains; usually these wallows are dust bowls without any vegetation. In winter, bison can dig through deep snow with their heads to reach the vegetation below.
Bison have poor eyesight, but have acute hearing and an excellent sense of smell. They can reach speeds of up to 35 mph.
Reproduction
Mating Season: June-September, peak activity in July-August.
Gestation: 270-285 days. Calf is born April-May.
Litter size: 1 calf.