Bison
Bison bison
The bison is a member of the bovine family. Commonly called “buffalo” (which is actually a different species not found in North America), it is the largest land mammal in North America. There are two subspecies: the wood bison in northern Canada and the plains bison which once roamed across much of the continent. The bison has a large head with relatively small, curving horns. Its dark brown coat is long and shaggy on the forequarters, including the front legs, neck, and shoulders, while the rest of the body has shorter, finer hair.
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.
Height 6-6.5 feet at the shoulder
Length 10-12.5 feet
Weight 900-2,000
lbs; males are larger than females
Lifespan 18-22 years in the wild; over 30 years in captivity
Diet
Staples grasses and sedges
Population
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
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 wallow 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. Bison 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.
Threats
Cross breeding with cattle threatens the genetic purity of bison. The few remaining genetically pure wild bison must be conserved separate from cross-bred bison to protect pure bison genes.
Today, the bison of Yellowstone National Park also face the threat of slaughter when they cross park boundaries and enter the state of Montana. The Montana Department of Agriculture fears the contamination of cattle by bison carrying the disease brucellosis, although there are no known cases of brucellosis passed by bison to domestic cattle in the wild.
Legal Status/Protection
* CITES Appendix II (wood bison only; plains bison have no protection)
* Convention on International Trade in Endangered Species of Wild Fauna and Flora, an international treaty with 172 member countries. Appendix I listed species cannot be traded commercially. Appendix II listed species can be traded commercially only if it does not harm their survival.
How You Can Help
- Help bison and other wildlife by adopting a bison at our Wildlife Adoption Center.
- Take Action for Wildlife at our Wildlife Action Center.
For additional information
Visit Defenders' Imperiled Species: Bison pages for more information about what Defenders is doing to help.
Wind Cave National Park
Wildlife Conservation Society
