American Bison



The “home where the buffalo roam” is the Western prairie, and these herds have historically roamed great distances. Today, home ranges are much smaller, about 10 square miles in summer and 40 square miles in winter. Bison herds are composed of related females and their young; adult males typically travel alone or in small groups. During migration or when food is plentiful, a bison herd can be hundreds-strong. Otherwise, males and females come together only during the mating season.

Bison are most active in early morning and late afternoon. In the midday heat, they rest, chew their cud, or wallow in the dust to rid themselves of parasites. The bison wallow—usually a dust bowl with no vegetation—was once a common feature of the plains. Bison herds have helped shaped the prairie ecosystem in many ways.


The American bison is an herbivore, feeding mostly on grasses, sedges, and forbs. Herds help to keep grasslands healthy as they graze on meadow sedges, trample weeds, and help prune plants. Since they move continuously while eating, they rarely overgraze an area. Their intensive and sporadic grazing also supports a healthy landscape for many other American wildlife species.

Life Cycle

Bison “cows,” or females, give birth in the spring to calves with orangey-brown fur. Mothers are very protective of their young. The big babies can weigh up to 66 pounds at birth and are able to run after three hours. Bison calves nurse for up to a year and reach adult size by age six. They can live up to 40 years.

Some of My Neighbors

Snowy Owls, Mountain Plovers, Black-Footed Ferrets, Prairie Dogs, Ground Squirrels

Population Status & Threats

The bison is classified as lower risk/conservation dependent, which means that it does not face an immediate threat of population reduction but is still dependent on conservation programs for protection. Bison used to be found throughout the U.S. from Washington State to Arizona, east to Florida, north to Massachusetts, and in all places between. Their range also extended into Mexico. An estimated 50 million bison roamed our continent when it was first settled by Europeans. By the turn of the century, westward expansion and excessive sport hunting in the nineteenth century—which culminated in mass slaughters during the 1870s—brought the species to the brink of extinction.

WCS Conservation Efforts

In 1907, 15 Bronx Zoo bison boarded railway cars and wagon trains headed for Oklahoma’s Wichita Mountain Preserve. These early pioneers were charged with an historic mission: to help the American bison recover on the Western Plains. The founders of WCS created the American Bison Society (ABS) to restore this national icon, and they did: Today, 20,000 wild bison roam the Western Plains. The herds of Yellowstone and other national parks still share a family tree with those at the Bronx and Queens Zoos. Today, WCS has begun a new chapter in the history of the ABS to restore the wild landscape that enables bison to roam freely. Conservationists hope that such ecological recovery will also increase other populations of American wildlife, such as black-footed ferrets and prairie dogs.

Learn more about the American Bison Society.