American bison

Class: Mammalia
Order: Artiodactyla
Family: Bovidae
Genus and Species: Bison bison
  • large hoofed animal with short curved horns and brown fur
  • large hoofed animal with short curved horns and brown fur
  • large hoofed animal with short curved horns
  • large hoofed animal with short curved horns and brown fur
  • large hoofed animal with short horns and molting fur
Share this page:

American bison

The largest terrestrial animals in North America, bison once roamed in herds numbering in the millions dominating prairie and forest ecosystems. Now reduced to a fraction of their current range and population, bison survive mainly in conservation herds.

Physical Description

The largest terrestrial animals in North America, bison are characterized by a hump over the front shoulders and slimmer hindquarters. Both male and female bison have a single set of short, sharply pointed, hollow horns that curve outward and up from the sides of the massive head. The head, neck, forelegs, and front parts of the body have a thick coat of long, dark hair. The adult bull adds to this thick coat with a black beard about one foot long. The rear part of the body is covered with much shorter hair. The shaggy head is the most heavily insulated part of their body, which has adapted as such to withstand blizzards as the animal stands facing into the wind. Heavy coats are shed in the spring as the animals roll to loosen the hair, which falls off in gobs.

Size

A mature bull can reach 5.5 to 6.5 feet (1.9 meters) high at the hump and nine to 12.5 feet (2.7 to 3.8 meters) in length. Females are normally smaller, at 7 to 10 feet in length (2.2 to 3.2 meters) and 5 feet high at the hump (1.5 meters). Bison can weigh 1,800 to 2,400 pounds (816 to 1,088 kilograms).

Native Habitat

At one time, bison were widespread from Alaska to northern Mexico, but the current range occupied by conservation herds has diminished to one percent of its original status.

Today, herds can be found in parts of Alberta, British Columbia, Manitoba, Northwest Territories, Ontario and Saskatchewan in Canada, as well as Arizona, California, Idaho, Montana, South Dakota, Utah, Alaska and possibly Texas in the United States. Modern conservation herds are substantially fragmented.

Originally, bison were found primarily in the grasslands and prairie of North America. Today, bison distribution is greatly limited due to population decline and their movements are greatly regulated. Within the national parks, bison are found at all elevations.

Communication

Bison communicate through grunts to maintain contact with each other, and will snort to warn intruders. Male bison display their fitness by charging and butting heads with other bulls. They also bellow hoarsely, lower their heads, and paw the earth defiantly, but they rarely fight to the death.

They have an excellent sense of hearing and smell, but cannot see very well, so an entire herd can stampede if it is startled. Bison have cloven hoofs, and can reach speeds of 30 miles per hour.

Food/Eating Habits

Bison are year round grazers. They feed primarily on grasses, but will also consume flowering plants, lichens and woody plant leaves depending upon availability. To find grass in winter they sweep their heads from side to side to clear the snow. On the average, bison ingest 1.6 percent of their body mass per day of dry vegetation. Bison require water every day as well.

At the Smithsonian's National Zoo, bison consume a diet of orchard grass hay and herbivore pellets.

Social Structure

Bison are usually found in bands arranged by sex, age, season, and habitat. Older bulls are often solitary. Both cows and bulls live in a dominance hierarchy, which is established early in life. Most of the year, females with young form small bands, and immature bulls may stay with them. The bands may congregate in large herds in the spring or fall to search for food or water. Mature males have their own groups that may reach up to 30 individuals. Grazing takes place during several periods each day and is conducted in loose groups. When bison travel, they form a line. Bison are also adept swimmers, able to cross streams and rivers without difficulty.

Reproduction and Development

Females are sexually mature at 2 to 3 years of age. While males reach maturity around age three, they generally do not breed until six years of age. Mating season runs from late June through September, and gestation can last around 285 days. Breeding bulls will protect their chosen females and, with little time to eat, may lose more than 200 pounds during the breeding season. A single yellow-red calf will be born away from the herd in a secluded area. After a few days, the calf can keep up with the herd and follows its mother until the following spring. Calves are nursed for seven to eight months and are fully weaned by the end of the first year.

Sleep Habits

They prefer to graze in the morning, rest, ruminate (chew cud) in the middle of the day and then graze again in the evening. Bison wallow in the dust and mud to keep cool and to sooth irritating insect bites.

Lifespan

The life expectancy of American bison is 15 to 20 years. Adult bison are relatively safe from natural predators; however, weak, old or young bison may fall prey to mountain lions, bears or wolves.

Before 1800, bison roamed the Great Plains in vast numbers; estimates range from 30 to 100 million. While most were west of the Mississippi ranging to the Rocky Mountains, some were found east of the river in forested areas. Bison were once a major source of meat and hides in the United States; they formed the basis of the economy for a number of Native American tribes. However, by the 1890s, there were fewer than 1,000 of these animals left on the continent. The U.S. government slaughtered many bison in an organized effort to destroy the livelihood of Plains Indians.

Conservation threats to American bison include habitat loss, hybridization in managed populations, and low genetic diversity among individual herds.

While bison have made a comeback since their population was devastated over 100 years ago, the species is still heavily dependent on conservation action for survival. Of the remaining American bison population, approximately 500,000 individuals are managed as livestock by private commercial ventures, while conservation herds are comprised of around 30,000 individuals. According to IUCN Red List guidelines, commercial herds are not eligible for inclusion in the IUCN's scope of wildlife conservation, so the IUCN status of bison reflects only those found in the 65 known free-ranging or partially-free-ranging herds.

Buffalo are Old World animals (Cape buffalo, water buffalo) and bison are only found in Europe and the United States. The taxonomy of bison has been under debate, and through DNA analysis it was determined that the two American subspecies—plains bison (Bos bison bison) and wood bison (Bos bison athabascae) are the same species. Many biologists have seen evidence that supports including the European bison, Bos bonasus, as the same species as the American bison. If proven true, this would have major conservation implications.

Wilma and Zora came to the Zoo from the American Prairie Reserve in northeastern Montana. Founded in 2001, American Prairie Reserve aims to create and manage a prairie-based wildlife reserve that, when combined with public lands already devoted to wildlife, will protect a unique natural habitat, provide lasting economic benefits and improve public access to and enjoyment of the prairie landscape. The reserve spans more than 300,000 acres of public and private land that is open to modern-day explorers for camping and recreation. The landscape is one of the most intact prairies left in North America and is home to hundreds of species, including elk, pronghorn, sage grouse, prairie dogs and a growing bison herd. Close neighbors of the American Prairie Reserve are the Fort Belknap and Fort Peck Indian communities.

Wilma and Zora got their names thanks to the students at two DC Universities -- Howard University and Gallaudet University.

Both schools have the bison as their mascot so the National Zoo invited students at each university to help selecting a name for the unnamed bison—an opportunity to connect to an iconic American animal for our nation, the conservation movement, as well as their alma mater.

Howard University students chose to name one bison “Zora” in honor of alumnus Zora Neale Hurston, acclaimed author, poet and civil rights activist. 

Students at Gallaudet University selected the name “Wilma” in honor of alumnus Wilma Newhoudt-Druchen, the first deaf woman elected to serve in the Republic of South Africa’s parliament. Meet the bison in this video!