Bison Background and Recovery

Commonly called “buffalo” (which is actually a different species not found in North America), the bison is the largest land mammal in North America. Bison are considered a keystone species; they once roamed the continent in great herds, and their grazing pressure helped shape the ecology of North America’s Great Plains.

Two subspecies exist: the wood bison and the plains bison. Bison were hunted to near-extinction in the 1800s. Today bison are making a comeback, but significant hurdles remain. Defenders is working to help restore wild bison to Indian Reservations, National Parks and National Wildlife Refuges.

Description

Bison can grow to over 6 feet at the shoulder, weight up to 2,000 pounds and reach speeds of up to 35 mph. They eat grass, moving continuously as they eat so that they rarely overgraze an area. They live 18 to 22 years in the wild. 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. In winter, bison can dig through deep snow with their heads to reach the vegetation below.

Habitat and Range

Bison once roamed across much of North America in great herds (see map). Historically, bison numbered an estimated 20-30 million. Their constant grazing helped shape the ecology of North America’s Great Plains. Many species of plants and animals depended on them or benefited from them. Prairie dogs preferred the heavily-grazed areas they left, large wolf packs hunted them, and numerous scavengers feasted on bison carcasses.

Mass Slaughter of Bison

Unregulated shooting of bison, which culminated in mass slaughters during the 1870s, reduced the population to 1,091 in 1889. In 1893, efforts to protect the animals began.

Bison Populations Today

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 live in conservation herds. 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). Fewer than 5,000 bison are both free-ranging and disease-free.

The bison genome remains at risk due to cross-breeding with cattle. The few remaining genetically pure wild bison must be conserved separate from cross-bred bison to protect the pure bison genome.

Working Together to Conserve Bison

To overcome these challenges, several scientists, government agencies, tribes, first nations, and non-governmental organizations are working together to conserve North America’s bison. The Bison Specialist Group of the World Conservation Union’s Species Survival Commission is drafting a status report and conservation action plan for North American bison. The document will serve as a benchmark against which to evaluate conservation and recovery into the future and will provide guidelines for reintroductions and management of public and private herds.

Defenders of Wildlife will work with several others to implement the guidelines of the completed action plan. In the meantime, we are working now to protect Yellowstone’s bison herd from slaughter, and to restore or increase bison herds on public lands.

Ultimately, bison will need enough land to support bison numbers in a wild state subject to natural selection, including predation by large carnivores such as the wolf. Dale Lott, professor emeritus at University of California Davis, in his book, American Bison: A Natural History, suggested that we need 5,000 square miles (3.2 million acres) to support an adequate restoration program for bison. Defenders of Wildlife is a participant of the Northern Plains Conservation Network, a network of organizations working toward this goal.

Fact Sheet

Bison Fact Sheet

Historic range map

Yellowstone National Park Bison

Yellowstone National Park’s bison herd is the most important and only large wild free-roaming herd in the nation, and one of only two herds that are genetically pure descendants of the great herds of bison that used to blanket the western landscape. But that doesn’t stop the Montana Department of Livestock, Yellowstone National Park, and other state and federal agencies from slaughtering them when they roam out of the Park, in search of food to survive the winter and enter the state of Montana. 

Pushed by harsh winters and their instinct to survive, bison often roam outside of Yellowstone National Park in winter to reach lower elevations where they can more easily reach needed forage. This movement outside the park is a natural process, similar to the seasonal migrations of elk, deer and other Yellowstone wildlife.

During the 1990s, roughly 3,000 bison were killed by state and federal government agents over alleged concerns about the disease brucellosis even though there has never been a single confirmed case of brucellosis transmission from wild bison to cattle. Also, Greater Yellowstone's elk also test positive for brucellosis. Any attempt to reduce brucellosis in Greater Yellowstone wildlife won't be resolved solely by controlling bison.

In June of 1998, federal and state agencies released a draft 15-year plan for managing Yellowstone's bison. This was the first time in nine years that the public had been asked to comment on how Yellowstone's wild bison should be managed for the long term. The draft plan identified several alternatives, including the government's preferred plan. None of these alternatives achieved the objectives of maintaining the wild, free-roaming nature of Yellowstone's bison while pursuing reasonable, cost-effective risk management.

In response to this faulty plan, Defenders and a coalition of regional and national conservation organizations came up with an alternative plan called The Citizens’ Plan to Save Yellowstone Buffalo. Public support for this alternative was overwhelming: of the 67,000 people who commented, more than 47,000 supported the Citizens’ Plan. Incredibly, the federal and state agencies in charge of the plan ignored public sentiment and adopted a final plan that continues the controversial, intrusive and expensive approach to managing our nation’s most cherished bison herd. It expends millions of taxpayer dollars each year to capture, corral, test, vaccinate, ship, kill and sell bison, while largely restricting bison from using public lands outside the park.

Although a final plan has been adopted, Defenders and our coalition partners will continue to fight to protect Yellowstone’s bison.

Learn more about bison management and policy in and around Yellowstone National Park.