© Jim Peaco/NPS


Threats to Bison

Millions of bison once thundered across the Great Plains. For centuries, Native Americans depended on bison as a source of food, clothing and shelter in order to survive on the open plains. But in the mid-1800s, ever-increasing hunting pressure began to take its toll. Unregulated shooting led to mass slaughters of bison in the 1870s, and by 1889, scarcely 1,000 bison remained. Today, wild bison are making a small comeback in a few scattered places, but they need more room to roam.


The greatest threat to bison is the refusal of some humans to accept them. Even though bison are no longer threatened with extinction as a species, they are still not allowed to be a wild animal and perform their important keystone role in their grassland environment, except in a very few small areas. This is why, for all intents and purposes, bison are “ecologically extinct.”

Almost all of their historic stomping grounds are off limits, due primarily to opposition from livestock interests.

Yellowstone National Park – the one place where wild bison were not completely wiped out or reduced to captivity – is home to the largest wild bison herd in the U.S. But even here, bison are not allowed to roam much beyond the park boundary, and are generally kept to fewer than about 3,500 in number. When the herd grows above this level, the “surplus” bison are often shipped to slaughter. The main excuse given for not allowing bison access to lands outside the park is that many Yellowstone bison have brucellosis, a disease first introduced by cattle that causes cows to abort their first calves. Though there have been no known cases of brucellosis transfer from bison to cattle in the wild, the remote chance of occurrence remains the reason for the ongoing intolerance for bison.

Habitat Loss

Wild bison make their home on the grasslands that once covered so much of the central and western U.S. Today, much of these vital habitats have been plowed and built over by humans. Nearly half of all temperate grasslands have been converted to agriculture and urban development. Despite the pace of this destruction and the variety of wildlife that depend on grassland ecosystems, less than 8 percent of all grasslands on Earth are protected.  

However, millions of acres of habitat remain for wild bison restoration. If bison are ever to reclaim their place on the Great Plains, serious efforts need to be made to secure safe habitat for them, and to combat the intolerance toward this animal that was once a national icon.

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