Bison Pet

The only continuously wild bison herd in the United States resides within Yellowstone National Park. Numbering between 3,000 and 3,500, this herd is descended from a remnant population of 23 individual mountain bison that survived the mass slaughter of the 1800s by hiding out in the Pelican Valley of Yellowstone Park. In 1902, a captive herd of 21 plains bison was introduced to the Lamar Valley and managed as livestock until the 1960s, when a policy of natural regulation was adopted by the park.
The end of the ranching era and the onset of the natural regulation era set into motion a chain of events that have led to the bison of Yellowstone Park migrating to lower elevations outside the park in search of winter forage. The presence of wild bison in Montana is perceived as a threat to many cattle ranchers, who fear that the small percentage of bison that carry brucellosis will infect livestock and cause cows to abort their first calves. However, there has never been a documented case of brucellosis being transmitted to cattle from wild bison. The management controversy that began in the early 1980s continues to this day, with advocacy groups arguing that the Yellowstone herd should be protected as a distinct population segment under the Endangered Species Act.