Bison

Yellowstone is the only place in the United States where bison (Bison bison) have lived continuously since prehistoric times. They were also part of the natural and cultural history of the Jackson Hole, Wyoming, area for thousands of years before being extirpated in the 19th century by a combination of commercial, subsistence, and sport hunting, and competition with domestic livestock. Present-day Jackson bison are descendants of 32 bison relocated from Yellowstone and Theodore Roosevelt national parks in the 1940s and 1960s, respectively, and some subsequent migrants from Yellowstone. The largest bison population in the country on public land resides in Yellowstone, and the Jackson herd is now the second largest unfenced bison herd in the U.S. Both populations are among the few that do not contain cattle genes as a result of interbreeding. However, some Yellowstone bison are infected with brucellosis, a livestock disease that has been transmitted to wild bison and elk through contact with infected fetal tissue or afterbirth. The Jackson herd’s discovery in 1980 of the winter elk feeding program at the National Elk Refuge altered natural population dynamics and distribution, and infection with brucellosis reduced tolerance for Jackson bison outside the park and refuge. Access to winter range outside the park has become a key issue for the National Park Service in collaborating with other federal and state agencies because of limited tolerance for bison due to brucellosis and the risk of property damage and human injury.