In the early 1800s more than 65 million bison roamed North America, now their numbers have been reduced to approximately 3900. Bison in the U.S. are mostly confined within the perimeter of Yellowstone National Park but heavy snows in recent years have led them to roam to lower elevations where it is easier to forage for vegetation. Montana farmers fear roaming bison could spread brucellosis, a disease which causes abortion or premature calving, to their livestock though there have been no documented cases of bison to cattle transmission. In response to this concern the State of Montana has developed a bison management plan. Bison entering Montana along Yellowstone's north boundary would be shot or shipped to slaughter and all bison entering Montana through the park's west boundary would be tested for brucellosis. Any bison testing positive for the disease would be shot or shipped to slaughter. Currently 400 animals are being held in government-operated pens near Gardiner, Montana.
The Defenders of Wildlife organization argues that such a lethal approach is unnecessary and has started an online petition to save the Yellowstone bison.