This spring about 1,100 fewer bison roam Yellowstone National Park than did so last fall. Over the winter, state livestock managers and hunters drastically culled the herd in an attempt to prevent the spread of brucellosis, a contagious disease that can cause cattle to abort. A record number of bison were shot or captured for slaughter as they left the park in search of food, provoking an outcry among environmental groups.
Montana livestock owners view free-ranging bison as a threat to their livelihoods. Cattle that contract brucellosis must be destroyed, and if Montana loses its disease-free status, every cow shipped from the state would have to be tested—a financial burden for ranchers. Brucellosis has been eradicated nationwide except for pockets of infection among bison and elk in the Yellowstone area.
The slaughter has prompted ranchers and state and federal officials to renew efforts to devise a nonlethal solution to the problem of wandering bison. A $2.8 million, as-yet-unfunded management plan would remove cattle from an adjacent ranch, allowing bison to migrate in the winter to graze on public land. Federal agriculture officials favor vaccinating the Yellowstone bison against brucellosis, but such a vaccine hasn't been approved.