Yellowstone's Interagency Bison Management Plan has set a goal of maintaining about 4900 animals in the Park. Bison face very low predation from wolves and bears so the population typically grows 10-17% each year. To keep the population down, animals are hunted or sent to slaughter each winter. In 2021 the goal was to remove between 400-600 animals.
There are 40 hunting tags given to hunters who apply through Montana Fish, Wildlife, and Parks. In 2021, 5260 applied for those tags in a lottery. This year only three tag holders were successful at filling their tags before the February 15th season closure.
Many Native American tribes also have treaty rights to kill bison. Each tribe sets its own rules and provides a game warden when their hunters are present. Some tribes allow two bison per hunter while some allow three. Many only allow bulls or calves to be killed. Most tribes have unlimited seasons. Once the bison begin leaving the Park word spreads quickly and tribal members from around the Northwest come to Gardiner in hopes of getting a bison.