Yellowstone National Park
The highest number of bison in the park was 4,900, in 2005. However, there were only 3,000 in 2008. That was after a very cold winter. Hundreds were also killed so that they did not spread brucellosis. Brucellosis is a very infectious bacterial disease. Cattle ranchers worry that brucellosis will spread to their cattle. Every year, park workers and members of Native American tribes kill some bison. This stops the herd from getting too big and spreading the disease. The Animal and Plant Health Inspection Service (APHIS) said that vaccinations and other work could remove all brucellosis from the bison and elk in Yellowstone.