Yellowstone NP

19. Bison Herd

Bison often move across the landscape that they graze. Most bison remain in the park during the winter, living off stored fat as snow and ice make forage difficult to reach. But by early spring some bison usually leave the park following established routes in the Yellowstone and Madison river valleys leading them into Montana. Here with the elevations lower and the snow and ice pack less, they can forage easier. While these areas had been their historic range, it now contains public and private land the cattle use for their grazing in summer. While most bison return to the park by late spring, they must not be on cattle grazing land when the cattle arrive to prevent possible brucellosis infection to the cattle.