American bison have lived in Hayden Valley for thousands of years, sustained by its broad grasses and sedges. Nearly driven to extinction in the 1800s by homesteaders, hunters, and the United States government, they now thrive under protection in Yellowstone and have become an icon of American conservation. Bison are born in Hayden Valley and live and die there, but survival through its bitter winters depends on strength, heavy fur, and fat reserves. Each year instinct leads them either to remain in the valley or to migrate to lower elevations in search of food, returning to Hayden in spring to begin the cycle again. Although wolves prey on these bison, weather is their greatest enemy, and during harsh winters they follow traditional migration routes, with most moving toward Yellowstone’s west boundary and about a quarter of the adult herd migrating north to the Northern Range.