The Story
Snow has packed itself into the face of an American bison, over the brow, around the horn, in a white clump just above one dark eye. It is a Yellowstone blizzard, and the animal keeps working.
The head does the heavy lifting. A bison carries that skull on a hump of shoulder and neck muscle, and in deep snow it swings the head side to side to clear a patch down to the grass. This is a grazer through and through: Yellowstone bison get more than 90 percent of their diet from grasses, sedges and other grass-like plants, and typically forage 9 to 11 hours a day. In a blizzard, every mouthful starts as a shovel job.
Look at the coat. Snow settles on the back and sits there in cracked plates. Underneath are thick skin and underfur, long guard hairs and layers of fat, insulation for a body that weighs up to 2,000 pounds in a bull and 1,000 in a cow.
That a herd is here at all comes down to a narrow escape. Bison once ranged from Alaska to northern Mexico, an estimated 30 to 100 million of them before 1800. By the 1890s fewer than 1,000 were left, and poachers cut Yellowstone's wild herd to about two dozen by 1902. Those last animals held out in a remote valley deep in the park. That same year the U.S. Army brought in 21 bison from two private herds, which later mixed with the wild ones. Bison have lived in Yellowstone continuously since prehistoric times.
Then the snow gets too deep to dig. A cow at the front gives the signal, and the bison fall into line behind her. Traveling herds take that shape, a line with an adult cow at its head. As the light fades, the column follows her trail out of the valley toward the warmer heart of the park. It is the first step of a migration, and Yellowstone bison migrate up to 70 miles between summer and winter ranges.
