The Story
An American bison stands deep in a Wyoming snowfield with its face pressed into the drift, and it is not grazing so much as excavating. Head low, it drives forward and bulldozes the snow aside.
The forehead does the shoveling, and whatever is edible under the snowpack is the point of the exercise. There is one animal in frame, dark-headed and broad, alone against the white.
Bison are built for this kind of roadwork. The hump over the front shoulders is the giveaway: large shoulder and neck muscles let a bison swing its head side to side to clear snow from a foraging patch. Thick, long, dark hair covers the head and front of the body, so the part of the animal doing the plowing is also the shaggiest. The horns, short and curving out and up, ride above the work. Both sexes carry them, so they settle nothing about whether this is a bull or a cow.
The prize is ordinary. In Yellowstone, more than 90 percent of a bison's diet is grasses, sedges and other grass-like plants, and a bison eats about 1.6 percent of its body mass in dry vegetation every day. A bull can reach 2,000 pounds. Under deep snow, that daily ration has to be uncovered before it can be eaten.
Winter in high country is a margin game. Thick skin and underfur, long guard hairs and layers of fat hold the heat in. Even so, on average 9 of every 100 adult Yellowstone bison die in winter, and 20 to 40 of every 100 first-year animals may die.
Mountain bison once drifted down to lower valleys when snow piled up; herds in the U.S. now move mostly within parks and nearby land. This one has a patch and a plan, and the plan is a forehead-wide trench, one push at a time.
