In the 1970's and 1980's, there were a series of cool, wet summers followed by mild winters. These conditions allowed for an abundance of grasses for the bison to feed on and a reduction in the winter mortality rate. In addition, snowmobiling in the park has helped more bison survive winters since the groomed roads cut down on the amount of energy that a bison uses to travel when compared to traveling through deep snow. By the winter of 1996 to 1997, there were approximately 3,500 bison in Yellowstone National Park. An adult bull bison may be six feet tall at the shoulder and weigh 2,000 pounds.
Females look like the males except that they are smaller and have more slender horns.
May. During the spring and early summer, new-born calves can often be viewed in the Firehole area and Lamar Valley. Although viewing the young calves can be an exciting experience, it is very important that you do not get too close to the animals for observation or photographs. Bison may appear big and slow, but they can run up to 30 miles per hour. Yellowstone visitors are gored every year, because they venture too near in attempts to photograph the animals. Today, the Yellowstone bison still faces conflict and struggle.