Young calves are a reddish brown color through their first summer. A tail hanging loosely behind indicates that the animal is relaxed. If the tail is partially raised, the bison is alert. If the tail is horizontal, the bison is excited. After weaning from their mothers milk, young bison feed on a variety of green plants for the rest of their lives.
Bison feed mostly on grass.
They also eat a few other small plants, as well as twigs of willows and low shrubs. To forage in winter, a bison sweeps aside snow with its muzzle and digs down with its hooves as deep as four feet to get at succulent grass. Both the bull and cow have a pair of fairly short horns that they retain from year to year. The bull's horns curve upward and are used as weapons of attack. A cow's horns curve but are more slender.