Bison are born in an isolated location that has a lot of cover. Male calves are born a little more frequently than females. The young calves are red in color. They begin turning brown in two and a half months and are entirely brown in four months. Calves are nursed for seven to eight months and are fully weaned by the end of the first year.
Females are seasonally polyestrous with a cycle of approximately three weeks.
Cow groups are composed of females, males under three years of age, and a few older males. More males enter these groups as the rut approaches. Males live either individually or in groups that may be as large as 30 head. Dominance between the bulls is linear. Bulls that have a higher rank in the society breed more often than those of a lower rank.