Both males and females have short black horns curving upward then inward with narrow tips. Horn spread may reach 3 feet. Breeding may occur at any time of year, with peak season from June to early fall. Most calves are born from March to June. Gestation period is 270 to 285 days.
Twin calves are very rare.
A newborn will stand to nurse within 30 minutes, walk within hours and in 1 - 2 days join the herd with its mother. It is fully mature at 3 years. Bison cows up to 30 years of age have been known to produce a calf. Single sex herd size is usually 4 - 20 animals. During the summer and early fall breeding season, herds of mixed sexes can be seen.