Males tend a female by staying between her and the rest of the herd. Tending can last for a few minutes or for several days. If a female isn't interested in a male, she will walk away. Males will threaten and sometimes attack other males that try to get too close to a female he is tending. Fights between males can involve headbutting, shoving, or locking horns.
Females give birth to one calf after about nine months.
They will go to an isolated area to give birth. Newborn bison are reddish brown and can stand shortly after birth. The mother and her calf will stay isolated from the herd for a couple of days. At about two months, the calves will begin to develop shoulder humps and horns. The calves are usually weaned by the time they are seven months old.