By late spring, the only remaining long hairs are on the head, forelegs, and hump. To escape the torment of attacking insects, buffalo wallow in dust or sand. With the arrival of the breeding season in mid- to late summer, the herds become restless. The bulls, aloof most of the year, now drift among the cows and calves. Noticeably quiet at other times, the bulls bellow hoarsely and become quarrelsome.
Many fights occur over females, and the combatants, with lowered heads, paw the earth defiantly.
Cows give birth usually every year to one tawny to buff-colored calf. Most of the calves are born between the middle of April and end of May, but some arrive as late as October. At birth, the calves have only a faint suggestion of the hump they will develop later. Buffalo may live to be about 20 years of age. By 1800, the small buffalo herds east of the Mississippi River were gone.