The bulls and the cows finally join together as a herd during the summer. The mating season, known as the rut,begins and lasts until early fall. The calves are really growing.
Dark horns break the skin and their coloring darkens.
The baby hair falls out and molting occurs as the darker hair pushes from beneath. The hump is starting to develop. The adults rub against any available object and wallow on the ground to rid themselves of their molting pelage, and to scratch themselves when insects make them itch. When telegraph lines first crossed the prairies, many were knocked down by bison rubbing and scratching. During the winter the bison are split into two separate groups.