Mature bulls live alone or in small groups, but during the mating season (July to September) they join herds of females and immature males to fight over females which are ready to mate. Each mature female can calve once every two years.
Males fighting over a female will first bellow at each other and stamp their feet. If neither backs down, they charge each other, butting heads until one of them retreats. The victor mates with a female, and stands guard over her for several days to prevent other males from mating with her. The calf, when born weighs about 30kg, and is able to stand and run within a few hours.Read More: Bison, History and Humans