Large herds of European bisons of several dozen individuals are quite rare. This association of smaller groups may occur in winter. During the rest of the year, each herd has no more than twenty animals, mostly young and females. One of the females becomes the leader. Calves are born from late spring to mid-summer and feed on their mother’s milk throughout the year. Four years after birth, the European bison reaches the age of puberty and, if it is a male, leaves the herd to start an independent life, or to join a group of other young males until it becomes strong enough to live as a single animal (singleton). Some bisons can live up to twenty-eight years.
August and September are the mating season for European bisons. In natural conditions, this is the most suitable time for the rut, as it can not take place in a heatwave, in a cold period, or when the amount of feed is insufficient. Now the boundaries of the rut periods are somewhat blurred due to the long-term breeding of bisons in captivity and the creation of year-round favorable conditions for them. For mating, the male briefly joins the herd. In the case of competition with other males, duels can occur between them, sometimes quite serious and dangerous for the participants. After successful mating, the female bears one calf for nine months.