Before the mating season, male milu deer go through rounds of fierce combat to select their alpha, who then becomes the lord of a harem of female milu deer for the season. Every May, the strongest male is selected by rounds of gladiatorial combat. Male milu deer choose a rival whose physical strength is a match with their own, and they battle. The winner chooses a new opponent, and the battles continue until the last round produces an overall winner. Soon after, all the defeated males are expelled from the herd of females, and must form a new group. One alpha male deer usually has a harem of around 50 females.