In summer, adult male pronghorns fight with other males for a territory. In this territory the male keeps a group of females with which he mates in September. Adult males go to the extremes in fighting each other to win over the female by fatally injuring the other pronghorn and determining which male is stronger. Young males that do not yet fight for a territory form small groups, and old weak males live alone. Females live in groups of about 20 animals. When the female is close to giving birth, it leaves the group for a time to give birth to its offspring. 