Elephants form matriarchal (female-led) societies. The oldest, most dominant female in the group is known as the matriarch, and she is the backbone and leader of of the family unit, which might contain her adult daughters, their calves and a number of juveniles of both sexes. As matriarch she is the most experienced female and provides stability as well as determining the group's movements. Males usually leave the family between 12 and 15 years old. Younger bulls may join with other males to form small bachelor groups with hierarchy based on age and strength. Older adult males tend to become solitary and nomadic, occasionally joining family groups to find reproductively receptive females.