Elephants are large, herbivorous mammals classified in the order Proboscidea. Male elephants are called bulls and live solitary lives or in small groups after leaving their family unit between 12-15 years old. Female elephants live in family units called natal units led by the oldest female, the matriarch. Elephants communicate through sounds and touch each others with their trunks. Both male and female elephants enter periods of increased aggression and sexual activity called musth. Elephants spend over half their sleeping time standing and are most active at dawn and dusk. Babies weigh 200-250 pounds at birth and nurse through their mouths until their trunks are strong enough.