Elephants are social animals, usually living in herds. The females, called cows, and their young, called calves, live in herds of 15 to 40 individuals led by a mature cow. The males, called bulls, are either solitary or live in herds (usually small in size) with other bulls. Large temporary herds containing hundreds of individuals of both sexes sometimes are formed during unusual occurrences, such as droughts.
Most elephants have no fixed mating season. Some populations, however, have a mating season from November to April, during which mature bulls go into musth, a period of aggressiveness triggered by the secretion of hormones from a gland in the head. Cows in estrus (a recurrent state of sexual excitability) emit low-frequency calls that can attract bulls more than two miles (3.2 km) away. About 22 months after mating, the cow normally bears a single calf. The calf weighs about 220 pounds (100 kg) at birth and is 3 feet (90 cm) tall at the shoulder. It is covered with brown, fuzzy hair, most of which is shed as the calf matures. The calf usually nurses no longer than 18 months, though some nurse for more than 6 years. Sexual maturity can occur anytime between ages 10 and 22. Elephants can live to 80 years.