Mothers give birth to a single calf in June or July, after a gestation period of about six months. The calves are precocial, being able to stand within 15 minutes of birth. They are fully grown within 15 months, and reach sexual maturity during their second or third year. Although females may remain with their mothers until they themselves give birth, males leave within 12 months, by which time their horns are beginning to grow. Males determine status by their relative horn length, with the maximum length being achieved at around three and a half years of age.