They do not do very well in captivity. They are fully grown and able to reproduce at 5-7 years old. Newborn siamangs are hairless except for a small cap of fur on the top of the head. Babies weigh only about 6 ounces at birth. Female siamangs carefully nurture their young.
Babies can grasp their mother's fur to cling to the mother's belly soon after birth.
They are weaned at about 1 year old. Young siamangs stay with their mother for about 5-7 years. All gibbon populations are decreasing, including the siamang. They are threatened with extinction. They are losing their natural habitat as human agriculture encroaches upon it.