In the zoo they are fed fruit, vegetables and monkey chow. Siamangs bear one offspring after a seven- month gestation period. At birth, the young are naked, and for the first few months, the baby clings to the mother's abdomen. She, in turn, keeps her legs partially raised to provide warmth and support. By the age of two, the baby is independent but still very much a part of the family.
Sexual maturity is reached at about seven years of age.
In the wild they live from 25 to 30 years. Like other gibbons, the Siamang is declining in numbers as man enters its forested territory, often killing the mothers in capturing the young for a lucrative pet market.