At daybreak and dusk the forest resounds with siamang calls. Calling in unison develops and maintains the pair bond and excludes neighboring groups from the family's territory. Siamangs mate for life. Births of a single 1.5 pounds baby occur every 2 – 3 years after a 230–235 day gestation.

How do siamang reproduce?

​Reproduction and Family

Nearly all siamangs are monogamous, with a mating pair producing a newborn every 2 or 3 years. The mother is pregnant for a period of 7 to 8 months. Once born, the baby siamang will cling to his mother for around 8 months.

Why do gibbons inflate?

Second, a large gular sac (throat pouch), found in both males and females of the species, can be inflated to the size of the siamang's head, allowing it to make loud, resonating calls or songs. ... The siamang can live to around 40 years in captivity.