They will not grow their long, adult hair until 2 to 3 years old. During the first year, mothers closely guard and care for their infants. Young are weaned at about 1, at which time fathers take over their daily care until the juveniles can live without assistance at about age 3. Between 6 to 8 years old, subadult siamangs leave their family units to establish their own families. Powerful upper limbs and limited body weight enable siamangs to swing on branches and vines with great agility.
Siamangs hook, rather than grasp, branches with their hands.
In the wild, siamangs rarely descend to the forest floor. When required, however, they are efficient at bipedal walking on the ground or along branches, holding their arms above their head for balance. Of all the gibbon species, siamangs form the closest social ties within the family unit. Food is generously shared among all family members. Grooming among family members is their most common social behavior, followed by play centered on the infant.