No facial fringe or tail. Upper canopy of forested regions of Sumatra and the Malay Peninsula from 500 to 2500 feet. Fruits, leaves and other plant products. Probably also small animals, insects, birds and birds' eggs. The long adult hair does not appear until 2-3 years of age.
Infant is weaned at one year.
When there are older youngsters in the family, the father gives the older ones protection and affection while the mother tends the infant. Siamangs mature at 8 years of age and at that time leave their parents. They sleep upright, sitting on their ischial callosities, arms folded and head between knees, unlike great apes who build sleeping nests or platforms. Well-developed forearms and limited body weight and hooklike hands facilitate brachiation. May hold or carry objects with feet.