The siamang is a monogamous primate, with breeding pairs remaining together for life (10). Each pair lives in a family group, with up to three offspring (11). Together this group lives in a small, stable home range of 15 to 35 hectares, most of which is defended as a territory (5) (8) (11). The social bonds within the group are maintained by considerable mutual grooming (3) (8) (12).
Activity starts at dawn, and ends one to two hours before dusk (11), when the siamang retires to one of the tallest trees in the forest to sleep (1). Much of the morning is spent travelling and feeding, with periods of rest increasing in the afternoon (11).
The diet of the siamang comprises primarily of fruit and leaves, although it may also consume insects and flowers (2) (3). Around 20 to 50 percent of the siamang’s diet consists of fruit, with figs from Ficus trees being especially important (11). Around 40 to 65 percent of its diet is young leaves, with the actual proportion varying according to the time of year (11). Leaves from lianas (woody vines), such as the water vine and monkey’s ladder, are especially important, as they provide a greater abundance of leaves than most forest trees (2).
The siamang produces a single offspring at two to three year intervals (11). The infant is born after a gestation period of around 230 days and initially clings to its mother, but shortly after reaching one year of age, the adult male takes over most of its care (8). The young siamang leaves the family group at around six years of age, and may then spend several years searching for a mate, reaching sexual maturity at eight or nine years of age (8).
Due to its high position within the canopy and its quick, agile movement through the forest, predation is not of great concern to the siamang. However, a fully grown siamang was once found in the stomach of a python (13).
In the early hours of the morning, the powerful song of the siamang fills the forest (10). This singing, which can be heard up to around two kilometres away (10), includes duets by the adult male and female, and functions to establish and maintain pair bonds, and to advertise their presence and territory (6). These vocalisations have been known to continue for around fifteen minutes, and are much louder than those of other gibbon species (3).