Siamang: The Large Gibbon of Sumatra’s Forests
Siamang: the largest gibbon of the Sumatran forest
The siamang (Symphalangus syndactylus) is the largest of the gibbons, the small apes of Southeast Asia that travel through the trees by swinging from their arms. It is an arboreal primate with black fur, found in the tropical rainforests of Sumatra and the Malay Peninsula. Its loud calls carry a long way through the forest, so visitors often hear a siamang well before they see one. It is one of the most distinctive members of the primates of Indonesia, and it is covered in the Indonesian wildlife guide.
What sets the siamang apart from other gibbons
The siamang is the only species in its genus, Symphalangus, so no other living animal shares that name. It has two features that distinguish it from other gibbons. The second and third toes on each foot are partly joined by a membrane, which gives the species its specific name, syndactylus. The siamang also has a large gular sac, a throat pouch found in both males and females, which can be inflated to roughly the size of its head. Inflating the pouch lets the animal make the resonating calls for which it is known. Some siamangs are up to twice the size of other gibbons, such as the agile gibbon and the Bornean gibbon.
Diet, pairs and the morning duet
Siamangs eat mainly plant material, especially leaves and fruit, and they also take insects and bird eggs. Because they feed on fruit, they help disperse seeds across the forest as they move through their home range. Siamangs form monogamous pairs. Mated partners sing duets, loud and patterned calls that advertise their presence and mark their territory. These duets are a central part of the siamang’s social life, and they strengthen the bond between the two partners.
Range and conservation status
The siamang lives in the Barisan Mountains of Sumatra and across the Malay Peninsula, where it is found in the tropical rainforests of both regions. The International Union for Conservation of Nature lists the species as Endangered. The main threat is the destruction of forest habitat for logging and agriculture, which has reduced the forest where siamangs can live.