The Siamang (Symphalangus syndactylus), is an arboreal gibbon native to the forests of Malaysia, Thailand, and Sumatra. Its range overlaps with the Lar Gibbon and Agile Gibbon. While the illegal pet trade takes a toll on wild populations, the principal threat to Siamang is habitat loss in both Malaysia and Sumatra. Palm oil production is clearing large swathes of forest, reducing Siamang habitat, along with other species such as the Sumatran Tiger.
The Siamang can be twice the size as most other gibbons. It reaches about 40 inches in height and weighs up to 50 pounds. It is distinctive for two reasons to other gibbons as well. The first is that two fingers on each hand are fused together. The second is the large “gular sac” (found in the male of the species), which is a throat pouch that can be inflated to the size of its head, allowing the Siamang to make loud resonating calls or songs.
The Siamang tends to rest for more than 50% of its waking period (from dawn to dusk), followed by feeding, moving, foraging and social activities. It takes more rest during midday, taking time to groom each other or play. During resting time it usually uses a branch of a large tree lying on their back or on their stomach. Feeding behaviors, foraging, and moving are most often in the morning and after resting time.
In the dry season the length of the Siamang’s daily range is longer than in the rainy season. The Siamang in southern Sumatra undertakes less foraging than the Siamang in other places because it eats more fruit and therefore consumes more nutrition, which results in less time needed for looking for food. Sometimes the Siamang will spend all of the day in one big fruiting tree, just moving out when it wants to rest and then coming back again to fruiting trees.