Order : PRIMATES
Family : Hylobatidae
Species : Symphalangus syndactylus

Head-body length : 75-90 cm
Tail length : no tail
Weight : Females up to 11 kg, males up to 15 kg

Play call ►

The Siamang is the largest of all gibbon species, and is confined to tall, montane or hill forest. The species is endangered due to the destruction of its  forest habitat by overlogging or conversion to oil palm plantations, as well as the illegal wildlife trade.

Siamang lead a fully arboreal lifestyle and are more often heard than seen. Males, females and juveniles all possess a large throat pouch which inflates to produce a powerful call which can be heard at a great distance : the call, which is usually made in the morning, comprises loud whoops, barks and yells.

The fur of adults and juveniles is long and jet black : there is a total absence of the white facial markings seen in other gibbons. Their thick fur allows them to live at high elevations, reportedly as high as 3800 metres. Physically Siamang appear stocky, with long, thick powerful arms.

They feed predominantly on vegetation including young leaves, shoots of climbers, flowers, fruits and figs: this is supplemented by occasional high protein foods such as insects.

Unusually amongst primates, male Siamang play a significant role in caring for their young : fully weaned juveniles are carried by adult males during the day, only returning to their mothers at night.

Siamang occur in montane or hilly areas of extreme southern Thailand, Peninsular Malaysia and the Barisan Mountains of Sumatra. The Sumatra population is considered by some researchers to be a separate subspecies.

Fig 1 : Adult and infant moving through the forest canopy.

Fig 2 : Family group in the upper branches of a Giant Fishtail Palm Caryota maxima, comprising an adult male  one female and juvenile (with an infant hidden from view).

Fig 3 : A free-living, but orphaned, immature Siamang descends from the forest canopy each morning to feed on fruits.

Fig 4 : Brachiating and walking along a sturdy branch. Note the muscular arms.

Fig 5 : Foraging in the canopy for young leaves and shoots. 

Fig 6 : Adult calling loudly, with inflated throat pouch. Photo thanks to Vilma D'Rozario.

All images from the Titiwangsa mountain range near Fraser's Hill, Peninsular Malaysia.


References :

Francis, C.M. 2019. A Field Guide to the Mammals of South-east Asia. Second Edition. New Holland. 416 pp.

Lekagul, B., McNeely, J., 1977. Mammals of Thailand. Association for the Conservation of Wildlife, Thailand. 758 pp.