Siamang Fact File
Siamangs are slightly larger than other gibbons and have long, shaggy black hair all over their body although they do have some paler hair around the mouth and chin areas. The face does not have any fur on it around the eyes and mouth.
They have a throat sac which is grey or pink in colour which they inflate during vocalisations. This throat sac can be quite large, up to about the size of a grapefruit.
They have much longer arms than legs, and these can reach 2.5 times the length of their body. They have hands very similar to ours and have four long fingers and an opposable thumb, their feet have five toes and the big toe is opposable. Siamangs also have webbing between their second and third toes, and they can carry and grasp things with both their hands and feet.
Just like other gibbons they have tough, horny pads on their rear. These are known as ischial callosities and help the siamang have a more comfortable night sleeping in the tree branches safe from predators.
As an ape the siamang does not have a tail.
The average length of the siamang is 75 to 90 cms (29.5 to 35.5 in) from their head to rump and the average weight is 8 to 13 kgs (17 to 28 pounds).
Siamangs are omnivores. They forage for food in the forests during the day with most of their diet being made up of leaves and fruit. They also eat flowers, tree bark, plant shoots and seeds, as well as bird eggs, spiders, small birds and insects.
They play a role in seed dispersal. When a siamang eats fruits the seeds are deposited around the forest in their feces and this helps lead to a greater diversity of trees in their habitat.
To obtain water they are often seen to drink by dipping their hands into the water or rubbing their hands over wet leaves and then licking the water from their fur.
8-13 kgs (17-28lbs)
75-90cm (29.5-35.5 in)
Captive Over 30
Asia is the native home of the siamang. Here they can be found in Indonesia, Malaysia and Thailand. In Indonesia they are found on the island of Sumatra.
Reports exist of this species from Myanmar but scientists believe these are certainly an error.
They make their home in semi-deciduous and tropical evergreen forests. Siamangs appear to have a level of tolerance to habitat disturbance and can persist in some secondary forest areas.
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Siamang pairs will partner for life, a rare trait among primates. Mating will typically occur from May to July leading to the birth of an infant from December to February.
Their gestation is 7-8 months long. At the conclusion of this a single infant is born at a time which lacks hair across its body except for a small tuft on top of their head. At birth they weigh 170g (6oz).
They start their life by clinging to the fur of the mother who will carry the infant through the forest.
Around 1 year old the male will take over daily care responsibilities for the infant, another unusual behavior for a primate.
Infants are weaned by 2 years old. The infant remains with its parents for a further five to seven years. This extended care period means they are with the parents while they raise multiple siblings and allows them to learn the necessary skills to raise their own young.
At the conclusion of this period they move off to form their own pair. It can take multiple years for them to find a partner.
As many as ten infants may be produced by a female in her life.
One of the most recognizable behaviors of the siamang is their call. This loud, throaty vocalization is amplified by the throat sac. Males and females perform their call as a duet and this helps to strengthen family bonds. These calls can travel up to 2km (1mile).
Another way to reinforce their bond is to groom with adults typically grooming one another in the morning.
Each family which is made up of the pair and their offspring maintains a territory which is defended against intruders.
Most of their movement occurs in the trees where they will swing from tree to tree assisted by their long arms. On the ground though they are considered to be the most skilled gibbons at walking upright.
At night the siamang will sleep on a tree branch sitting upright with their arms folded.
Predators and Threats
Their large size and ability to move quickly through the trees mean they have no recorded predators.
Humans have had a large role in the decline of the siamang. They are threatened by habitat loss which is undertaken for logging, conversion of the land to plantations including for palm oil and poaching for the illegal wildlife trade.
The siamang is the largest member of the gibbon family. On average they are twice the size of other gibbons.
Siamangs are one of the few primates that form permanent pairings with their mates.
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Starr, E., 2020. Siamang. [online] New England Primate Conservancy. Available at: <https://www.neprimateconservancy.org/siamang.html> [Accessed 18 August 2020].
Nijman, V., Geissmann, T., Traeholt, C., Roos, C. & Nowak, M.G. 2020. Symphalangus syndactylus. The IUCN Red List of Threatened Species 2020: e.T39779A17967873. https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T39779A17967873.en. Downloaded on 18 August 2020.