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The Scoop on Siamangs

Close-up of female siamang

Knowledge is crucial to conservation (and, I mean, life in general, but that's outside the scope of this blog). But how many primates do you know of? Do you know how many species there are in the world? (505, according to the IUCN database!) Do you know the differences between a monkey and an ape? Maybe you do, maybe you don't. Either way, a goal of this blog is to spread awareness of primatology and issues regarding primates; one way we've decided to go about this is to highlight a different species of primate and give them their own, full-length post!

So, without further ado... meet the siamang!

Just look at that face. So grumpy. So precious.

Siamangs, or Symphalangus syndactylus, are the largest species of gibbon. Gibbons, often called "the lesser apes", are the only nonhuman bipedal primates (they walk on two legs just like us, though not in the same way, and not as often as us). Greater apes (i.e. gorillas, orangutans, chimpanzees, bonobos, and us!) split from lesser apes (family Hylobatidae) about 20 million years ago. Siamangs are also the only gibbons with a large gray or pink inflatable throat sac!

Found in Malaysia and Sumatra, siamangs are an endangered species due to forest fragmentation and destruction. They primarily live in the tree canopy and prefer to sleep in the tallest trees. Currently, 40% of their habitat in Sumatra has already been destroyed and thousands of kilometers of forest in Malaysia are logged each year. On top of that, siamangs are the most traded gibbon species for the illegal pet trade. (Boo.)

Northern Sumatra is the only place in the world where three nonhuman apes live sympatrically (read: alongside); this includes the siamang, the lar gibbon, and the Sumatran orangutan!

Siamangs eat primarily fruit and leaves. Those in mainland Asia are typically folivorous, while those in Sumatra are typically frugivorous and eat figs. You can check out more about primate diets in our last post!

Siamangs are diurnal, meaning that they are active during the day and sleep at night. They don't have tails and have shaggy black fur with gray fur around the mouth, while infants are completely black. They grow to be about two and a half feet tall from head to rump, and weigh between 17 and 28 pounds, with males being slightly larger than females. Gibbons have opposable thumbs, like us, but siamangs have opposable thumbs and toes, allowing them to grasp with their feet!

Fun fact! Their scientific name, Symphalangus, comes from the Greek words "sym" and "phalanx", loosely meaning "together fingers". This is in reference to their webbed second and third toes!

Gibbons as a whole are very melodic, often singing and harmonizing with each other. Their voices can be heard up to 2 kilometers (about 1.25 miles) away! Check out this video of a siamang duet. Heads up, it can get pretty loud.

Siamangs often form monogamous social groups consisting of parents and their offspring. They like to maintain their relationships with each other through a ton of mutual grooming. Interestingly, they are also known to form polyandrous groups, with two adult males and one adult female.

Even though gibbons are bipedal like us, they have the longest arms of any primate. But what exactly does that mean? First, their arms are much longer than their legs.

They are arboreal and move through the trees by brachiating, or by swinging from tree to tree using only their arms (watch a video of a siamang brachiating here). When brachiating, gibbons use only four fingers, like a hook, and don't engage the thumb. Imagine hanging from a tree with only four fingers. YIKES. I don't recommend challenging a gibbon to the monkey bars--they'll definitely win. Because they brachiate as their main mode of locomotion, their bodies have adapted in ways unique to gibbons. The radius in each forelimb is thicker sagitally (left to right) than it is transversely (top to bottom), and siamang forelimb muscles are especially adapted for brachiation. Their elbow flexors (muscles that allow for bending) appear to be adapted for brachiating while changing speed and direction.

So, to summarize:

1) Siamangs are a species of gibbon

2) They are endangered (but cute)

3) They live with other primates, sometimes with other apes

4) They eat fruit and leaves, and like figs (probably don't like Fig Newtons, though)

5) They sing together!

6) They brachiate and have the arms to show for it

And last, but not least, here is a final video of siamangs, complete with a baby clinging to its mother!

So, what do you think about the siamang? Do you have a favorite primate? Let us know!


Photo credits:

Close-up of female siamang

© Wegner / ARCO /

Nature Picture Library 5a Great George Street Bristol BS1 5RR United Kingdom Tel: +44 (0) 117 911 4675 Fax: +44 (0) 117 911 4699

Siamang hanging

© Anup Shah /

Nature Picture Library 5a Great George Street Bristol BS1 5RR United Kingdom Tel: +44 (0) 117 911 4675 Fax: +44 (0) 117 911 4699

Siamang walking

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