Five live here

Siamang Gibbon

Symphalangus syndactylus

The largest of the gibbons, the siamang fills the rainforest with booming songs from an inflatable throat sac. Meet Jack, Jocko, Katya, Kazoo and SongKhla, the siamangs of Plumpton Park Zoo in Rising Sun, Maryland.

Plan Your Visit Meet Our Siamangs

Close portrait of a siamang holding overhead ropes at Plumpton Park Zoo

Size29–35 in

Weight18–33 lb

Lifespan in the wild25–40 years

Conservation statusEndangered

Our siamangs

Meet Jack, Jocko, Katya, Kazoo and SongKhla

Five siamangs, and you will hear them before you see them.

JackJockoKatyaKazooSongKhla

Five siamangs live at Plumpton Park Zoo: Jack, Jocko, Katya, Kazoo and SongKhla.

The Siamang gibbons are rare, small, slender, long-armed, tree-dwelling apes. Siamangs live in the upper canopy of tropical rainforests in Malaysia and Sumatra (in southeast Asia). They have long, dense, shaggy, black hair on most of their body. Like all apes, they have no tail. Siamangs can also leap acrobatically from tree branch to tree branch across large gaps in the tree canopy. They have been known to leap over 30 feet in a single jump! Siamang gibbons sleep sitting upright in the fork of a tree, usually alone but sometimes huddled together. They are monogamous and have an enlarged throat sac to amplify their sound.

Two siamangs sitting close together indoors at Plumpton Park Zoo, one resting a hand on the other's head — Two of our siamangs, side by side.

Two siamangs hanging by their long arms outdoors at Plumpton Park Zoo — Two of our siamangs showing their long reach. Photo: Nicholas Lacovara.

Field guide

The biggest gibbon, built for swinging

A siamang sitting in the sun on the grass at Plumpton Park Zoo, one long arm reaching up to a window ledge — Soaking up the sun at Plumpton Park Zoo. Note the long arms.

Siamangs are the largest of the gibbon species, and their arms are longer relative to their body than any other primate’s. A siamang’s arms can be two and a half times the length of its body, and its arm span can reach almost 5 feet. Swinging hand over hand, called brachiation, a siamang can cover up to 10 feet in a single swing.

A family defends a territory of about 60 acres of forest in the Malay Peninsula and Sumatra, living high in the canopy, often more than 80 feet above the ground. Studies have measured siamang home ranges anywhere from 28 to 95 acres. In the wild they live in the Barisan Mountains of Sumatra and in the mountains of the Malay Peninsula south of the Perak River.

Look closely at a siamang’s feet: the second and third toes are joined by a thin web of skin. Males and females look alike, both covered in long, shaggy black hair. The bare throat sac, gray or pink, is the siamang’s signature. Smithsonian scientists describe it swelling to the size of a grapefruit; others compare it to a human head.

Sources: Smithsonian’s National Zoo; Animal Diversity Web (University of Michigan); Primate Info Net (Wisconsin National Primate Research Center); New England Primate Conservancy; Kyiv Zoo (non-US zoo).

At a glance

Siamang fast facts

Scientific name Symphalangus syndactylus

Animal group Mammal — ape (gibbon)

Native region Malay Peninsula and Sumatra

Habitat Upper canopy of tropical rainforest

Diet Fruit, leaves, flowers, seeds, bark, insects

Size 29 to 35 inches

Weight 18 to 33 lb

Arm span Up to about 4.9 feet

Feet Second and third toes joined by webbing

Home range About 28 to 95 acres

Weight at birth About 1.2 lb

Lifespan 25 to 40 years in the wild

Conservation status Endangered (IUCN)

Sources: Smithsonian’s National Zoo; Animal Diversity Web (University of Michigan); Handbook of the Mammals of the World, vol. 3 (2013); Malaysia Biodiversity Information System; Primate Info Net (Wisconsin National Primate Research Center); New England Primate Conservancy; Kyiv Zoo (non-US zoo).

2 miles

how far a siamang’s call can carry through the forest.

The morning song

A family that sings together

That throat sac can inflate to the size of a grapefruit, letting siamangs produce loud whooping calls that carry for up to two miles through dense rainforest — used both to mark territory and to strengthen the bond between mated pairs, who often “sing” together each morning. A morning song can last up to 30 minutes.

The song mixes two very different sounds: a deep boom made with the mouth closed and a loud “wow” made with it open. The low boom carries farther through the forest than the high-pitched wow.

Sources: New England Primate Conservancy; Primate Info Net (Wisconsin National Primate Research Center); Smithsonian’s National Zoo.

Behavior

Life high in the trees

Siamangs travel by swinging through the trees and can launch themselves across gaps of 25 to 32 feet. A family usually travels no more than about a mile a day, keeping about 30 feet apart as they move, and adults spend around 15 minutes a day grooming each other.

A siamang’s day starts at sunrise with the family’s morning song. Then the search for food begins, and it usually takes a siamang about five hours to eat its fill. After eight to ten hours on the move, the family settles in to rest and sleep. Siamangs sleep sitting upright in the fork of a tree.

The male and female mark their territory by singing a duet together. A family defends about 60 percent of its range as its own territory, and the song is the warning to neighbors.

Sources: Smithsonian’s National Zoo; Animal Diversity Web (University of Michigan).

Long arms: up to two and a half times the length of the body
Throat sac: inflates to the size of a grapefruit to power their calls
No tail: like all apes
Family territory: about 60 acres of forest, defended by song

A siamang hanging from overhead bars beside a yellow enrichment ball at Plumpton Park Zoo — A siamang stretches across the overhead bars. Photo: Nicholas Lacovara.

On the menu

What siamangs eat

Siamang gibbons feed on fruit, leaves, flowers, seeds, tree bark, as well as insects, spiders, bird eggs, and small birds.

In the wild, they spend about as much time eating leaves as eating fruit: about 44 percent of feeding time on fruit and 45 percent on leaves. That is a far higher share of leaves than any other gibbon eats.

Because siamangs eat so much fruit and travel through the forest, they are likely important seed dispersers, helping the rainforest regrow.

How does an ape digest all those leaves? Siamangs have a large, simple stomach like ours, not the multi-chambered stomach of leaf-eating monkeys. The work happens further down: their colon is slightly enlarged, and bacteria there ferment the tough plant fiber into fatty acids the siamang absorbs for energy. That makes them hindgut fermenters, on a modest scale, much like orangutans.

A Halloween treat at Plumpton Park Zoo.

Sources: Smithsonian’s National Zoo; Animal Diversity Web (University of Michigan); AZA Gibbon Care Manual, Nutrition chapter.

Family life

Raising a young siamang

Katya, an adult siamang, holding her baby Kazoo close against her chest at Plumpton Park Zoo — Katya and Kazoo at Plumpton Park Zoo. Photo: Nicholas Lacovara.

~7½ mopregnancy

1baby every two or three years

6–7 yrsto reach adulthood

A siamang family is an adult pair and their young. A baby weighs about 1.2 pounds at birth and clings to its mother’s belly constantly for the first three to four months. Twins sometimes occur, but one baby is the rule. Babies are weaned at 18 to 24 months.

Siamang fathers are unusually involved. In the youngster’s second year, the father takes over much of its daily care and carries it. Young siamangs stay with their family until they are grown, then leave to start their own. A female rarely has more than ten babies in her lifetime.

Sources: Smithsonian’s National Zoo; Animal Diversity Web (University of Michigan); Handbook of the Mammals of the World, vol. 3 (2013); Primate Info Net (Wisconsin National Primate Research Center).

Spot the difference

Siamang, gibbon or monkey?

Siamang

The largest gibbon. All black, with a big inflatable throat sac and the loudest song of any gibbon.

Other gibbons

Smaller relatives in the same family, such as lar and white-cheeked gibbons.

Orangutan

A great ape that also lives on Sumatra, much larger and heavier than any gibbon.

Monkeys

Most monkeys have tails. Siamangs, like all apes, do not.

Conservation

Why they matter

ENDANGERED

Siamangs are listed as Endangered. Their numbers have fallen by about half over the past 40 years. The main threats are loss of rainforest habitat to logging and palm oil plantations, and the illegal pet trade, in which adults are often killed so a baby can be taken and sold as a pet. Only about 4 percent of the siamang’s habitat is protected.

Sources: Smithsonian’s National Zoo; Animal Diversity Web (University of Michigan); New England Primate Conservancy; Malaysia Biodiversity Information System.

Close-up portrait of a siamang at Plumpton Park Zoo — One of our siamangs at Plumpton Park Zoo.

Support

Help care for our siamangs & the animals of Plumpton Park

As a nonprofit zoo, Plumpton Park Zoo relies on admissions, memberships and the generosity of people who believe in what we do. Donations help support animal care, veterinary services, nutritious diets, enrichment, habitat improvements and the continued development of the zoo.

Support Our Animals

Plumpton Park Zoological Gardens, Inc. is a 501(c)(3) nonprofit organization. Donations support the zoo’s charitable mission and are tax-deductible to the extent permitted by law.

Questions

Questions visitors ask about siamangs

How far can you hear a siamang?

Their whooping calls can carry for up to two miles through dense rainforest.

Why do siamangs sing?

To mark their territory and to strengthen the bond between mated pairs, who often sing together each morning.

Do siamangs have tails?

No. Like all apes, they have no tail.

Is a siamang a monkey?

No. A siamang is an ape, the largest of the gibbons. Monkeys usually have tails; apes do not.

What do siamangs eat?

Mostly fruit and leaves, plus flowers, seeds, bark, insects, bird eggs and small animals.

How do siamangs digest leaves?

They have a simple stomach like ours. Bacteria in a slightly enlarged colon ferment the plant fiber, so siamangs are modest hindgut fermenters.

How big is a siamang’s throat sac?

When inflated it can reach about the size of a grapefruit.

How far can a siamang leap?

They have been known to leap over 30 feet in a single jump.

How many siamangs live at Plumpton Park Zoo?

Five: Jack, Jocko, Katya, Kazoo and SongKhla.

Where can I see a siamang in Maryland?

At Plumpton Park Zoo in Rising Sun, Cecil County, Maryland. See Hours and Tickets for times and admission.

Hear Jack, Jocko, Katya, Kazoo and SongKhla at Plumpton Park Zoo

Our siamangs are part of a visit to Plumpton Park Zoo in Rising Sun, Maryland.

The zoo is in Cecil County, an easy drive from Delaware and southern Pennsylvania. While you are here, meet our ring-tailed lemurs, our two-toed sloths and our binturongs.

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