Siamang looks up tot he sky while touching his left ear with his hand, absentmindedly
Endangered

Siamang

Symphalangus syndactylus
Symphalangus syndactylus
  • CLASS: Mammalia (Mammals)
  • ORDER: Primates
  • FAMILY: Hylobatidae
  • GENUS: Symphalangus
  • SPECIES: syndactylus

ABOUT

Kings (and queens) of swing: Siamangs have slender bodies and lightweight bones for some serious swinging. These small, or lesser, apes are in the same scientific family as gibbons. Siamangs are the largest and darkest of the gibbon species and are well suited for life in a forest’s treetops. Yet there are some features on their hands and feet that make siamangs different from their gibbon brethren.

Siamang hands and feet are a lot like ours. They have four long fingers and a smaller opposable thumb on their hands, and their feet have five toes like we have, but their big toe is opposable, too. The opposable thumb and toe is lacking in other members of the gibbon family. Siamangs can grasp and carry things with BOTH their hands and their feet. One other thing that sets the siamang apart physically from other gibbons is webbing between their second and third toes.

HABITAT AND DIET

Life among the leaves: Want to find a siamang in its tropical forest home? Look up! They’re usually found in the trees at a height of 80 to 100 feet (25 to 30 meters) in Malaysia and Indonesia. How can you recognize them? Their furry bodies are black (both males and females), they don’t have tails, and they have a large gray or pink throat sac that inflates when they call. Unlike great apes, siamangs do not build nests, because they sleep sitting upright in the fork of a tree, usually alone but sometimes huddled together.

With arms that are longer than their legs, siamangs’ main way of traveling through the rain forest is by brachiation. The motion of their arms looks like the left-right motion of striding legs. During brachiation, siamangs hang from a branch by one hand while swinging their body around to allow the other hand to grasp the next handhold, just like you might do on a playground’s monkey bars. 

Siamangs are very acrobatic and agile. Their extra-long arms help them cover up to 10 feet (3 meters) in a single swing. If they’re not swinging through the trees, they’re very likely walking along branches with their arms outstretched to help them keep their balance.

More than half of the siamang’s diet in the wild consists of fruit. They also eat leaves and the occasional protein snack, which might include small birds or their eggs, spiders, and insects. 

The San Diego Zoo’s siamangs are fed biscuits made especially for zoo leaf eaters and a variety of fruits and vegetables such as oranges, apples, bananas, melons, grapes, yams, Romaine lettuce, spinach, turnips, carrots, and onions. They also get a selection of leafy material, including banana, hibiscus, and eugenia leaves. For a treat, keepers give the siamangs popcorn!

FAMILY LIFE

In the wild, siamangs might travel up to a mile (1.6 kilometers) in a day. And when they’re not swinging through the trees, travel is on dry land (siamangs cannot swim and avoid the water). On the rare occasions they do choose ground travel, they walk on two legs, holding their arms over their heads for balance. 

It’s early to bed for these tree dwellers! At around dusk, the family settles in to a regularly used sleeping tree for the night. The closeness of the family is unusual among gibbons. Siamang families like to stick together as they go about their daily business. During activities, members are only about 30 feet (10 meters) apart, on average, and rarely is one animal separated by more than 100 feet (30 meters). These social bonds are reinforced by lots of mutual grooming.

Siamang pairs usually stay together for life, one of the few primates to do so. When it comes to family life, siamangs stick together. A family group consists of one adult male and one adult female, along with two or three immature offspring that are only two or three years apart. A single baby is born hairless except for a small tuft on top of the head. The infant can hold onto the mother’s fur and cling to her belly soon after birth. 

The father does his share of raising the baby and takes over the daily care of the youngster when it is about one year old. This is unusual for most other primates. The youngster is weaned early in the second year. Young siamangs stay with their family for five to seven years. Then they venture out on their own to start their own family group. The newly independent siamang, male or female, begins to call and move separately from its parents and may spend several years looking for a mate.

Siamang calls are legendary. All gibbons can make amazingly loud sounds, and the siamang’s "song" includes booms and barks, made louder by an inflatable throat sac. These booming calls can be heard up to 2 miles (3.2 kilometers) away through the forest. The calls are used primarily for claiming territory, which can be as large as 50 acres (20 hectares). 

First thing in the morning, a family’s adult female usually starts a territorial hooting that the others join, and the noisy warning to other siamang families can last 30 minutes. Paired males and females also sing duets to one another, and each pair creates a unique song all their own!

AT THE ZOO

The San Diego Zoo received our first siamangs in 1928, and over the years we’ve welcomed 15 siamang babies. Today, we have Unkie, our adult male, and his mate of many years, Eloise. If there were an ape musical, Unkie would be the leading man. He arrived in San Diego from a zoo in Florida in 1986 at age 3. He and Eloise, who was born in a Northern California zoo in 1981, have been together since 1987 and can often be heard singing duets in harmony. Eloise, affectionately known as "Ellie," is the best mom a young siamang could hope to have. She's had lots of practice, having given birth to seven youngsters over the years. 

In 2003, a multilevel, naturalistic exhibit to house our siamangs and orangutans together was opened, as both species are native to the tropical rain forests of Sumatra. Keepers anticipated that the siamang family might have trouble initially fitting in with the much-larger orangutans, but the siamangs surprised everyone with their assertive behavior. Unkie is quite brave and enjoys harmlessly teasing the red apes, knowing his agility can quickly get him out of the way if need be. 

One of the enrichment opportunities in the exhibit is an artificial termite mound. It has long tubes inside it that open out on the surface, and keepers put in treats like baby food, applesauce, or barbecue sauce. The orangutans know how to use sticks as tools to dip into the holes to get the food, much as they would do in the wild to obtain termites, ants, and honey to eat. Although siamangs don’t tend to use tools in the wild, our siamangs learned to get the treats, too, just by closely observing their exhibit mates! Other enrichment for the siamangs and their friends include fresh browse, frozen “juice-sicles,” frozen fruit, and scattered foods like raisins that they can forage for throughout the day.

Siamangs are very smart, and our keepers have trained them to offer different behaviors that make taking care of them much easier. They can present their hands, feet, or mouth, which allows keepers and veterinarians to give them checkups without using anesthesia. They are also trained to go into a crate or get onto a scale to be weighed. Because they live with the orangutans, this is also helpful in making sure they are getting the right amount of food (Unkie seems to enjoy stealing the orangutans' food!).

Be sure to watch Unkie, Eloise, and their orangutan friends daily on Ape Cam.

CONSERVATION

Siamangs, like all gibbon species, are listed as endangered. The main reason for this status is loss of habitat due to logging and agriculture. Additionally, many adults are killed so their young can be sold into the illegal pet trade, even though siamangs are a protected species. San Diego Zoo Global supports the conservation initiative of Association of Zoos and Aquariums’ Ape Taxon Advisory Group.

One of the best ways to protect habitat for siamangs is by recycling here at home. Products like glass and aluminum are made from elements in the rain forest soil, and by recycling cans and bottles, we don’t need to dig as much in these threatened areas. Reducing paper use will also help, since many of the paper products we buy here in the U.S. come from trees cut down in Indonesia.

Save Wildlife. Help us keep this and other species from disappearing forever.

LIFE SPAN

25 to 30 years

YOUNG

Gestation: 7 to 8 months

Number of young at birth: Usually 1

Weight at birth: About 6 ounces (170 grams)

Age of maturity: 8 to 9 years

SIZE

Height: 29.5 to 25.5 inches (75 to 90 centimeters) tall, from head to rump; males are slightly larger than females

Weight: 17 to 28 pounds (8 to 13 kilograms)

FUN FACTS

Siamangs are one of the few primates known to form permanent pairs.

The siamang is the largest of the 14 gibbon species.

A siamang’s arm span is as wide as 4.9 feet (1.5 meters).

A special throat sac enhances the siamang’s call, helping make it one of the loudest of the gibbons.

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