Class: Mammalia (Mammals)
Length: 29.5 to 35.5 inches (75 to 90 centimeters) from head to rump
Weight: 17 to 28 pounds (8 to 13 kilograms)
Life span: 25 to 30 years in the wild
Number of young: usually 1
Gestation: 7 to 8 months
Weight at birth: about 6 ounces (170 grams)
Age of maturity: 8 to 9 years
Conservation status: island siamang Symphalangus syndactylus syndactylus is endangered
siamang is the largest of the 16 species of gibbons.
A special throat sac enhances the siamang’s call, helping make it the loudest of the gibbons.
Siamangs can share territory with other gibbons because the siamangs are largely leaf eaters and do not compete for much of the forest fruit.
The siamang’s arm span is as wide as 4.9 feet (1.5 meters).
• Siamangs are one of the few primates known to form permanent pairs.
The siamang is in the same scientific family as gibbons and is well-suited for life in a forest’s treetops. Unlike great apes, siamangs do not build nests, because they sleep sitting upright on branches.
Their 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, the siamang hangs from a branch by one hand while swinging its body around to allow the other hand to grasp the next handhold. They 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.
Hands and feet
Siamangs’ hands are a lot like ours. They have four long fingers and a smaller opposable thumb. Their feet have five toes like we have, but their big toe is opposable too. One other thing that sets the siamang apart physically from the other species of gibbons is webbing between their second and third toes. Siamangs can grasp and carry things with both their hands and their feet. They have a small, round head, and their arms are longer than their legs.
Life among the leaves
Want to find a siamang in its forest home? Look up! They’re usually found in the trees at a height of 80 to100 feet (25 to 30 meters). 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 is inflated when they call out to others.
About half of the siamang’s diet in the wild consists of leaves; most of the rest is fruits, with flowers, buds, and insects added as well. The San Diego Zoo’s siamangs are fed leaf eater biscuits 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!
A typical day
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 4 to 6 p.m., the group settles in to a regularly used sleeping tree for the night. The closeness of the group is unusual among gibbons. A family of siamangs likes to stick together as they go about their daily business. During activities, group 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. A siamang 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 in age. Baby siamangs are born hairless except for a small tuft on top of the head. Infants can hold onto their mothers’ fur and cling to her belly soon after they’re born. The youngster is weaned early in its second year. 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. Young siamangs stay with their families for approximately five to seven years. Then they venture out on their own to start their own family group.
Can you hear me now?
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 the inflatable throat sac. These booming calls can be heard up to two 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 will usually start 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!