Symphalangus syndactylus
siamang

Symphalangus syndactylus is found throughout the Barisan Mountains of Sumatra (Indonesia) and in the mountains of the Malay Peninsula, south of the Perak River.

(Knight, 1997) (Nowak, 1999)

Siamangs are found in lowland, hill, and upper dipterocarp forest. They spend most of their time in the mid-upper canopy.

(Chivers, 1979; Preuschoft, 1990) (Nowak, 1999)

Symphalangus syndactylus is the largest of the gibbons, weighing between 10 and 12 kg. The head-body length ranges from 71 to 90 cm. They have a thick, black fur coat and long, slender arms. The arm length may attain 2.3 to 2.6 times the body length. Both sexes have long canine teeth, opposable thumbs, and a great toe that is deeply separated from the foot. Symphalangus syndactylus has a short-muzzled face that is nearly hairless, accompanied by a large brain case.

The most distinguishing characteristic of siamangs is the enlarged throat sac that can be as big as a human head! These throat sacs are used as a sound box to amplify their loud vocalizations.

Siamangs are syndactylous, having their 2nd and 3rd toes fused by a thin webbing of skin.

(Preuschoft, 1990; Chivers, 1979) (Nowak, 1999)

Related Hylobates species are known to have lived as long as 44 years in captivity. Because they are larger, siamangs probably do not live quite as long as other members of the genus. Lifespan in the wild is likely to be lower still. (Nowak, 1999)

Symphalangus syndactylus is highly territorial. The male and female mark their territory vocally by singing a duet. These calls usually begin with "dull, deep, bell-like tones," continues with a shattering, high yell followed by an overloud high-pitched laughter. The male and female partners sing in tume with each other and the male often swings through the trees during the song.

When an intruder (i.e. humans) enters their territory, the male confronts it while the female normally retreats out of sight. Intraspecific confrontations often involve high speed chases through the trees high off the ground, slapping and biting as they go. Both sexes participate in confrontations over boundaries.

Locomotion is usually bipedal on the ground. In the trees, these animals move by acrobatic hand-over-hand swinging through the branches, a process called brachiating. When moving slowly, they swing much like a pendulum as they grab one branch and let go of the previous one. When moving quickly, they often release the previous branch before grabing the next, so that the body is freely projected through the air. Flights of 8 to 10 m have been witnessed. Siamangs, however, move less and and more slowly than most gibbon species. They have smaller territories than other gibbons.

Although its brain is highly developed, S. syndactylus does not appear to be very adaptable. Siamangs wake at sunrise and perform their morning "concert". Then they set out in search of food. It usually takes a siamang about five hours to eat its fill. After about 8 to 10 hours of activity, it returns to its sleeping place.

One of the most important social activities of a siamang is grooming. Adults groom on average 15 min/day. Grooming is a display of dominance; the more dominant receives more grooming than it gives. An adult male grooms a female and sub-adult males. In the breeding season, he focuses more time on the female.

(Haimoff, 1983; Knight, 1997; Preuschoft, 1990; Chivers, 1979) (Nowak, 1999)

Home Range

Territory size depends on food supply, but an area averages 28 to 95 acres.

Two forms of communication used in this species have already been discussed. First, vocal communication, involving the morning duets of mated pairs, are very important in establishing territories and pair bonds. The neck sack of both sexes acts as a resonating chamber to amplify these calls, and makes siamangs look somewhat frog-like.

In addition to vocal communication, these animals use tactile communication. Grooming and physical aggression are two examples.

All primates use visual signals, such as facial expressions, body postures and gestures in their communication.

Symphalangus syndactylus survives mainly on leaves and fruit, but also eats insects, bird eggs, and small vertebrates. Symphalangus syndactylus eats a far higher proportion of leaves than any other gibbon (43 to 48 percent). During much of their feeding time they are suspended by one arm.

(Preuschoft, 1990; Chivers, 1979) (Nowak, 1999)

Predation on these animals has not been thoroughly documented. It is likely that avian predators are a great risk to young. Carnivores and snakes may also prey upon S. syndactylus. (Nowak, 1999)

As frugivores, these primates are likely to be important seed dispersers.

There are no known adverse effects of S. syndactylus on humans.

Symphalangus syndactylus has economic importance to humans. Siamangs are kept as pets, used in studies of primate behavior, and in entertainment. Many zoos display acrobatic siamangs for human enjoyment. (Nowak, 1999)

Although still fairly widespread, S. syndactylus is listed as endangered mainly due to destruction of their habitat for logging and agriculture. Also, many adults are killed so thay humans may have a pet baby siamang. Only 4% of their habitat is protected.

(Preuschoft, 1990) (Nowak, 1999)