Scientific Name:

Symphalangus syndactylus or Hylobates syndactylus

Common Name:

Siamang

Physical Descriptors:

Males range in head and body length of 46.8 to 84.6 cm and weighing from 9.5 to 12.7 kg, and females range from 46 to 63 cm in head and body length and weigh from 9 to 11.6 kg. Dental formula is: 2/2 1/1 2/2 3/3 = 32. 25 pair of chromosomes. First described by T.S. Raffles in 1821 as a new kind of gibbon. Larger than previously known gibbons, but similar in build. Coat is dense, long, shaggy, and all jet black except pale around mouth and chin with dark red on eyebrows. Forearm is elongated, long arms, long hands with less breadth of palm than other apes, and long feet. First toe is longest and strongest digit. Forearm hair grows toward elbow as in great apes and humans. Dark eyes and has color vision. Lack of earlobes. Index and middle fingers joined by a web of skin. No facial fringe or tail. They also have ischial callosites (sitting pads) normally found in monkeys, not apes. The male has a prominent preputal tuft of black hairs 15 cm in length. They live about 25 years. Reported to have the ability to change direction in mid-air. Inflatable neck pouch (laryngeal sac) in both males and females which can be blown up with air, and are the loudest of the gibbons. They have been heard calling in early morning and late afternoon with loud howls and shrill whistles interspersed with a booming sound of great resonance made by vocalizing into the laryngeal sac while keeping mouth closed, this can be heard for up to 2 miles. In captivity has been observed to sit quite still while vocalizing. The calls act to help maintain territorial possession as well as cohesion within the siamang family group. These have a definite pattern with repeatable sequences and a definite introduction, middle and end. The male and female will sing a "duet" with different but coordinated parts.

Geography:

Sumatra and Malay peninsula. Dwarf siamang on small islands of Sumatra.

Habitat:

Canopy of relatively undisturbed rainforests from 500 to 2500 feet. They prefer middle canopy but climb to crowns of trees or into low bushes to obtain food. They are arboreal and considered to use true brachiation as means of locomotion (arms for swinging in branches with hand over hand motion), and bipedal on larger branches. They walk upright on the ground, which is rare in the wild.

Food:

80% of diet is fruit such as figs, grapes and mangoes. Also eats leaves, insects, eggs and occasionally birds (which can catch in mid-air while swinging in branches). They often eat with one hand hanging onto a branch and reaching with the other.

Population Size:

Observed singly or in small family groups up to five in number (example: one male, one female, one infant and one or two juveniles). Male and female pair are monogamous. Lives in family groups with specific territory.

Reproductive Strategy:

Reaches sexual maturity at 5 to 8 years of age and will produce single offspring. Gestation period is 230 to 235 days with a birth weight of approximately 6 ounces. Newborn is usually naked and long hair does not appear until 2-3 years of age. Produces single offspring. Infant is usually carried by mother at first then hangs onto mother's chest. After weaning at approximately one year of age, the baby joins in the social life of family. The father will tend older children so that the mother can devote time to the infant. The young are unable to defend themselves until 3 to 4 years of age. They will reach full maturity at 8 years of age and leave the family.

Current Conditions:

All species of Hylobates are listed as endangered by USDI and are on appendix I of CITIES. Loss of habitat through agriculture has severely reduced their numbers.

References:

Primate Behavior, edited by Irven DeVore 1967 p.475

The Apes, by Vernon Reynolds 1967 p.57, 59, 62, 71, 90

A Handbook of Living Primates, by J R Napier and P H Napier 1967 p.4, 21, 22, 35, 316-319, 354, 377, 395, 408, 410-412, 415

The Marshall Cavendish International Wildlife Encyclopedia 1989 Volume 9, p.1027-30

The New Laraousse Encyclopedia of Animal Life 1967, p.512

Simon & Schuster's Guide to Mammals 1982, #118

Internet: The Oakland Zoo, Zoo Web Page, Animal Fact Sheet 1995

Return to the Hominoid page