ORDER: Primates

FAMILY: Hylobatidae

GENUS: Hylobates

SPECIES: syndactylus

Largest of the lesser apes. Height: up to 3 feet. Weight: 20 to 45 pounds (Sumatran male is largest). Color: jet black, with long, profuse, somewhat shaggy hair. Face is naked with sparse stubble of mustache and beard. Arm spread up to 5 feet. Forearm hair grows toward elbow as in great apes and man. Dark eyes, color vision and a throat sac inflatable to the size of the head. The toes are webbed between 2nd and 3rd toes. No facial fringe or tail.

Upper canopy of forested regions of Sumatra and the Malay Peninsula from 500 to 2500 feet.

Omnivorous. Fruits, leaves and other plant products. Probably small animals, insects, birds and birds' eggs.

Diurnal. They sleep upright in their small family group in tree foliage, unlike great apes who build nests or platforms for beds. Social group consists of a monogamous pair: one male, one female and up to 3 dependent offspring. Gestation: 7-8 months (230 days). Single births. Young are born very small (6 ounces) and usually naked. The long adult hair does not appear until 2-3 years of age. Infant is weaned at one year. When there are older youngsters in the family, the father gives the older ones protection and affection while the mother tends the infant. Siamangs mature at 6-8 years of age and at that time leave their parents. Lifespan: 25 years.

Well-developed forearms and limited body weight; use hands as hooks to facilitate brachiation. Carry objects with feet. Walk upright on ground with arms held above the head for balance. Rarely descend to earth. Inflatable throat sac acts as resonating chamber for vocal cords.

Hylobates means "wood-walker"; syndactylus refers to the webbing between the toes. Their loud calls usually occur only in the morning hours and are believed to help maintain territorial possession as well as cohesion within the siamang family group. The hooting-barking call can be heard for 2 miles. The songs have a definite pattern with repeatable sequences and a definite introduction, middle and end. It is called a great call duet, and the male and female each sing different parts.

The Siamangs can be found in the Tropical Rainforest. 2 Males. Both males were born here at the Oakland Zoo in 1996 and 1997.

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


  1. MacDonald, David. 1987. The Encyclopedia of Mammals, Equinox, Oxford.
  2. Nowak, Ronald. 1991. Walker
  3. Richard, Alison F. 1985. Primates in Nature. WH Freeman & Co.
  4. Shick, Alice. 1976. The Siamang Gibbons. Westwind Press, Milwaukee.