Lee Richardson Zoo


Order:  Primates
Super Family – Hominoidae – apes and man
Family:  Hylobatidae - gibbons

Scientific Name: Symphalangus syndactylus


Description:  Average 3 ft. tall.  Arm spread is 5 ft.  Weigh 17-28 lbs.  Long, silky, black hair; no hair on face.  Forehead is low.  Nose is broad.  Canine teeth are formidable for attack.  Excellent vision.  Cup-shaped hands for gripping, thumb extends from wrist.  Strong legs; uses back legs to walk upright.  Second and third toes are webbed (only gibbon with this trait). Throat sac; enlarges to amplify call.  Call is used to define territory; female barks, male screams.  Rump has calluslike pads.  No tail. 

Home Range:  Sumatra and Malaysia.


Habitat Type:  Rainforest with home range up to 100 acre tracts.


Reproductive Habits:   The siamang mates for life.  After a 7-8 month gestation  period, a single baby is born. For the first year of its life, the baby is fed and cared for only by its mother.  Then the father takes charge of its education, although the mother continues to feed it for another year.  At age six the youngsters become sexually aware and seek out mates.  The young male will avoid its mother, so as not to anger its father.  At age eight it moves out to start its own family.  Because of the long period of parental care, the siamang produces only one offspring every two to three years.  


Diet in Wild:  Leaves, ripe fruit, particularly figs, insects and bird eggs.


Diet in Zoo:  High protein monkey biscuits, Zupreem high protein leaf eater diet, apples, carrots, and other available seasonal produce.


General Info: The siamang is the largest of the nine gibbon species, and therefore is less graceful than smaller gibbons.  As suggested by its scientific name Hylobates, meaning “dweller in the trees”, gibbons exceed all other animals in agility.  Siamangs are highly adapted for a life in the tree tops, and the only primate (besides man) to walk upright when they descend to the ground.


The siamang travels rapidly through the trees by moving arm over arm or swinging from branch to branch.  With arms 1/3 longer than their body, they can cover nearly 10 ft. in a single swing.  Siamangs walk along the branches if they are too large to grip with their hook shaped hands.  When siamangs stand erect, their arms dangle on the ground, so they hold their arms over head to keep them from dragging on the ground, and for balance.  At night the siamang sleeps sitting upright high in the branches of the trees in the center of its range.  The pads on its rump help it rest more comfortably.  


Siamangs live in a small, close knit family group consisting of an adult male and female and two or three youngsters.  Grooming is a major social activity that strengthens the family bond.  A siamang family occupies a home range of up to 100 acres.  Family members seldom need to travel more than a mile to get food. 

The siamang feeds during the day.  Siamangs dislike water, and cannot swim.  To drink, they cup water in their large hands.  


Although all gibbons call to each other, the siamangs call is the loudest and can be heard two miles away.  They are especially noisy at dusk and dawn.  Its large throat sac, which can be inflated to almost the size of its head, helps to amplify the call.  A male and female pair sing in unison, and at the start of the song the young join in.  The song reaches its climax with the great call of the female.  Calling serves to announce and reinforce territories, especially to establish eating and sleeping trees, and to develop the bond between male and female. 
A quieter group will give way to a louder group.


Conservation Status:  Siamangs are listed as Endangered on IUCN Red List and Appendix l of CITES.  They are suffering severe losses due to an increase in human population, hunting and habitat destruction from logging and agriculture.  All gibbon species are rapidly declining in numbers.  Unless the destruction of their rainforest home stops, many more species will become endangered.



Wildlife Fact File.  Group 1: Mammals.  Card # 127.   1991.


Walkers Mammals of the World.  Vol. 1.  R. Nowak.  The Johns Hopkins University Press.  Baltimore and London.  1991.  pp. 493. 

Monkeys and Apes.  P. Napier and Prof. J. Napier.  Time-Life Films. 1976.  pp. 52-58.


Grzimek’s Animal Life Encyclopedia.  Vol. 10. Dr. H.C. Bernhard Grzmek.  Van Nostrand Reinhold Co., New York, N.Y.  pp. 478-481.


The Collins Guide to the Rare Mammals of the World.  J.A. Burton and B. Pearson.  The Stephen Green Press.  Lexington Mass. pp.  84-85.