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)
The gestation period in S. syndactylus is 230 to 235 days (7 months). Females typically give birth every 2 to 3 years to one young, but twins sometimes occur. The infant is weaned at 18 to 24 months and reaches maturity at about 6 to 7 years. An individual female rarely gives birth to more than 10 offspring in her lifetime.
(Palombit, 1995; Preuschoft, 1990) (Nowak, 1999)
Offspring cling to the mother's belly constantly for their first 3 to 4 months of life. Females nurse their young until the young are about two years old. Males assist in parental care in siamangs by helping to defend young, defend the territory, and sometimes by grooming, playing with, or carrying the young. Older siblings may also help to rear younger siblings. (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)
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)
As frugivores, these primates are likely to be important seed dispersers.
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)
There are no known adverse effects of S. syndactylus on humans.
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)
Nancy Shefferly (editor), Animal Diversity Web.
Andrew Eastridge (author), University of Michigan-Ann Arbor.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
union of egg and spermatozoan
an animal that mainly eats leaves.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats fruit
An animal that eats mainly plants or parts of plants.
animals that live only on an island or set of islands.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
Having one mate at a time.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
found in the oriental region of the world. In other words, India and southeast Asia.
the business of buying and selling animals for people to keep in their homes as pets.
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
breeding takes place throughout the year
Chivers, D.J. 1979. The Siamang and the Gibbon in the Malay Peninsula. Primate Ecology: Problem-Oriented Field Studies. John Wiley & Sons, New York.
Palombit, R. 1995. Reproduction of Wild Hylobatids. International Journal of Primatology. v. 16. Plenum Press, New York.
Haimoff, E. 1983. Occurrence of Anti-Resonance in the Song of the Siamang (Hylobates syndactylus). American Journal of Primatology. v.5. Alan R. Liss, Inc., New York.
Preuschoft, H. 1990. Lesser Apes or Gibbons. Grzimek's Encyclopedia of Mammals. v.2. McGraw-Hill, Inc., New York.
Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: The Johns Hopkins University Press.