Symphalangus syndactylussiamang

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Geographic Range

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)

Habitat

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)

Physical Description

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)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    10 to 12 kg
    22.03 to 26.43 lb
  • Range length
    71 to 90 cm
    27.95 to 35.43 in

Reproduction

Symphalangus syndactylus is monogamous and highly territorial. Members of this species take their time in choosing a mate, and do not usually take another mate if the first one dies. (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)

  • Breeding interval
    Females typically give birth to one young every 2 to 3 years.
  • Breeding season
    Siamangs do not breed seasonally.
  • Range number of offspring
    1 to 2
  • Range gestation period
    230 to 235 days
  • Range weaning age
    18 to 24 months
  • Range age at sexual or reproductive maturity (female)
    6 to 7 years
  • Range age at sexual or reproductive maturity (male)
    6 to 7 years

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)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • male
      • female
  • extended period of juvenile learning

Lifespan/Longevity

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)

Behavior

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.

Communication and Perception

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.

  • Other Communication Modes
  • duets

Food Habits

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)

  • Animal Foods
  • eggs
  • insects
  • Plant Foods
  • leaves
  • fruit

Predation

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)

Ecosystem Roles

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

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

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)

  • Positive Impacts
  • pet trade
  • research and education

Economic Importance for Humans: Negative

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

Conservation Status

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)

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Andrew Eastridge (author), University of Michigan-Ann Arbor.

Glossary

acoustic

uses sound to communicate

altricial

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.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

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.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

duets

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

endothermic

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.

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

island endemic

animals that live only on an island or set of islands.

iteroparous

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).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

rainforest

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.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

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

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

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.