(Siamang, Great Gibbon)
Classification
•
Kingdom: Animalia
• Phylum: Chordata
• Class: Mammalia
• Order: Primates
• Family: Hylobatidae
• Genus: Hylobates
• Species: Hylobates syndactylus
Geographic Range
Neotropical: Hylobates 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)
Physical Characteristics
Mass: 10 to 12 kg.
Hylobates syndactylus is the largest of the gibbons with a head-body length of 29-35 in. They have a thick, black fur coat and long, slender arms. The arm length may attain 2.3 - 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. H. syndactylus have a short-muzzled face that is nearly hairless, accompanied by a large brain case. Their most distinguishing characteristic 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)
Natural History
Food
Habits
Hylobates syndactylus survives mainly on leaves and fruit, but also eats
insects, bird eggs, and small vertebrates. H. syndactylus eats a far higher
proportion of leaves than any other gibbon (43-48 percent). During much
of their feeding time they are suspended by one arm. (Preuschoft 1990;
Chivers 1979)
Reproduction
The gestation period in H. syndactylus is 230-235 days (7-1/2 months).
Females typically give birth every 2-3 years to one young, but twins sometimes
occur. The infant is weaned at 18-24 months and reaches maturity at about
6-7 years. An individual female rarely gives birth to more than 10 offspring
in her lifetime. Offspring cling to the mother's belly constantly for
its first 3-4 months. (Palombit 1995; Preuschoft 1990)
Behavior
Hylobates syndactylus is monogamous and highly territorial. It takes its
time in choosing a mate and does not "remarry" if the mate dies.
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 tune 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.
Their locomotion is usually bipedal on the ground. In the trees, they 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 grabbing the next, so that the body is freely projected through the air. Flights of 25-32 feet (8-10 m) have been witnessed. Siamangs, however, move less and slower than most gibbons. They have smaller territories than other gibbons.
Although its brain is highly developed, H. syndactylus does not appear to be very adaptable. They 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 8-10 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)
Habitat
The siamang is diurnal and arboreal. Territory size depends on food supply,
but an area averages 28-95 acres. Siamang are found in lowland, hill,
and upper dipterocarp forest. They spend most of their time in the mid-upper
canopy. (Chivers 1979; Preuschoft 1990)
Biomes:
tropical rainforest, tropical deciduous forest
Economic Importance for Humans
Positive
Hylobates sydactylus are beneficial to humans as pets, in studies of primate
behavior, and in entertainment. Many zoos display the acrobatic siamang
for human enjoyment.
Conservation
Status: endangered
Although still fairly widespread, Hylobates syndactylus is listed as
endangered mainly due to destruction of their habitat for logging and
agriculture. Also, many adults are killed so that humans may have a pet
baby siamang. Only 4% of their habitat is protected. (Preuschoft 1990)
References
Chivers, DJ 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.
Knight, T. 1997. http://www.selu.com/~bio/PrimateGallery/main.html
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