The siamang is the largest and darkest species of gibbon. Siamangs are rare, small, slender, long-armed, tree-dwelling (lesser) apes. These very acrobatic primates live in southeast Asia.
Siamangs are arboreal; they spend most of their lives in trees. Because they are so dextrous while moving in the trees, almost no predators can catch them. The siamang is one of nine species of gibbons. The siamang is the largest, darkest, and noisiest species of gibbon. Because of the rapid deforestation of their habitats, gibbons are an endangered species.
ANATOMY
Siamangs are very small and lightweight. They have a small, round head, very long arms (the arms are longer than the legs), and a short, slender body. Siamangs, like all gibbons, have lightweight bones. Like all apes, they have no tail.
Hair:
Siamangs are covered with long, dense, shaggy, black hair on most of their body (except their face, fingers, palms, armpits, and bottoms of their feet). Siamangs are the darkest type of gibbon.
Senses:
Siamangs have senses very similar to ours, including hearing, sight (including color vision), smell, taste, and touch.
Face:
Siamangs have an almost hairless face; they have a slight mustache and beard. They have dark eyes, small nostrils, and jet-black skin.
Hands and Feet:
Siamangs' hands are very much like ours; they have four long fingers plus a smaller opposable thumb. Their feet have five toes, including an opposable big toe. Siamangs can grasp and carry things with both their hands and their feet. When they swing through the trees (called brachiating), they use four fingers of their hands like a hook (but they do not use the thumb for this).
Unlike other gibbons, siamangs have webbing between the 2nd and 3rd toes.
SIZE
Male siamangs are slightly larger than the females. Males are about 3 ft (90 cm) long and weigh about 15 pounds (7 kg). Siamangs have a reach of about 5 feet (1.5 m). Siamangs are the biggest type of gibbon and are the largest of the lesser apes.
DIET
Siamangs are omnivores (eating plants and small animals). They forage for food in the forests during the day, eating fruit (which constitutes about 75% of their diet), leaves, flowers, seeds, tree bark, and tender plant shoots. They also eat insects, spiders, bird eggs, and small birds.
Siamangs, like other gibbons, drink water. Often they drink by dipping a furry hand into the water or rubbing a hand on wet leaves, and then slurping up the water from their fur.
BEHAVIOR AND SOCIAL HABITS
Groups of Siamangs:
Siamangs are social animals that are active during the day (they are diurnal). They live in small, stable family groups consisting of a mated pair (a male and a female who mate for life) and their immature offspring (juveniles, siamangs less than 7 years old).
Grooming:
Like other apes, siamangs groom one another (they clean the hair of a family member using their fingers).
Sleeping:
Unlike other apes, siamangs and gibbons do not make "sleeping nests." They simply sleep (alone or with a few individuals huddled together) in a fork between branches. They sleep sitting upright, resting on tough pads located on their rear ends (these pads are called ischial callosities).
Throat Sac:
Unlike other gibbons, siamangs have a throat sac (also called a gular sac) which they can inflate to be about the size of their head. This sac makes their calls louder! Both males and females have a throat sac. The inflatable throat sac makes the siamangs the loudest of all the gibbons.
TERRITORIALITY AND VOCALIZATION
The siamang, unlike other gibbons, has an inflatable throat sac. This sac can be inflated to be as big as the siamang's head. It acts a resonating chamber for the vocal cords, making the sounds even louder. Their hooting can be heard up to 2 miles (6.5 km) away through the dense rain forest.
A siamang family has a territory of about 30 to 50 acres of old-growth rain forest. Each morning upon awakening a family group of gibbons very loudly announces its presence in the forest, using a territorial hooting call and menacing gestures. This call warns other siamangs to stay out of their territory (and especially away from the local fruit trees). This noisy display takes 1/2 hour or more every morning and is usually started by the adult female. The male and female have different calls.
LOCOMOTION
Siamangs are extremely acrobatic and agile. They spend most of their life in the trees. They move by swinging gracefully from branches and vines; this is called brachiating. When they brachiate, they use four fingers of their hands like a hook (but not the thumb). They can also walk along small branches high up in the air, like tightrope walkers; they use outstretched arms to help keep their balance. Siamangs can also leap acrobatically across large gaps in the tree canopy from tree branch to tree branch; siamangs have been known to leap over 30 feet (9 m) in a single jump.
Siamangs cannot swim and avoid the water. When on the ground (which is rare), siamangs walk bipedally (on two legs).
LIFE SPAN
Siamangs live about 35-40 years. They do not do very well in captivity.
HABITAT AND DISTRIBUTION
Siamangs live in the upper canopy (the tree tops) of tropical rainforests in Malaysia and Sumatra (in southeast Asia).
REPRODUCTION AND BABY SIAMANGS
Siamang mates usually stay together for life. They are fully grown and able to reproduce at 5-7 years old. Female siamangs are pregnant for about 8 months and usually have a single baby at a time; twins are rare. Newborn siamangs have much less hair than adult siamangs. Babies weigh only about 6 ounces at birth. This is less than the weight of a cup of water!
Female siamangs carefully nurture their young. Babies can grasp their mother's fur to cling to the mother's belly soon after birth. They are weaned at about 1 year old. Young siamangs stay with their mother for about 5-7 years. The young then venture out (or are forced out by the same-sex parent) to start a new family group of their own.
POPULATION COUNTS
All gibbon populations are decreasing, including the siamang. They are threatened with extinction. Siamangs are losing their natural habitat as human agriculture encroaches upon it and population numbers are decreasings.
THE EVOLUTION OF SIAMANGS
The earliest-known primates date from about 70 million years ago (Macdonald, 1985). The greater apes (family Pongidae, gorillas, chimpanzees, bonobos, and orangutans) split off from the lesser apes (family Hylobatidae, gibbons and siamangs) 20 million years ago. Gibbon-like fossils have been found in Africa (from the Oligocene and Miocene), Europe (from the Miocene), and Asia (from the upper Pliocene and Pleistocene).
CLASSIFICATION
Siamangs belong to the:
- Kingdom Animalia (all animals)
- Phylum Chordata
- Subphylum Vertebrata (animals with backbones)
- Class Mammalia (warm-blooded animals with fur and mammary glands)
- Order Primates (which is comprised of 11 families, including lemurs, monkeys, marmosets, lesser apes, great apes, and humans)
- Family Hylobatidae (meaning "tree dweller" - the lesser apes, including gibbons and siamangs)
- Genus Hylobates (with 9 species of gibbons; since gibbons do not cross bodies of water, major rivers isolate each of the species.)
- Species H. syndactylus - the Siamang (the biggest gibbon, with dark fur, an inflatable throat sac, and a very loud call)
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