Gibbons are rare, small, slender, long-armed, tree-dwelling apes. These very acrobatic primates live in southeast Asia. Gibbons 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. There are nine species of gibbons, including the siamang, which is the largest and darkest gibbon. Because of the rapid deforestation of their habitats, gibbons are an endangered species.
ANATOMY
Gibbons 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. Gibbons have lightweight bones. Like all apes, they have no tail.
Hair:
Gibbons are covered with light-colored to very dark brown (or black) dense hair on most of their body (except their face, fingers, palms, armpits, and bottoms of their feet). Some species of gibbons have a white face ring, a band of white face completely surrounding their face.
Senses:
Gibbons have senses very similar to ours, including hearing, sight (including color vision), smell, taste, and touch.
Face:
Gibbons have a hairless face with dark eyes, small nostrils, and jet-black skin.
Hands and Feet:
Gibbons' 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. Gibbons 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).
SIZE
Male gibbons are slightly larger than the females. Males are about 3 ft (90 cm) long and weigh about 15 pounds (7 kg).
DIET
Gibbons are omnivores (eating plants and meat). 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.
Gibbons drink water, often by dipping a furry hand into the water or rubbing a hand on wet leaves, and then slurping up the water from their fur. Gibbons sometimes do this while dangling above the water from a thin tree branch.
BEHAVIOR AND SOCIAL HABITS
Groups of Gibbons:
Gibbons 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, gibbons less than 7 years old).
Grooming:
Like other apes, gibbons groom one another (they clean the hair of a family member).
Sleeping:
Unlike other apes, gibbons do not make "sleeping nests." They simply sleep (alone or with a few gibbons 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).
TERRITORIALITY AND VOCALIZATION
A gibbon family has a territory of about 30 to 50 acres of old-growth rain forest. Each morning upon awakening a family group of gibbons loudly announces its presence in the forest, using a territorial hooting call and menacing gestures. This call warns other gibbons 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.
The siamang, the largest and darkest species of gibbon, has an inflatable throat sac (called a gular sac). This sac can be inflated to be as big as the siamang's head. It acts a resonating chamber for the vocal chords, making the sounds even louder.
LOCOMOTION
Gibbons 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. Gibbons can also leap acrobatically across large gaps in the tree canopy from tree branch to tree branch; gibbons have been known to leap over 30 feet (9 m) in a single jump.
Gibbons cannot swim and avoid the water. When on the ground (which is rare), gibbons walk bipedally (on two legs).
LIFE SPAN
Gibbons live about 35-40 years.
HABITAT
Gibbons live in old growth tropical rain forests in southeast Asia.
DISTRIBUTION
The different species of gibbons live in different parts of southeast Asia, from China to the Malay peninsula, Burma, and North Sumatra.
REPRODUCTION AND BABY GIBBONS
Gibbon mates usually stay together for life. They are fully grown and able to reproduce at 12-13 years old. Female gibbons are pregnant for about 7 months and usually have a single baby at a time; twins are rare. Newborn gibbons are hairless except for a small cap of fur on the top of the head.
Female gibbons 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 gibbons stay with their mother for about 6 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
Gibbon populations are decreasing; they are threatened with extinction. Gibbons are losing their natural habitat because human agriculture is encroaching on it. Population numbers are decreasing. There are estimated to be about 79,000 lar gibbons (the white-handed or common gibbon).
THE EVOLUTION OF GIBBONS
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
Gibbons 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 11 living species of gibbons; since gibbons do not cross bodies of water, major rivers isolate each of the species.)
- Species H. agilus - the agile gibbon (or dark-handed gibbon)
- Species H. concolor - the crested gibbon (or the black gibbon)
- Species H. gabriellae - the red-cheeked gibbon
- Species H. hoolock - the Hoolock gibbon
- Species H. klossii - Kloss' gibbon (or Mentawai gibbon)
- Species H. lar - the white-handed gibbon or the common gibbon (consisting of three subspecies)
- Species H. leucogenys - the white-cheeked gibbon
- Species H. moloch - the Javan gibbon (or silvery gibbon, or white-browed gibbon)
- Species H. muelleri - the Bornean gibbon
- Species H. pileatus - the pileated gibbon (or capped gibbon)
- Species H. syndactylus - the Siamang (the biggest gibbon, with dark fur, an inflatable throat sac, and a very loud call)
GIBBON WEB LINKS
Lar gibbons from the Oakland Zoo.
The Gibbon Conservation Center, an organization devoted to the study and conservation of gibbons.
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