Gibbons are tree-swinging, small-bodied lesser apes not monkeys. They are the smallest of all apes; are found exclusively in Asia, mostly in India, Southeast Asia, Indonesia and to a lesser extent China; and live primarily in monsoon rain forests, mostly lowland forests. What distinguishes an ape from a monkey is the fact that the former doesn't have a tail. Gibbons are sometimes called “lesser apes.” The Dyak believe that gregarious people are kin to of gibbons and loners belong to the tribe of the orangutans.
Their scientific name for gibbons is “Hylobates” means “dweller in the trees.” "Compared to gibbons," Patricia Curtis wrote in Smithsonian magazine, "chimpanzees seem heavy and awkward, monkeys supple and frenetic and human athletes muscle-bound and slow. A gibbon is frequently a study in weightless, fluid motion. A gibbon swinging...and hurling itself to the ground to land like a feather is breathtaking to watch."
On the evolution of monkey-like creatures,David Attenborough wrote: “Another branch of its descendants spread eastwards into the forests of tropical Asia. There they took permanently to trees and developed their own special way of moving among the branches. They lost their tails and their arms elongated so that they could swing rather than clamber. Today they do so with such skill and astounding speed, that they are the most breathtakingly acrobatic of all tree-dwelling mammals. They are the gibbons.”
Gibbons live to the age of 20 or 30, with one captive animal living to be 44 years old. They differ from other higher primates in that they have a thumb that is free from the palm, giving it a wide range of movements.
Gibbons have a head and body length of 44 to 64 centimeters and no tail, and weigh between 4 to 8 kilograms. Attenborough wrote: “Feeding and traveling in the very top story of the forest, of course, limits an animal’s size. You can’t leap about at such speed from one tree to another in the way gibbons do if you are big and heavy. For one thing the branches would break.”
Gibbons are fruit eating primates. They mostly eat fruit but also eat leaves and a variety of insects, spiders, birds and eggs. There is not a great difference in size between males and females. They have very long their arms and have a low length to weight ratio, which is one reason why they are so acrobatic in trees. Their fur is brown, grey, white body and/or black and there is often a mixing of colors. Some have throat sacs that inflates during calls.
David Attenborough wrote: “Each species has its own characteristic coloration but they are all various combinations of brown or black usually with a white frame around the face. They have none of the bright colors or visual patterns common among monkeys for visual signals are not a very effective way of communicating between different groups of animals that are as widely dispersed as gibbons.
Gibbons and Trees
Gibbons spend much of their life in trees and have spectacular acrobatic skills. They can leap 10 meters from one tree to another, sit up erect as a man and run bipedally across the top of branches. The natural curvature of their fingers and toes helps gibbons swing rather than grip. Their arms are twice as long as their body, increasing their swinging ability further. Their big toes pivot both ways allowing them to grasp onto branches with both the front and the back of their feet.
Gibbons get around mainly by swinging hand over hand from branch to branch, using their hands like hooks and their arms like pendulums. Unlike monkeys which use their tails and arms to maneuver and jump from tree to tree, gibbons only use their long forearms to swing, not jump, pendulum-fashion in the upper canopy of the forest.
The progressive swinging by the arms of gibbons is called brachiation. Gibbons can cover three meters in a single swing. “A gibbon brachiating moves rhythmically, fast or leisurely, hand over hand from one horizontal support to another, arms fully extended, legs bent at the knee and relaxed---a stunning display of grace."
On the ground or large branches, gibbons walk upright, and in fact walk upright more than any other ape. They hold their arms out for balance when they walk and have a "comical, lurching bowlegged gait like a toddler learning to walk." They carry food when they walk along tree limbs. A few species can swim but most gibbons avoid the water and keep their stays on the ground to a minimum.
Gibbons are mostly diurnal. Typically, they are active about 10 hours a day, alternating between periods of feeding and rest. On average they move about one kilometer day, with more movement in the dry season and less in the wet season. Often sleeping in same tree, they make no home or nest but rather sleep on branches of a tree.
David Attenborough wrote: “They are the only primates, apart from human beings, who form permanent monogamous families, a male and a female with one, two or more rarely three of their young living closely together. These families seem to be closely-knit. In some species, members seldom move more than 25 yards away from one another. Gibbons will nibble leaves and occasionally catch insects which gives them valuable protein, but their main food is fruit...They need a large area to provide them with the quantity they require, so each gibbon family lays claim to its own extensive patch of forest.”
A mated adult pair and their offspring are the primary social unit. A typical group is made up of three or four individuals.. There are some solitary animals. They are usually young gibbons that have been forced out a family and have not formed a group yet. Juvenile gibbons may remain with their parents for five or six years until they reach sexual maturity. As they get old they periodically separate from their parents and begin looking and calling for mates.
Gibbons spend much of their time eating fruits and leaves, resting, grooming and playing with members of their family group. A group usually stays close together, with social bonds reinforced with considerable grooming. Some studies have shown that on average individuals in a group stay within eight meters of one another for the most part the entire day.
Family groups occupy a small stable home range and defend their territory. Most gibbons are fiercely territorial. An average territory is around 25 to 35 hectares. Defense methods include loud calls, the breaking of branches and physical contact. The spacing of territories is often defined through vocalizations.
Gibbon Calls and Songs
Many gibbons sing and make calls and have a large throat sac that enlarges when they make calls. Some of their calls are quite loud and can be heard up to eight kilometers away. For some species only the males have the large sacs. For others both males and females have them. Some don’t have pronounced sacs at all. The male siamang’s pouch balloons out as it sings and acts as a resonator.
All Gibbons sing. To qualify as a singer they have to repeat several series of notes in a recognizable temporal pattern. By one count only 14 other species in all of the animal kingdom sing. These includes a Madagascar lemur called the indris, the titi monkeys of South America and tarsiers (see Below).
The calls vary from species to species and also to a large degree form sex to sex and thus help to identify the callers. Group calls are often duets involving the adult males and females, sometimes with the backing from their offspring. The females produce the longest and most distinctive sounds. The female of one species, Kloss’s gibbon, produces a spectacular series of ascending pure notes leading into a bubbling trill.
David Attenborough wrote: “The song is usually repeated many times in the morning sessions that may last for up to a quarter of an hour. Different species have their own particular variant of this pattern and their own characteristic voices...The female in most species takes the major role with the male providing a coda at the end. In some species the pair duet, each with its own part. In others the two may sing in unison. The most accomplished singer is said to be the little pure black species, Kloss’s gibbon, that lives on the Mentawi islands off the west coast of Sumatra. Male and female sing by themselves. The female’s “great call” last for up to 45 seconds. It starts with a long series of pure, slowly ascending notes. Then she introduces trills that build into a bubbling crescendo. As her song rises to a climax, she leaps into the air and hurtles from branch to branch, tearing off sprays of leaves and throwing them to the ground. It’s a truly barn-storming performance.”
Ten of the twelve gibbon species sing duets. Pairs of siamang gibbons in Indonesia sing long duets of cascading calls, one after another for 15 minutes every other day. The duets are comprised of precise sequences of booming, barking and screaming that often take newly paired couples many months to learn. Scientists believe the calls are unrelated to bonding and mating but rather are used to define territories and intimidate rivals and intruders.
Gibbon Mating and Mothers
Males and females are difficult to distinguish from one another. Males reach sexual maturity around age six. At that time they begin looking for a mate. The female often does not reach full sexual maternity is until age eight or nine.
All species of gibbons are monogamous. Gibbons are thorough to mate for life. The male and female and their young are always together. Not much is known on how gibbons chose their mates. Animal behaviorist Janine Benyus wrote: "Females can be picky and...finding a compatible mate can be like dating in a very small town."
Gibbons give birth every two or three years and have a gestation period of about five months. Like all ape species, females ovulate about once a month and give birth to one infant at a time. Their young develop slowly, requiring years of maternal care and training."
Gibbons are said to be the best mothers in the entire animal kingdom. Young gibbons hold their mothers 100 percent of the time and don’t leave their mother’s completely until weaning is completed about one year and eight months after birth.
No one has ever observed a female gibbon let her offspring go until it has matured. Whether a mother is swinging through the trees, leaping from branch to branch, climbing up a trunk or scampering across the ground the young gibbon is always hanging onto her back.
There are up to 14 different species of gibbons living in the forests of Southeast Asia from eastern India through the Malaysian peninsula to Sumatra to Borneo. They include: 1) the crested (or concolor) gibbon of southeast China and northern Vietnam and Laos; 2) the siamang of peninsular Malaysia and Sumatra; 3) the white browed gibbon of Burma, Bangladesh, Assam and Yunnan; 4)the white-handed gibbon of Southeast Asia; 5) the dark-handed gibbon of southern Thailand, peninsular Malaysia and Sumatra; and Southeast Asia; 6) the capped (pileated) gibbon of southeastern Thailand and Cambodia; 7) the silvery gibbon of Java; 8) gray gibbon of Borneo; and 9) Kloss’s gibbon of some islands off Sumatra.
The gray gibbon is the most common of all gibbons. There are believed to be more than 1 million of them. The silver gibbon is the rarest. There are maybe only 3,000 of them left. Their original habitat has been reduced by about 96 percent. Most live in protected areas. White-handed gibbons live in family groups and mate for life. Four-month old babies about 20 centimeters in length and weigh about 900 grams. At birth they weigh about 120 grams. They clasp tightly to their mothers while growing up and become fully independent when they are about two years old.
The Silvery gibbon is critically endangered. The black gibbon is endangered. Threatened pileated gibbons have had their numbers reduced by poaching and loss of habitat resulting from farming. They survive in isolated areas of Thailand. About 50,000 are left.
Concolor gibbons have had their numbers reduced by poaching and loss of habitat resulting from farming. Males are black and females are golden or tawny brown. They survive in isolated areas of Laos, Vietnam and China. There could be as few as 10,000 are left. Animal behaviorist Janine Benyus wrote: "Females can be picky and, because the world's captive community is so limited, finding a compatible mate can be like dating in a very small town."
All 12 species of gibbon are on the endangered list. They are threatened by hunting and loss of habitat. Capturing and exporting them is banned everywhere. Breeding them in captivity is difficult because the world's captive community is very small and females are so picky about their choice of mates.
White-Handed and Dark-Handed Gibbons
The white-handed gibbon is one of the commonest gibbon species. It reaches 3½ feet in length, including the tail, and weighs between 8 and 12 pounds. It has a fringe of white hair around a black naked face and white-colored fur in the top of its hands and feet. Color varies from black to light buff with white hands. Males are often black. Females are often tawny or yellowish. There are about 200,000 of them.
Dark-handed gibbons vary in color from very dark brown to light buff, often with a reddish tinge. Males have white brows and cheeks, females have white eyebrows. There are about 600,000 of them.
The white-browed gibbons, also known as hoolocks, is India's only ape. Males are black with white eye brows and have longer hair than other species. Loud howls follow tree-top trills. There are about 100,000 of them.
Siamang and Pileated Gibbons
The siamang is the largest gibbon species. It has an arm span of 1.5 meters, a head and body length of 75 to 90 centimeters, no tail, and weighs between 8 to 13 kilograms. The body and limbs are black. It has a large gray or pink throat sac that inflates during calls and acts as a resonator. Its fur is longer and denser than other species. It eats more leaves than other species. Studies indicate their diet consists of 50 percent leaves and 40 percent fruit, with the remainder consisting of flowers, buds and insects. Some also eat leaves. There are about 150,000 of them.
Pileated gibbons live in tropical evergreen forests in southeast Thailand, and Cambodia west of the of the Mekong. There are 10,000 to 30,000 in Thailand. The number in Cambodia is unknown. It weighs 5 to 6 kilograms and it head and spidery body measure 44 to 63 centimeters. Males are black with white hands and feet and females are ash blond with a black cap and chest. At dawn mated pairs of pileated gibbon call to one another. Females release an "extended bubbly trill" that can be heard nearly two kilometers away.[Source: Canon advertisement in 2001 National Geographic]
Pileated gibbons have been bred using artificial insemination. About six months after birth babies are about the size of a human hand and weigh about 1,500 grams.
Image Sources: Wikimedia Commons
Text Sources: National Geographic, Natural History magazine, Smithsonian magazine, Wikipedia, New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, Top Secret Animal Attack Files website, The New Yorker, Time, Newsweek, Reuters, AP, AFP, The Economist, BBC, and various books and other publications.
Last updated November 2012