GIBBONS: CHARACTERISTICS, BEHAVIOR, TREES, SONGS, MOTHERS

GIBBONS

white-cheeked gibbon

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" to distinguish them from the "greater apes" —humans, gorillas, chimpanzees and orangutans. The Dyaks of Borneo believe that gregarious people are kin to of gibbons and loners belong to the tribe of the orangutans.

There are 20 different species of gibbons living in the forests of Southeast Asia from eastern India through the Malaysian peninsula and eastward into China and southward to Sumatra, Borneo and Java. Their scientific name for most 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."

Fossil gibbons are known from the Miocene Period (23 million to 5.3 million years ago). The Hominidae family, which includes humans, orangutans, gorillas and chimpanzees separated from Hylobatidae (gibbons) about 18 million years ago. 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 are kept as pets and found in zoos around the world. Miles and Caldecott reported that Black-crested gibbons are kept as pets in Vietnam when infants are plucked from their mothers. As the infant enters adulthood they become a problem and are often abandoned by their owners. [Source: Tommy Boyd, Animal Diversity Web (ADW) /=]

Website: www.gibbons.de

Websites and Resources: Animal Diversity Web animaldiversity.org ; BBC Earth bbcearth.com; A-Z-Animals.com a-z-animals.com; Live Science Animals livescience.com; Animal Info animalinfo.org ; World Wildlife Fund (WWF) worldwildlife.org the world’s largest independent conservation body; National Geographic National Geographic ; Endangered Animals (IUCN Red List of Threatened Species) iucnredlist.org

Gibbon Characteristics

Hoolock gibbon

Gibbons have a head and body length of 44 to 64 centimeters (17.3 to 25.2 inches) and no tail, and weigh between 4 to 12.7 kilograms (8.8 to 28 pounds). Gibbons have extremely long arms and relatively long legs. The hands are so long that they appear hook-shaped. They differ from other higher primates in that they have a thumb that is free from the palm and comes out of the wrist, giving it a wide range of movements. The thumbs on the hands are not elongated and are not used for swinging from branch to branch; instead these thumbs are used more for grooming behavior. The body is generally held in an upright position. Gibbons live to the age of 20 or 30, with one captive animal living to be 44 years old. [Source: Erin Quist, Animal Diversity Web (ADW) /=]

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.

Phil Myers wrote in Animal Diversity Web: Their forearms are remarkably long, and both forefeet and hindfeet are long and thin. The forefeet have a deep cleft between first and second digits. The fur of these apes is usually black, gray, or brownish, often with white markings on hands, feet, and facial region. Ischial callosities (thickened pads of tissue on the buttocks) are present. Some gibbons and siamangs have an enlarged throat sac, which inflates and serves as a resonating chamber when the animals call. This structure is enormous in a few species, equalling the size of the animal's head. [Source: Phil Myers, Animal Diversity Web (ADW) /=]

The skulls of gibbon resemble those of hominids, with very short rostra, enlarged braincases, and large orbits that face forward. Gibbons are catarrhine primates; that is, their nostrils are close together and face forward and slightly downward. They lack cheek pouches and their stomach is not sacculated. Their teeth are similar to those of hominids. The molars are bunodont and lack lophs. The upper molars usually have a cingulum, which is sometimes large. The canines are prominent (more so than in most hominids) but not sexually dimorphic. The dental formula is 2/2, 1/1, 2/2, 3/3 = 32. /=\

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 are regarded as the best in the world at brachiation (swinging from tree limb to tree limb using their arms). According to Animal Diversity Web: Brachiation is an energetically advantageous mode of locomotion. It allows for relatively high speeds in the canopy and for jumps of 10 meters or more. When moving on branches or on the ground, gibbons walk on two legs (bipedalism), often using their arms for balance. [Source: Erin Quist, Animal Diversity Web (ADW) /=]

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. 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 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." It is also fast. It has been reportedly that gibbons can swing from branch to branch at speeds of up to 56 kilometers per hour (35 miles per hour).

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.

Gibbon Behavior

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. Gibbons often sleep in the tallest trees in an area as a defense against attacks from most terrestrial predators. They also sleep on branches with many twigs so that the twigs, which vibrate easily, will act as an early warning system. [Source: Rob Gregoire, Animal Diversity Web (ADW) /=]

gibbon (top) feet (left) and hands (right) compared to those of orangutans (2nd from top), gorillas (3rd from top) and chimpanzees (bottom)

All gibbon species have nuclear families consisting of a mated pair and zero to four dependent offspring. 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.

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.

Phil Myers wrote in Animal Diversity Web: Gibbons and siamangs are monogamous, living in small family troops of usually 2-6 related individuals. These groups are territorial (defend an area within the home range), maintaining their territories partly by conspicuous vocalization, which may involve loud duetting by group members. They are primarily vegetarian, feeding on figs and other fruit, leaves and shoots. They are remarkably active and agile brachiators, capable of exceeding 3m in a swing. Gibbons leap from branch to branch, sometimes travelling more than nine meters in a single leap. They also sometimes walk on large branches or on ground, assuming a bipedal stance with their arms raised for balance. Gibbons are active during the day. [Source: Phil Myers, Animal Diversity Web (ADW) /=]

Gibbon Calls and Songs

Gibbons are famous for their calls, songs and duets. They 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.

According to Animal Diversity Web: Gibbon groups produce loud, stereotyped songs in the early morning. Songs are thought to function primarily in defense of resources such as territories, food trees, and mates. However, songs may also help to attract potential mates. Gibbon songs include species-specific characteristics which are inherited rather than learned. [Source: Erin Quist, Animal Diversity Web (ADW) /=]

Siamang shout

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.

Much research has been done on the song of gibbons due to the important role it has in determining gibbon taxonomy. Research has shown that Borneo gibbons is able to identify other species of gibbons through song. [Source: Sandra Bruening and Sandra Bruening, Animal Diversity Web]

Gibbon Monogamy, Reproduction and Mating

male and female white-cheeked gibbon

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. How gibbons chose their mates is not known. Animal behaviorist Janine Benyus wrote: "Females can be picky and...finding a compatible mate can be like dating in a very small town."

Most but not all gibbons are monogamous (have one mate at a time). They were once thought to mate for life. Although in most cases that is true but not always. Exceptions include: 1) serial monogamy in which gibbons have more than one mate at a time; 2) Extra-pair copulations in which gibbons may copulate with other gibbons outside of their pair; 3) Divorce (gibbons occasionally "divorce" their partner); and 4) Flexibility. With the latter, some gibbons, like white-handed gibbons, are mostly monogamous but may, for example, they take a new mate if their partner dies. [Source: Wikipedia]

There is a difference between reproductive monogamy and social monogamy. Some gibbons may hang out with their mate much of the time but have a fling on the side. The breeding system of some gibbons, like crested gibbons, may be more flexible than previously thought. For example, a study found that 40 percent of crested gibbon offspring were sired by extra-group males.

Monogamy is found in only three percent of mammals thus the monogamy of gibbons is of interest to scientists. One theory to explain gibbon monagamy is that it is result of the female need for protection from a male while taking care of young. Monogamy may also be related to ecological factors such as food availability and range size. It has also been theorized that the female’s range defense songs which are often responses to range defense songs of other females helps maintain monogamy. [Source: Sandra Bruening and Sandra Bruening, Animal Diversity Web]

Gibbon Families and Mothers

Gibbons are altricial. This means that young are born relatively underdeveloped and are unable to feed or care for themselves or move independently for a period of time after birth. There is an extended period of juvenile learning. Most gibbon females nurse and care for their young for about two years. Because young typically stay with their parents, older siblings may help in care of younger siblings. Males are also usually active in defending the family’s territory and grooming young. [Source: Sandra Bruening, Animal Diversity Web (ADW)]

Gibbons give birth every two or three years and have a gestation period of about five to eight months. They don't give birth every year because they nurse their young for around two years and do not give birth when they are nursing, 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.

Classification of Gibbons

There are four genuses of gibbons: 1) Hylobates; 2) Hoolock (formerly Bunopithecus), 3) Nomascus and 4) Symphalangus. Each genus differs in the number of chromosomes and some have only been elevated to the genus level relatively recently. The classification of gibbons has undergone several several times in recent years. For a long time all gibbons were classified in the genus Hylobates, with the exception of the siamang. After some studies, the genus was divided into three subgenera (including the siamangs Symphalangus), and then into four (recognizing Bunopithecus as the hoolock subgenus distinct from other gibbon subgenera). These four subgenera were elevated to full genus status. [Source: Wikipedia]

A great deal of DNA and molecular research has been done recently on gibbon phylogeny (evolutionary history of a species or group of organisms, and the relationships between them) . Hookock, Hylobates, Symphalangus, and Nomascus are monophyletic groups. Members of Nomascus are characterized by having a diploid number of 52 chromosomes. Nomascus is found from southern China to southern Vietnam, and is found on Hainan Island. Fur coloration, anatomical data, and vocal data are also used to identify different species of gibbons. Within the subgenus Nomascus, there are four separate species that include black-crested gibbons, eastern black-crested gibbons, yellow-cheeked gibbons, and Northern white-cheeked gibbons, [Source: Tommy Boyd, Animal Diversity Web (ADW) /=]

The type species for Bunopithecus is Bunopithecus sericus, an extinct gibbon or gibbon-like ape from Sichuan, China. Very recent investigations have shown that the hoolock gibbons are not closely related to B. sericus, so they have been placed in their own genus, Hoolock. In the process, the two subspecies of hoolock gibbons have been raised to species level.

Hylobatidae

The genus Hylobates is the the most species-rich and widespread of gibbon genera, ranging from southern China (Yunnan) to western and central Java. Its name means "forest walker", fand is derived from Greek. It was once considered the only genus, but recently its subgenera (Hoolock Nomascus, and Symphalangus) have been elevated to the genus level. Individuals within this genus are characterized by 44 chromosomes and often have a ring of white fur around their faces. [Source: Wikipedia]

Lar gibbon or white-handed gibbons (H. lar) live in Indonesia, Laos, Malaysia, Myanmar, and Thailand. Their range historically extended from southwest China to Thailand and Burma south to the whole Malay Peninsula and into the northwest portion of the island of Sumatra.. There are five subspecies of lar gibbon: 1) Malaysian lar gibbon (H. l. lar); 2) Carpenter's lar gibbon (H. l. carpenteri); 3) Central lar gibbon (H. l. entelloides); 4) Sumatran lar gibbon (H. l. vestitus); and 5) Yunnan lar gibbon (H. l. yunnanensis). They are endangered.

Gibbons Found in Borneo:
Bornean white-bearded gibbons (H. albibarbis) live in southwest Borneo in Kalimantan in Indonesia. They are endangered.
Western grey gibbons (Abbott's grey gibbons (H. abbotti) live in northwest Borneo mainly in Sarawak in Malaysia. They are endangered.
Eastern grey gibbons (northern grey gibbons, H. funereus) live in northern Borneo. They are endangered.
Müller's gibbons (southern grey gibbons, H. muelleri) live in southeast Borneo in Kalimantan in Indonesia. They are endangered.

Gibbons Found in Indonesia and the Malay Peninsula:
Silvery gibbons (H. moloch) live in Java. They are endangered.
Kloss's gibbons (Mentawai gibbon or bilou, H. klossii) live in the Mentawai west of Sumatra. They are endangered.
Agile gibbon (black-handed gibbons, H. agilis) live in northern Sumatra and around the Thailand-Malaysia border. They are endangered.
Pileated gibbons (capped gibbons, H. pileatus) live in southeastern Thailand and Cambodia. They are endangered.

Nomascus

Nomascus is the second-most species-rich genus of the gibbon family. Formerly it was a subgenus of Hylobates, with all individuals considered to be one species, H. concolor. Species within Nomascus are characterized by 52 chromosomes. Some species are all-black, some are a lighter beige or peach hue, with a distinct black tuft of crown fur, while others have notable, light-colored cheek “patches”. Nomascus are found in southern China (Yunnan), Vietnam, and China’s Hainan Island. [Source: Wikipedia]

Black crested gibbons (Nomascus concolor, Harlan, 1826) live in China, Laos, and northern Vietnam. There are four subspecies: 1) Tonkin black crested gibbon (Nomascus concolor concolor); 2) Laotian black crested gibbon (Nomascus concolor lu); 3) Central Yunnan black crested gibbon (Nomascus concolor jingdongensis; 4) West Yunnan black crested gibbon (Nomascus concolor furvogaster). They are critically endangered.

Nomascus in China:
Hainan black crested gibbons (Nomascus hainanus, Thomas, 1892) live in Hainan Island, China. They are critically endangered.

Nomascus in Vietnam, Laos and Cambodia:
Eastern black crested gibbons (Nomascus nasutus, Künckel d'Herculais, 1884) live in northeast Vietnam. They are critically endangered.
Northern white-cheeked gibbons (Nomascus leucogenys, Ogilby, 1840) live in northern Vietnam and northern Laos. They are critically endangered.
Southern white-cheeked gibbons (Nomascus siki, Delacour, 1951) live in Vietnam and Laos.. They are endangered.
Yellow-cheeked gibbons (Nomascus gabriellae, Thomas, 1909) live in Vietnam, Laos, and Cambodia. They are endangered.
Northern buffed-cheeked gibbons (Nomascus annamensis Thinh et al., 2010 live in Vietnam, Cambodia, and Laos.. They are endangered.

Hoolock and Siamang

The hoolock genus contains three species all with Hoolock in their name. Native to eastern Bangladesh, Northeast India, Myanmar, and Southwest China, they are the second-largest of the gibbons, after the siamang. They reach a size of 60 to 90 centimeters and weigh six to nine kilograms.

Western hoolock gibbons (Hoolock hoolock, Harlan, 1834) live in India, Bangladesh, and Myanmar. They are endangered.
Eastern hoolock gibbons (Hoolock leuconedys, Groves, 1967) live in China (Yunnan). They are vulnerable.
Skywalker hoolock gibbons (Hoolock tianxing, Fan et al., 2017) live in Myanmar and southwestern China. They are endangered. There are only 150 of them.

Siamangs (Symphalangus syndactylus) are the only species in the genus Symphalangus. Fossils of siamangs date back to the Middle Pleistocene. The siamang lives Indonesia, Malaysia, and Thailand. It is the largest species of gibbons — up to twice the size of other gibbons — reaching one meter (3.3 feet) in height, and weighing up to 14 kilograms (31 pounds).

Image Sources: Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated December 2024