GIBBONS IN SOUTHEAST ASIA
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.
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).
Gibbons Found in Southeast Asia
Pileated gibbons (capped gibbons, H. pileatus) live in southeastern Thailand and Cambodia. They are endangered.
White-handed gibbons ( Lar 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..
Agile gibbon (black-handed gibbons, H. agilis) live in northern Sumatra and around the Thailand-Malaysia border. They are endangered.
Agile Gibbons: See GIBBONS IN INDONESIA factsanddetails.com
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PRIMATES: HISTORY, TAXONOMY, CHARACTERISTICS, BEHAVIOR factsanddetails.com ;
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Hoolock Gibbons
Hoolock gibbons (Hylobates hoolock) have a body length of 45-58 centimeters. Similar to black gibbons, they live in old growth tropical forests or secondary tropical forests and pick young leaves, fruit or catch small animals with their hands and eat young leaves of trees and bushes, fruits, insects and small birds. [Source: Center of Chinese Academy of Sciences, kepu.net]
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.
See Separate Article: HOOLOCK GIBBONS factsanddetails.com
White-Handed Gibbons
White-handed gibbons (Hylobates lar) are also known as Lar gibbons. One of the commonest gibbon species, with the largest latitudinal range of any gibbon, they in tropical rainforests in Indonesia, Laos, Malaysia, Myanmar, and Thailand. They used to live in China but are no longer found there. 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.Common in zoos, they live, on average, 30 years in the wild and up to 44 years in captivity. There are about 200,000 of them. [Source: Mariah Beaman, Animal Diversity Web (ADW) /=]
White-handed gibbons are found in dipteropcarp forests, lowland and submontane rainforests, mixed deciduous bamboo forests, seasonal evergreen forests, and peat swamp forests. Home territories ranges from 17 to 40 hectares. They live at elevations up to 1,200 meters and favor the high canopy of the forest, only rarely venturing to the understory or ground. They are primarily frugivorous (fruit eating), eating ripe figs and fruit from woody vines and tropical trees. They also eat leafy plants, flowers, and insects. They are picky eaters. Fruits are tasted and often discarded because they are over ripe or not ripe enough. The same food sources are returned to multiple times during peak season to eat the ripest fruit each time Food sources are also shared in overlapping territory areas.
White-handed gibbons range in weight from 4.4 to 7.6 kilograms (9.7 to 16.7 pounds) and range in length from 42 to 58.4 centimeters (16.54 to 23 inches). They either have a dark coat, which may range from gray to black to brown, or a light coat of light cream color to light brown They have a fringe of white hair around a black, hairless face and white-colored fur in the top of their hands and feet. Their elongated forelimbs, hands, and feet are adaptations for brachiation (swinging from tree limb to tree limb using their arms), which is their main way of getting around un the trees. Like other gibbons, they don’t have tails. Sexual Dimorphism (differences between males and females) is present: Males are larger than females. Males are 43.5 to 58.4 centimeters long and weigh 5.0 to 7.6 kilograms. Females are 42.0 to 58.0 centimeters long and weigh 4.4 to 6.8 kilograms. Males are often black. Females are often tawny or yellowish.
White-handed gibbons are currently listed as an endangered species on the International Union for Conservation of Nature (IUCN) Red List. On the US Federal List they are classified as Endangered. In CITES (Convention on International Trade in Endangered Species of Wild) they are in Appendix I, which lists species that are the most endangered among CITES-listed animals and plants. Their designation is in part due to the flourishing illegal pet trade in Thailand, in which they are hunted, captured and sold. Deforestation of their habitat is also a threat. Natural predators, especially for young, may include eagles, leopards, marbled cats, and pythons, but no act of predation has ever been observed.
White-Handed Gibbon Behavior, Communication and Reproduction
Hylobates gibbon species: 1) Western Hoolock Gibbon (Hoolock hoolock), 2) Eastern Hoolock Gibbon (Hoolock leuconedys), 3) Agile Gibbon (Hylobates agilis), 4) Bornean White-bearded Gibbon (Hylobates albibarbs), 5) Kloss’s Gibbon (Hylobates klossu), 6) Lar Gibbon (Hylobates lar), 7) Moloch Gibbon (Hylobates moloch), 8) Muller’s Gibbon (Hylobates muelleri), 9) Abbott's Gray Gibbon (Hylobates abbotti), 10) East Bornean Gray Gibbon (Hylobates funereus), 11) Pileated Gibbon (Hylobates pileatus)
White-handed gibbons are arboreal (live mainly in trees), motile (move around as opposed to being stationary), sedentary (remain in the same area), territorial (defend an area within the home range), and social (associates with others of its species; forms social groups). They sense using vision, touch, sound and chemicals usually detected with smell. Mariah Beaman wrote in Animal Diversity Web: White-handed gibbons are allo and auto-grooming animals. On average they spend ten hours a day allo-grooming. Auto-grooming is not significant proportion of daily activity. Allo-grooming probably serves more as a hygienic activity than a social function for this species. Fifteen and a half hours on average are spent in 'sleeping trees', from several hours before dusk until the following morning. This behavior reflects their adaptations to minimize predation risk. Vocal and physical interactions when retreating to sleeping trees are absent so as to avoid predator detection. Although this species is highly mobile, they do not gain safety during this stationary time period since they may fall asleep and not wake until a predator is upon them [Source: Mariah Beaman, Animal Diversity Web (ADW) /=]
White-handed gibbons generally live in family groups of two to six members. They use duets (joint displays, usually between mates, and usually with highly-coordinated sounds) to communicate. Normal duets are a function of territoriality; signaling to neighboring groups who pose a threat. Home ranges are defended during intergroup encounters and overlapping zones of ranges. Males sing together at range edges to chase away intruders and group defense becomes more important as home range size increases.
White-handed gibbons communicate using term songs, which are combinations of solos and/or duets (joint displays, usually between mates, and usually with highly-coordinated sounds) performed by bonded pairs. Calls are loud, long, and complex. Normal duets (joint displays, usually between mates, and usually with highly-coordinated sounds) are loud songs delivered by a mated pair that is made up of an introductory call, a great call, and an interlude sequence. The introductory call is a series of notes by the pair, followed by the great call which begins with the female to which the male answers back, and finally the interlude sequence which is variable, but consists of male and female notes and the male's answering call. Offspring aren't usually involved, but female offspring may sometimes perform a great call with her mother. Duets (joint displays, usually between mates, and usually with highly-coordinated sounds) occur between sunrise and noon, and peak at mid-morning. These calls average 11 minutes and can be heard up to one kilometer away The sound of their voice is the most common way to find gibbon groups. They are also detectable from their movement through trees or by plain sight, but these are much less common. /=\
White-handed gibbons are mostly monogamous (have one mate at a time) but sometimes engage in polyandrous activity (with females mating with several males during one breeding season). Monogamy is the norm among females who live in smaller home ranges where resources are denser; polyandry is seen in places where females live in larger home ranges and good resources are not numerous. White-handed gibbons breed once every 3.5 years., with the average number of offspring being one. The average gestation period is seven months and the average weaning age is 20 months. Females reach sexual or reproductive maturity at six to nine years. On average males reach sexual or reproductive maturity at nine years. Females care for young extensively. Males do not directly care for offspring.
In February 2021, the staff at Kujukushima Zoo & Botanical Garden in Nagasaki were shocked to find that Momo, a 12-year-old white-handed gibbon, gave birth despite being in a cage and not having a male mate. Following a DNA testing of the infant gibbon, the zoo learned that the father was Itō, a 34-year-old male gibbon who was held in an enclosure adjacent to Momo's. According to Nextshark: Although there is no surveillance footage for verification, the zookeepers believe that Momo and Itō were able to mate through a tiny hole measuring about 0.3 inch in diameter in a steel plate between their enclosures. The gibbons reportedly took turns going on display in the morning and afternoon in an exhibition area in front of Momo’s cage. “We think it’s very likely that on one of the days that Itō was in the exhibition space, they copulated through a hole,” a zookeeper said. [Source: Michelle De Pacina, NextShark, February 11, 2023]
Pileated Gibbons
Pileated gibbons(Hylobates pileatus) live in tropical deciduous monsoon forests, dense evergreens, and tall moist montane forests at elevations up to 1,500 meters (4,930 feet). They prefer old-growth forests with dense evergreen cover and avoid areas with patchy cover, exotic trees, trees taller than the primary canopy and other disturbances. Their range once extended from south Thailand to west of the Mekong in Cambodia, but now they are found only in southeast Thailand, extreme southwestern Laos, and northwestern Cambodia. The longest-lived Pileated gibbons in captivity survived 31 years. It is estimated that their average lifespan in the wild is 25 years.[Source: Canon advertisement in 2001 National Geographic; Rachel Cable, Animal Diversity Web (ADW) /=]
About 65,000 pileated gibbons remain in the wild in Thailand and Cambodia. On the International Union for Conservation of Nature (IUCN) Red List they are listed as Endangered. On the US Federal List they are classified as Endangered. In CITES (Convention on International Trade in Endangered Species of Wild) they are in Appendix I, which lists species that are the most endangered among CITES-listed animals and plants. Pileated gibbons have had their numbers reduced by poaching and loss of habitat resulting from deforestation, small-scale farming, logging and plantation agriculture for rubber and palm oil. Pileated gibbons have been hunted by humans for food, captured for the pet trade, studied as a possible source of hepatitis B, and bred using artificial insemination..
Pileated gibbons are mostly frugivorous (fruit eating), with soft-skinned or hard-rinded fruit making up 45 percent of their diet and figs making up 26 percent more. Figs are found in large patches and can be fed on for a longer period of time than other fruits, which are more dispersed. An additional 13 percent of the pileated gibbon’s diet is from young leaves and two percent is from unopened leaf shoots. They also consume insects (15 percent of total diet), eggs, and small vertebrates. Pileated gibbons spend more time feeding on fruit during the morning and evening, while leaves and insects are consumed more in the middle of the day. This pattern of behavior may be related to restoring energy lost during the previous night’ sleep and storing to the next night’s sleep. Pileated gibbons prefer to eat while sitting on branches in the middle and upper canopies.
Pileated Gibbon Characteristics
Pileated gibbons have slender torsos, long arms, no tail, and ischial callosities (thickened pads of tissue on the buttocks). Their head and body length ranges from 45 to 64 centimeters (17.7 to 25.2 inches) and they range in weight from four to eight kilograms (8.8 to 17.6 pounds), with their average weight being 5.4 to 5.5 kilograms. Both sexes are born covered in light buff-colored fur, with black spots on the top of their head and chest appearing at 10 to 12 months of age. These black spots grow continuously until sexual maturity. [Source: Rachel Cable, Animal Diversity Web (ADW) /=]
Sexual Dimorphism (differences between males and females) is present: sexes colored or patterned differently Males are black with white hands and feet and females are ash blond with a black cap and chest. According to Animal Diversity Web (ADW): Adult females have a large black patch from the top of the head to the groin on the ventral surface, which forms an inverted triangle. The rest of the body remains light gray or buff. The hair above the female’s ears is white, and is long enough to hang over the temples in characteristic “Dagwood tufts” by seven years of age. Sub-adult and young-adult females have a white brow band that decreases with age, pregnancy, or decreasing physical condition. Adult males are almost completely black with a narrow white face ring and crown ring as well as white hands, feet, and a genital tuft. Male hands and feet also have a fringe of hair halfway up their sides. Some males have lightly grizzled silver hairs on their legs and lower back.
As with most other species in the genus Hylobates, the hair on the ulnar side of the forearm grows in the direction of the elbow, while hair on the radial side grows in the direction of the wrist. Infant pileated gibbons have pink skin, which darkens with age and sun exposure, turning a light gray by adolescence and, eventually, a dark charcoal gray by the time they reach sexual maturity. Females often have adult fur by four years, while males have adult fur by 6.5 years. Both males and females have hairless facial areas and very dense fur elsewhere on their bodies. Neither sex has a laryngeal sac.
The teeth of Pileated gibbons have a distinct cingulum (shelf-like ridge around the outside of an upper molar) on the lingual side of the upper cheekteeth, a more lateral metaconid coupled with a more lingual hypoconid, and a comparatively large third molar. The skull morphology consists of a bowed zygomatic arch, downward pointing foramen magnum, and thick orbital rim. The dental formula of Pileated gibbons are 2/2, 1/1, 2/2, 3/3 = 32 and is common to all Hylobatidae.
Pileated Gibbon Behavior
Pileated gibbons are arboreal (live mainly in trees), diurnal (active during the daytime), motile (move around as opposed to being stationary), territorial (defend an area within the home range) and social (associates with others of its species; forms social groups). Their average territory size is 2.7 hectares (6.7 acres). Groups of pileated gibbons in Thailand’s Khao Soi Dao Wildlife Sanctuary have home ranges of approximately .36 square kilometers with .16 to .27 square kilometers of defended territory used exclusively by the group. Up to 6.5 groups per square kilometer have been reported found in old growth forests and up to three groups have been reported in one square kilometers of newer growth forests. [Source: Rachel Cable, Animal Diversity Web (ADW) /=]
According to Animal Diversity Web (ADW): Pileated gibbons spends about 8.2 hours per day resting (37 percent), with the remainder of the day consisting of feeding (26 percent), travelling (25 percent), grooming (5 percent), calling (4 percent), and playing (3 percent). The remaining 15.8 hours of the day are spent sleeping. Gibbons are social groomers, and intra-group rank determines who grooms whom, but little of the pileated gibbon's day is dedicated to grooming.
Pileated gibbons form small family groups consisting of a mating pair and young offspring. These groups occupy and defend a constant home range. At any one time, a single family group usually consists of one mating pair and two offspring of staggered ages, which eventually leave as additional offspring are born. Pileated gibbons travel through the trees mostly through brachiation (swinging from tree limb to tree limb using their arms). This form of locomotion, which can be very rapid, usually occurs in the upper and mid-canopies. Brachiation allows for large leaps of up to nine meters or more, with neither hand touching a branch. When on the ground, pileated gibbons are bipedal and hold their arms extended above the head for balance.
Pileated gibbons travel between 400 and 1300 meters (averaging 833 meters) in a single day with their family group. Sleep sites are usually centralized within the groups territory and generally consist of tall trees with few lower branches and vines. The same tree is rarely used more than once and almost never used on two consecutive nights. Characteristics common to sleeping trees most likely help reduce risk of predation, as well as decrease interactions with potential competitors. Pileated gibbons often sleep in trees that are close to the last feeding trees of that day. Intra-group individuals choose trees 10 to 15 meters apart, with infants sleeping with the mother and younger offspring sleeping in trees closer to the mother’s tree.
Pileated Gibbon Communication, Reproduction and Offspring
Pileated gibbons sense using vision, touch, sound and chemicals usually detected with smell. /=\ communicate with vision and sound. They also employ duets (joint displays, usually between mates, and usually with highly-coordinated sounds) and choruses (joint displays, usually with sounds, by individuals of the same or different groups to communicate). 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. Pileated gibbons couples announce their territories via a unique duet song. Females begin with a “great call,” and males joins midway through the great call with a series of shorter calls. The duet concludes with a single phrase of the males shorter call. The calling female also begins a locomotor display of brachiation and branch breaking during the song, sometimes accompanied by the male. The song pattern and tones of phrases used are unique to Pileated gibbons and are used as a conspecific identifier. Song bouts usually occur in the morning, with more recently established groups singing more often than older groups. Pileated gibbons sing least on rainy, cloudy, and windy days. [Source: Rachel Cable, Animal Diversity Web (ADW) /=]
Pileated gibbons are monogamous (have one mate at a time) and breed year round, with the average number of offspring being one. The testes of males descend late in the juvenile period, as is common with most species of gibbons. Pileated gibbon males have the shortest bacula (penis bones) of all gibbons. The estrous cycle of female pileated gibbons averages 27 to 30 days with a four to five day menstruation.
Average gestation lasts six to 7.5 months and most young are weaned between one and two years old. Infants stay with the mother until about age two, when they begin to move around independently. Females reach sexual maturity at around 7.5 years of age, and males do so between five and eight years of age. As with other gibbons, juvenile pileated gibbons remain with their family group and feed within the group's home range until sexually mature. As part of the effort to drive them from the group and territory, parents increase antagonism towards sub-adult offspring and prohibit them from mating. The age at which a sub-adult is driven out may depend on the size of the family group and resource availability.
Siamangs
Siamangs (Symphalangus syndactylus) are the largest of all gibbons. They live in tropical areas in forests and rainforests throughout the Barisan Mountains of Sumatra in Indonesia and in the mountains of the Malay Peninsula, south of the Perak River. They are mostly found in lowland, hill, and upper dipterocarp forests. There are two subspecies of siamang: the Sumatran siamang (S. s. syndactylus) and the Malaysian siamang (S. s. continentis), which occurs with other gibbons such as the agile gibbon and white-handed gibbon (lar gibbon). Siamangs They spend most of their time in the mid-upper canopy. Related gibbon species usually live into their 20s in the wild. Perhaps because they are larger, siamangs may not live as long as members of the gibbon species.[Source: Andrew Eastridge, Animal Diversity Web (ADW) /=]
Siamangs have an arm span of 1.5 meters (almost five feet), a head and body length of 71 to 90 centimeters (28 to 35.4 inches)., no tail, and weigh between 10 and 12 kilograms (22 and 26.4 pounds). Their body and limbs are black, and they have a large gray or pink throat sac that inflates during calls and acts as a resonator. Their fur is longer and denser than other gibbon species. The length of their slender arms may be 2.3 to 2.6 times the body length. Sexual Dimorphism (differences between males and females) is not present: Both sexes are roughly equal in size and look similar. Both sexes have long canine teeth, opposable thumbs, and a great toe that is deeply separated from the foot. Siamangs have a short-muzzled face that is nearly hairless, accompanied by a large brain case. They are syndactylous, which means their 2nd and 3rd toes are fused by a thin webbing of skin. Their most distinguishing characteristic is their sac which can be as large as a human head.
Siamangs are frugivores (fruit eating) and folivores (leave eating). They eats more leaves than other gibbon species. Studies indicate their diet consists of 43 to 48 percent leaves and 35 to 40 percent fruit, with the remainder consisting of flowers, buds, insects, bird eggs, and small vertebrates. During much of their feeding time they are suspended by one arm. Predation on these animals has not been thoroughly documented. It is likely that avian predators are a great risk to young. Carnivores and snakes may also prey upon Siamangs. /=\
There are as estimated to be between 150,000 and 300,000 siamangs, mostly in Sumatra, bust theyr are still listed as endangered,On the International Union for Conservation of Nature (IUCN) Red List they are listed as Endangered. On the US Federal List they are classified as Endangered. In CITES (Convention on International Trade in Endangered Species of Wild) they are in Appendix I, which lists species that are the most endangered among CITES-listed animals and plants. Siamangs are threatened mainly by deforestation and the destruction of their habitat for logging, small-scale agriculture and palm oil plantations. Siamangs are kept as pets, used in studies of primate behavior, and in entertainment. Some zoos have acrobatic siamang shows. Sometimes adults are killed and the babies are taken away for a trade. Only four percent of the siamang’s habitat is protected. /=\
Siamang Behavior
Siamangs are arboreal (live mainly in trees), diurnal (active during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area), social (associates with others of its species; forms social groups), and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates). Territory size depends on food supply and averages 11 to 38.4 hectares (28 to 95 acres), smaller than most other gibbons. [Source: Andrew Eastridge, Animal Diversity Web (ADW) /=]
Siamangs are highly territorial (defend an area within the home range). Males and females mark their territory vocally. According to Animal Diversity Web: 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. /=\
Locomotion is usually bipedal on the ground. In the trees the brachiate (using the arms to swing from branch to branch). 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 grabing the next, so that the body is freely projected through the air. Flights of eight to 10 meters have been witnessed. Siamangs, however, move less and and more slowly than most gibbon species.
Although its brain is highly developed, Siamangs does not appear to be very adaptable. Siamangs 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 eight to 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 minutes a 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. /=\
Siamang Communication, Reproduction and Offspring
Siamangs sense using vision, touch, sound and chemicals usually detected with smell and communicate with vision, touch and sound. They also employ duets (joint displays, usually between mates, and usually with highly-coordinated sounds) to communicate. Males and females mark their territory by singing a duet. [Source: Andrew Eastridge, Animal Diversity Web (ADW) /=]
According to Animal Diversity Web: 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 tume with each other and the male often swings through the trees during the song. The duets of mated pairs are very important in establishing territories and pair bonds. The neck sack of both sexes acts as a resonating chamber to amplify these calls, and makes siamangs look somewhat frog-like. All primates use visual signals, such as facial expressions, body postures and gestures in their communication. In addition to vocal communication, siamangs use tactile communication such as grooming and aggression.
Siamangs are monogamous (have one mate at a time) and engage in year-round breeding. Females typically give birth to one young every two to three years. Sometimes they take their time choosing mate, and do not usually take another mate if the first one dies. The gestation period of siamangs is around seven months and infants are weaned at 18 to 24 months. Females and males reach sexual or reproductive maturity at six to seven years. An individual female can give birth to as many as 10 offspring in her lifetime. Offspring cling to the mother's belly constantly for their first three to four months of life. Females nurse their young until they are about two years old. Males assist somewat in parental care by helping to defend young, defend the territory, and sometimes by grooming, playing with, or carrying the young. Older siblings may also help to rear younger siblings.
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