GIBBONS IN INDONESIA AND BORNEO

GIBBONS IN INDONESIA

silvery 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.

Gibbons Found in Indonesia
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.

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.

White-handed gibbons or 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.. 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.

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).

Silvery Gibbons

Silvery gibbons (Hylobates moloch) are endangered primates that live on the western half of the island of Java in Indonesia. They live in tropical rainforests and semi-evergreen rainforests, preferring the upper canopy of the lowland and hill forests up to an elevation of 2,450 meters (8,040 feet). They spend most of their lives in trees, and rarely descend to the ground. [Source: Jennifer Kuester, Animal Diversity Web (ADW) /=\, Wikipedia]

Silvery gibbons range in weight from four to nine kilograms (8.8 to 19.8 pounds), averaging around eight kilograms. Sexual Dimorphism (differences between males and females) is not present: Both sexes are roughly equal in size and look similar. Both male and female are a silverly-gray color and possess a dark gray cap. They have long arms and lean bodies, both of which help them maneuver through the canopy of the rainforest by brachiation (swinging from tree limb to tree limb using their arms).

silvery gibbon range

Silvery gibbons are primarily frugivores (fruit eaters) but are also considered herbivores (primarily eat plants or plants parts). Among the plant foods they eat are leaves, fruit and flowers. Like other gibbon species they like to feed on ripe fruits in the upper canopy of the tropical rainforests. Being fruit-eating) presents certain problems as fruit patches are found in small, scattered areas throughout the rainforest and sometimes these may be difficult to reach due to the fragmented nature of their habitat. Otherwise, brachiation helps the gibbons travel rapidly and efficiently from one food source to another.

In 2008 the International Union for Conservation of Nature (IUCN) estimated there were 2,500 mature silvery gibbons left in the wild. One the IUCN Red List these gibbons are listed 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. /=\

The biggest threat to gibbons is deforestation of the tropical rainforests. Habitats are disappearing at an astonishing rate due to logging and agricultural demands. There are not many quality rainforests left in Java. Reserves and parks encompassing the gibbon’s habitat have been established but no conservation programs specifically geared for silvery gibbons have been set up. They may also be hunted for meat, and illegally poached for the pet trade.

Silvery Gibbon Behavior, Communication and Reproduction

Silvery 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). They live in relatively small territories of about 17 hectares (42 acres). Gibbon groups are typically small, consisting of a monogamous pair, an infant and a juvenile, making the average group size about four individuals. /=\

Silvery gibbons sense using vision, touch, sound and chemicals usually detected with smell and communicate with vision, touch and sound. They employ and calls and duets (joint displays, usually between mates, and usually with highly-coordinated sounds) to communicate. In addition to vocalizations, gibbons use facial expressions and body postures in communication. Tactile communication is of some importance between mates, as well as between parents and their offspring. /=\

Mated pairs use duets to mark their territory and announce their presence to members of their own species. According to Animal Diversity Web: They are highly territorial and defend their territories by "singing." These loud calls can often be heard up to a kilometer away. Both male and female silvery gibbons call during territorial disputes. During these disputes, the female calls loudly, a "great call" and scream, while the male approaches the intruder and chases it away.

The majority of the solo song bouts or scream bouts are produced by females. Females sing to declare their territory several times a day. The female vocal bouts occur after around 5:00am and peak around 6:00am. Male vocalization primarily occurred before 5:00am, usually created in the style of a chorus, with a minimum of three participants. There are choruses around every 8.5 days that take place sooner and lasted longer than female solo song fights. The majority of male songs begin in the dark, between 3:55am and 4:40 am. Males are usually very aggressive toward others. [Source: Wikipedia]

Gibbons are typically monogamous (have one mate at a time). Silvery gibbons engage in year-round breeding and employ sexual induced ovulation (release of a mature egg from the ovary). The interbirth period of a reproductive female is about 40 months. There is no defined breeding season. The average number of offspring is one. A mated gibbon pair will produce an average of five to six offspring over their reproductive lifespan of about 10 to 20 years. The average gestation period is seven months. Most female gibbons nurse their offspring until the offspring are about two years old. Offspring leave their natal group when they become sexually mature.

Agile Gibbons

male agile gibbon

Agile gibbons (Hylobates agilis) are also called the black-handed gibbon and dark-handed. They are mainly found in tropical rainforests. on the island of Sumatra in Indonesia but are also found forests in the border region of southern Thailand and northern peninsular Malaysia. Prefering the upper canopy of the forest, where they feed and sleep, they spend most of their lives in the trees, and rarely descend to the forest floor. Agile gibbons are primarily frugivorous (fruit eating). The consumes large amounts of fruits but also been observed eating other foods such as leaves, flowers, and insects. Due to their active lifestyle, it is necessary for them to eat food rich in calories, which fruits are. Their average lifespan in the wild is estimated to be 25 years based on similar species.[Sources: Wikipedia, Jennifer Kuester, Animal Diversity Web (ADW) /=]

There are estimated to be around 600,000 agile gibbons but they 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. The main threats to them are deforestation and degradation of their forest habitat due to logging and agricultural demands, particularly by small farmers and palm oil agriculture. They may also hunted by humans for meat and folk medicine. Conservation measures have been included setting up reserves and parks and establishing breeding programs in zoos. Natural predators, especially to young, may include raptors and large snakes.

Agile gibbons range in weight from four to six kilograms (8.8 to 13.2 pounds) and have a head and body length of 44 to 63.5 centimeters (17.3 to 25 inches). They vary in color from very dark brown to light buff, often with a reddish tinge, but also can be black or reddish-brown. Sexual Dimorphism (differences between males and females) is present: Males are larger than females and have different colorations. Both sexes have white eyebrows. Males and females can be easily distinguished by the white brows and cheeks of the males; females have white eyebrows. Like other gibbons, Agile gibbons have long arms and fingers that serve as aids in brachiation (swinging from tree limb to tree limb using their arms), the prnciple mean of locomotion for these animals.

Agile Gibbon Behavior

Agile 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), 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 and communicate with vision, touch and sound. They also employ duets (joint displays, usually between mates, and usually with highly-coordinated sounds) and use facial expressions, gestures, and body postures to communicate. Tactile behavior involves grooming, mating, play and sometimes aggression. [Sources: Wikipedia, Jennifer Kuester, Animal Diversity Web (ADW) /=]

agile gibbon range

The average group size for Agile gibbons is four individuals. The group usually consists of the male and female mated pair, an infant, and a juvenile. According to Animal Diversity Web: When an individual agile gibbon disperses from its natal group (when it has reached sexual maturity), it finds a mate that it will spend the rest of its life with. These monogamous bonds are important for raising young and for defending the pair's territory. Agile gibbons defend a territory by "singing". In the early morning, great calls can be heard throughout the upper canopy. These singing bouts are often duets (joint displays, usually between mates, and usually with highly-coordinated sounds) and are a way of claiming home territory. When singing is not enough to keep intruders away, both male and female gibbons will chase the intruder away. /=\

Agile gibbons are monogamous (have one mate at a time) and stay together until one of them dies. They engage in year-round breeding. The interbirth period is are around 3.3 years. The average number of offspring is one. The average gestation period is seven months. Most female gibbons nurse and care for their offspring until the offspring are about two years old. Offspring remain with their parents until they reach sexual maturity, around eight years, they then disperse from their natal group. Males also particpate in parental care in this monogamous species. Males groom offspring, and help to defend them. A mated pair can produce five to six offspring during their reproductive lifetime.

Kloss's Gibbons

Kloss’s gibbons (Hylobates klossi) live in Siberut, Sipura, North Pagai, and South Pagai in the Mentawai Islands off of western Sumatra in Indonesia. They prefer the the upper canopy of semi deciduous monsoon forests and tropical evergreen forests and estimated to have a lifespan in the wild of up to 25 years. The gibbons are named after the English ethnologist and zoologist, Cecil Boden Kloss (1877–1949), who also has several reptiles and a mole that bear his name. [Source: Alix Marcoux, Animal Diversity Web (ADW) /=]

Kloss’s gibbons have long forearms for brachiation (swinging from tree limb to tree limb using their arms) and dense, glossy, black hair with buttock pads and a large throat sac located under the chin. The throat sac helps to enhance their calls. Females are slightly larger than males, These gibbons have a head and body length that ranges from 44 to 63.5 centimeters (17.32 to 25.00 inches) and have an average weight is 5.7 kilograms (12.56 pounds). Sexual Dimorphism (differences between males and females) is present: Females are slightly larger than males, with males weighing about 5.6 kilograms and females weighing about 5.9 kilograms.

Kloss' gibbons are primarily frugivorous (fruit eating) but they have been observed eating flowers, birds, mammals, amphibians, reptiles, eggs and insects. They prefer to eat fruits with high sugar content, such as figs, which they consumer 72 percent of the time. They consume flowers, eggs, small vertebrates, and insects 25 percent of the time and have been observed to spending large amount of searching for insects. These gibbon tend to separate themselves from members of their own group — up to 50 meters away — while feeding. Natural predators include leopards, snakes, and large birds of prey. Individuals are on the alert for danger and will warn other members if a threat is perceived.

It has been estimated that there are are around 20,000 to 25,000 Kloss's gibbons in the wild, but their numbers are declining. On the International Union for Conservation of Nature (IUCN) Red List they are listed 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 main threats are loss of quality of habitat, an increased human population, hunting, and deforestation.

Kloss's Gibbon Behavior and Reproduction

Kloss's gibbon

Kloss’s gibbons 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), territorial (defend an area within the home range) and social (associates with others of its species; forms social groups). Mated pairs of males and females, with their young, form the basic social unit. The average territory size for a mated pair and their family group is 20 to 35 hectares (50 to 86 acres) of which 10 hectares is defenders from up to six other groups that occupy the surrounding square kilometer. [Source: Alix Marcoux, Animal Diversity Web (ADW) /=]

Kloss’s gibbons move through trees using brachiation (swinging from tree limb to tree limb using their arms). Often these trees are at least 10 meters apart and they move move through the air not supported by any trees, almost as if they are flying. On the ground, they can move bipedally for very short distances. They move an average of 1,514 meters per day and often sleep in the same tree at night. They are active up to 10 hours per day. Adolescents and sub-adult males join father to protect the group's territory.

Kloss’s gibbons are monogamous (have one mate at a time). The testicular sac in males is covered by short, sparse hairs. In females, the labia majora is prominent, making it difficult to distinguish males from females. These gibbon engage in year-round breeding. One infant is born every two to three years to an individual female, with the average number of offspring being one. The gestation period lasts seven to eight months. Males and females participate in caring for the young. Weaning occurs early in the second year of life. Kloss' gibbons reach sexual maturity at six to seven years of age. Young do not usually disperse from their family unit until they reach late adolescence. Often parents will assist dispersing adolescents in obtaining territory by accompanying the young into new territory and threatening rivals.

Kloss's Gibbons Unique and Beautiful Calls

Like other gibbon Kloss’s gibbon sense and communicate with vision, touch, sound and chemicals usually detected by smelling. 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). [Source: Alix Marcoux, Animal Diversity Web (ADW) /=]

What sets Kloss' gibbons apart are their beautiful and resounding vocal communication. Alix Marcoux wrote in Animal Diversity Web: Females tend to have the most distinctive calls with a slow rise and fall, interrupted by a trill sequence. Male calls consist of moans and "quiver-hoots". Males will sing solos from 10 minutes up to two hours in both the pre- and post-dawn hours. Often, breeding pairs form duets (joint displays, usually between mates, and usually with highly-coordinated sounds) together two to three hours after dawn, with the female's contribution lasting about 15 minutes.

Occasionally, the young will join in the duet of their parents. It has been hypothesized that the duets (joint displays, usually between mates, and usually with highly-coordinated sounds) are a means of intimidating neighbors to defend their territory and/or as a way to maintain social organization. Studies have shown that both males and females can be identified by the individuality of their calls, with each animal having its own unique voice./=\

Borneo Gibbons

Borneo gibbons (Hylobates muelleri) are also known as gray gibbons, southern grey gibbons, Müller's Bornean gibbons and Müller's gibbons. They live in tropical evergreen and semi-evergreen rain forests in Borneo. Formerly, the western grey gibbon (H. abbotti) and eastern grey gibbon (H. funereus) were considered conspecific with Müller's gibbons (H. muelleri), but more recent studies indicate that all three are distinct species. Borneo gibbons are are found throughout Borneo excluding the southwest region. Müller's gibbons live primarily in southeast Borneo in Kalimantan in Indonesia. They are primarily frugivores (fruit eating). The majority of the diet consists of ripe, sugar-rich, fruit and figs. A smaller portion of the diet is made up of leaves. [Source: Sandra Bruening, Animal Diversity Web (ADW) /=]

Borneo gibbon

Borneo gibbons range in weight from four to eight kilograms (8.8 to 17.6 pounds) and have a head and body length that ranges from 44 to 63 centimeters (17.3 to 25 inches). Their coloration varies from gray to brown. The top of the head and the chest are darker than the rest of the body. These gibbons have buttock pads, long canine teeth, and no tail. The basal part of the thumb extends from the wrist rather than the palm of the hand, allowing an extended range of movement. Sexual Dimorphism (differences between males and females) is not pronounced in Borneo gibbons. Both sexes are roughly equal in size and look similar. Unlike most gibbon species, Müller's gibbons do not show sexual dimorphism in their fur coloration.

On the International Union for Conservation of Nature (IUCN) Red List Borneo gibbons are listed 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. Borneo gibbons are mainly the threatened species by loss of habitat due to deforestation, logging, small scale farming and palm oil agriculture. Vast amounts of rainforest in Borneo have been lost. Borneo gibbons

Borneo Gibbon Behavior, Communication and Reproduction

Borneo gibbons 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), solitary, territorial (defend an area within the home range) and social (associates with others of its species; forms social groups). They are also very territorial (defend an area within the home range). Home ranges average 34.2 hectares in size. About 75 percent of it is defended. Defense involves regular morning songs and calling at and chasing intruders. Borneo gibbons rarely resort to physical violence when defending territory. Borneo gibbons are active for eight to 10 hours per day. They rise at dawn and settle in for the night before sunset. Males tend to become active earlier and for longer periods than females. Borneo gibbons spend most of their day foraging in the main canopy of the forest. [Source: Sandra Bruening, Animal Diversity Web (ADW) /=]

Borneo gibbons are very agile in the trees. According to Animal Diversity Web: They move quickly with long leaps and swings. They are able to cover three meters in a single swing and around 850 meters per day. Borneo gibbons walk upright with hands over head for balance when walking on the ground, although they do not cover long distances in this fashion. Borneo gibbons are not good swimmers and avoid open water. Borneo gibbons are usually seen in groups of three or four. Solitary individuals are also common. These individuals are adults who have been forced to leave the family and have not yet established their own territory.

Borneo gibbons are social creatures but do not spend as much time in social interaction as do some other primate species. Grooming and social play take up less than five percent of the daily activities. The lack of interaction may be due to the small number of social partners available. Male and female adults are, more or less, social equals. In one study, males were found to groom females more often and play with young more frequently. Too few studies have been conducted to determine if this behavior is common to all groups of Borneo gibbons. /=\

Borneo gibbons 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. Research has shown that Borneo gibbons are able to identify other species of gibbons through song. Grooming and social play are two forms of tactile communication used in this species. Like other primates, these gibbons likely use gestures, facial expressions, and body postures to communicate. /=\

The call of Borneo gibbons have been studied in detail. Adult males sing long songs before sunrise. Females sing with males after sunrise and before 10:00 AM. Their duets (joint displays, usually between mates, and usually with highly-coordinated sounds) average 15 minutes and occur on a daily basis. /=\ Lone males sing longer songs than paired males, possibly to attract mates. Unpaired females rarely sing. /=\

Borneo gibbons are monogamous (have one mate at a time), with a mated pair and their offspring forming the main social group and occupying and defendeding home range. They breed throughout the year and most often produce a single offspring every two to three years. The age of sexual maturation is eight to nine years. Females have an estrous cycle of about 28 days. There are no visible sexual swellings, although the genitalia undergo color and turgidity changes that are thought to be associated with ovulation. Males initiate mating more frequently than females. If the female is willing to mate, she bends forward in acceptance. If the female is unwilling, she ignores the male or leaves the area.

The average gestation period is seven months. The age in which they are weaned ranges from up to 24 months and the age in which they become independent ranges up to nine years. Females and males reach sexual or reproductive maturity at eight to nine years. Because young typically stay with their parents until they reach maturity, it is difficult to say from what age they might be independent.

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