Geographic Distribution and Habitat
White-handed gibbons, also known as lar gibbons, live in the tropical rainforests of southern and Southeast Asia. Of all the gibbon species, white-handed gibbons inhabit the greatest north-south range. They make their homes in the countries of Indonesia, Laos, Malaysia, Myanmar, and Thailand.
Scientists speculate on the existence of five subspecies of white-handed gibbon: Malaysian lar gibbon (Hylobates lar lar), found in the Malaysia peninsular and possibly Thailand; Carpenter’s lar gibbon, (H. l. carpenteri), found in Myanmar, west Laos, and north Thailand; Central lar gibbon (H. l. entelloides), found in southeast Myanmar and in central and south Thailand; Sumatran lar gibbon (H. l. vestitus), found over the northern third of the island of Sumatra; and the Yunnan lar gibbon (H. l. yunnanensis), once found in Southwest Yunnan, China. Most scientists believe that the Yunnan lar gibbon is now extinct.
Of all the white-handed gibbon subspecies, only the Sumatran lar gibbon is geographically separated from the others; however, its genetic makeup and environmental influences (physical adaptions, for example) are not greatly distinct from other white-handed gibbon subspecies. In fact, none of these subspecies is especially distinct from one another. With individual classification based mostly on slight color variations in their coats, scientists call for more thorough investigation into the validity of each subspecies.
Preferred habitats of white-handed gibbons include dipterocarp forests, submontane forests, lowland forests, seasonal evergreen forests, peat swamp forests, bamboo forests, mixed deciduous forests, and semi-deciduous monsoon forests. Their home territories range from 42 to 99 acres (17 to 40 hectares)
An arboreal species, white-handed gibbons live in the upper tree canopy, at an altitude of up to 3,937 ft (1,200 m) above sea level. Rarely are these lesser apes found in the understory, and are thought never to descend to the forest floor.
Size, Weight, and Lifespan
Male white-handed gibbons are slightly larger than females.
Head-to-body length in males ranges from 17 to 23 in (43.5 to 58.5 cm), and they weigh between 11 and 16.8 lb (5 to 7.6 kg).
Head-to-body length in females ranges from 16.5 to 22.8 in (42 to 58 cm), and they weigh between 9.7 to 15 lb (4.4 to 6.8 kg).
The average lifespan for wild white-handed gibbons is 30 years. Captive white-handed gibbons live 44 years, on average.
Individuals are cloaked in soft, dense hair (known as pelage) that is either light or dark in overall color, with light individuals having buff or creamy hair, and dark individuals having brown or black hair. Nuances in color occur in both light- and dark-colored coats. The hairless, black faces of white-handed gibbons are adorned with short white fringe that adds a bit of “primate pizzazz” to their beguiling appearance. They assess the world through expressive, dark eyes. As their name indicates, the hair that covers the hands of white-handed gibbons is white, and their feet are covered with white hair, too.
Genetics determines whether a white-handed gibbon wears a light- or dark-colored coat. If both parents have light hair, then their offspring will have light hair; conversely, if both parents have dark hair, their offspring will have dark hair. Hair color has no bearing on mating, however. If one of the parents has a dark coat and the other parent has a light coat, the dominant gene is passed to their baby; that is, their baby receives the inheritance of a dark-colored coat.
Three of the four suggested viable subspecies are also either light- or dark-colored, with nuances in color.
Malaysian lar gibbons are medium brown or dark chocolate brown in the dark form (overall color) with a lighter torso and darker legs. In the light form (overall color), they are a creamy color.
Carpenter’s lar gibbons are long-haired and almost black or brownish charcoal in the dark form. In the light form, they are creamy white or white-buff.
Central lar gibbons are black or black-brown in the dark form. In the light form, they are honey-colored with darker legs.
Sumatran lar gibbons are always light with no dark form and are typically light brown, with a buff back, pale lower back, and a brown head, abdomen, and limbs.
As lesser apes, gibbons are distinguished from great apes (chimpanzees, bonobos, gorillas, orangutans and humans) for their smaller size, low sexual dimorphism, and a superficial resemblance to monkeys.
Like all apes, white-handed gibbons have no tail, but they are fitted with small areas of hardened, leathery skin (known as ischial callosities) on their rump. These “seat pads” allow the primates to sit securely on thin branches, even allowing them to sleep while sitting upright, without the risk of falling.
Nature has equipped white-handed gibbons with super-long arms that allow them to swing from tree branch to tree branch, alternately supporting their body under each forelimb, an acrobatic feat known as brachiation. Or, they might simply hang from a branch with their arms fully extended.
White-handed gibbons are mostly frugivorous—that is, they eat a lot fruit. They especially love figs, which can make up to half their diet. Fruit from the liana vine (a long-stemmed woody vine that twines itself around other plants and is common in tropical rainforests), other sweet fruits, and berries are also enjoyed. Leafy plants, flowers, young leaves, new shoots, insects, and occasional birds’ eggs are on the white-handed gibbons’ menu, too.
Diet varies with the seasons. In Thailand, for example, flowers are prevalent in the cool season, while ripe fruit is abundant during the hot, wet seasons. The months of November and December yield the figs that white-handed gibbons most enjoy.
When it comes to fruit consumption, white-handed gibbons exhibit a discriminating palate. To find the ripest fruit, they taste-test several pieces. Those pieces deemed unripe are rejected. During peak season, white-handed gibbons revisit the same fruit trees multiple times.
White-handed gibbons may share their food with one another. However, this behavior might be less of an unselfish act and more an act of appeasement; scientists have observed individuals begging other individuals for food.
To drink water, white-handed gibbons cup their hands and scoop water that has collected in tree holes.
Competitors for food sources include pigtail macaques (Macaca nemestrina) whom scientists have observed foraging and interacting with white-handed gibbons; long-tailed macaques (Macaca fascicularis); dusky leaf monkeys (Trachypithecus obscurus); and siamangs (Symphalangus syndactylus), the largest of the gibbons whose distribution overlaps that of white-handed gibbons.
Behavior and Lifestyle
White-handed gibbons are diurnal creatures, meaning that they are active during daylight hours. An adult male sounds reveille each dawn, emitting a solo call that tells the others in his family that it’s time to get up. The group wakens, takes care of their “bathroom business” while hanging from a tree branch, and begins to forage through their treed habitat.
Gibbons are masters of agility and white-handed gibbons are no exception. Although these primates lack a tail, they possess an innate sense of balance. They have been observed, high above the forest floor, walking across branches bipedally (that is, on their hind legs) with their arms raised above their head to help steady their step (think of a tightrope walker!).
Fitted with ball-and-socket wrist joints, these long-armed supreme brachiators move fluidly and effortlessly, swinging up to nearly 50 ft (15 m) at up to 35 mph (56 kmh); they can leap an impressive 26 ft (8 m) between branches.
But even the rainforest’s most graceful trapeze artists sometimes fall—whether the cause is a hand that loses its grip on a branch, or a branch that snaps. Scientists speculate that most gibbons suffer one or more bone fractures during their lifetimes.
White-handed gibbons retire to their sleeping trees several hours before dusk. Unlike great apes, these lesser apes do not make nests. Individuals sleep one to a tree, neighboring one another. By selecting the tallest trees to spend the night, their movements between trees are less easily observed by potential predators. These highly vocal primates are uncharacteristically quiet when in their sleeping trees, again to avoid attracting the attention of potential predators, who include cloud leopards, tigers, pythons, hawks, and eagles. If threatened, white-handed gibbons might mob together to chase off a predator.
Hylobates (the genus that includes the white-handed gibbon) means “forest walker” in the Greek language, from the Greek hūlē (“forest”) and bates (“one who treads”).
The Chinese word yuán once referred to China’s gibbon population, specifically, the Yunnan lar gibbon, now presumed extinct due to habitat destruction throughout the country. In modern usage, yuán is a generic word for ape.
Early Chinese writers regarded gibbons as “noble gentlemen” who moved gracefully, high through the treetops.
Early followers of Taoism once ascribed occult properties to gibbons, believing them capable of living for several hundred years possessing the ability to turn into humans.
Gibbon figurines dating back to the fourth to third centuries BCE (the Zhou dynasty) have been found in China. Later, gibbons became a popular subject for Chinese painters.
Gibbons solely occupy the lesser ape category. But they have plenty of gibbon company. In addition to the genus Hylobates, there are three other genera of gibbons, each containing multiple species: Hoolock; Nomascus; and Symphalangus, the genus to which the siamang gibbon (the sometimes food competitor of the white-handed gibbon) belongs.
White-handed gibbons may be lesser apes, but they are no less impressive than other primates. Gibbons’ supreme agility and masterful swinging through the rainforest distinguish them from their great ape cousins.
White-handed gibbons live in social family groups of two to six members, typically consisting of a mated pair and their offspring. The species is mostly monogamous, with an adult breeding couple usually forming lifelong bonds.
When it comes to foraging expeditions, adult males typically lead; however, depending on location, an adult female might lead the group in its search for food. Home range for different white-handed gibbon groups may overlap, and a group will defend its territory during intergroup encounters.
The entire group takes an hour-long rest and recreation break in between foraging and feeding activities. Individuals spend part of this time grooming one another, an activity that strengthens social bonds and is known as allogrooming. Some scientists place more emphasis on the hygienic role that allogrooming serves, with these primates helping one another to stay clean and free of parasites.
White-handed gibbons communicate through song, rich vibratos that reverberate through their rainforest habitat. In addition to an adult male’s morning wake-up reveille, elaborate duets are part of the species’ musical repertoire.
An adult bonded pair sings a duet before noontime each day. Their loud and distinctive song, enhanced by a sound-amplifying throat sac, lasts an average of 11 minutes and can be heard up to 0.6 mi (1 km) away.
Their duet begins with an introductory call, consisting of a series of notes by the male and the female; followed by a “great call,” notes initiated by the female and answered by the male; and ends with an interlude sequence, with both the male and female sounding musical notes and the male giving his answering call. Scientists speculate that this duet helps to maintain bonds between the breeding pair and also serves to define the boundaries of their territory.
To defend a group’s territory, adult males will position themselves at the boundaries and sing a song together—a song that tells outsiders to keep away.
Through song, the species of gibbon and the area from which it comes can be identified.
Although monogamy is the social norm with females who live in smaller home ranges with dense resources, polyandry is sometimes practiced by females who live in larger home ranges with fewer natural resources.
Female white-handed gibbons reach sexual maturity between 6 and 9 years old; males reach sexual maturity at 9 years old. These primates breed year-round.
After a 7-month gestation period, a female gives birth to a single offspring. She reproduces every 3.5 years. Mothers are the primary caregivers to their infants; however, dads and elder siblings might pitch in. Infants are considered weaned at age 20 months. Gibbons have one of the longest juvenile periods among nonhuman primates, approximately 7 years. Offspring remain with their parents until they reach sexual maturity.
Thanks to their frugivorous diet, white-handed gibbons are capable forest cultivators. They help to stimulate plant growth and replenish their habitat through the seeds they disperse through their feces.
White-handed gibbons are classified as Endangered by the International Union for Conservation of Nature, appearing on the Red List of Threatened Species (IUCN, 2015).
The major threat to white-handed gibbons is hunting—having replaced forest clearance as the primary threat. They are hunted both for food and for the pet trade. Hunting pressure varies across the range but takes place even within protected areas.
Construction of roads through protected areas poses additional threats since it promotes forest clearance and strip development, increases fragmentation, and increases access by hunters into protected areas. Ongoing localized forest loss due to shifting agriculture and commercial plantations of palm oil also poses a threat.
White-handed gibbons are listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. However, as is often the case with endangered species, laws created to protect them are largely ignored and difficult to enforce.
Those white-handed gibbons who reside within the boundaries of national parks and reserves are, in theory, afforded some protections. Unfortunately, these protected areas are often poorly supervised and laws against their capture are routinely flouted. Furthermore, ongoing agricultural development through these areas increases fragmentation of white-handed gibbon populations and leaves them more vulnerable to hunters, who now have easier access to these endangered primates.
Conservationists warn that unless the highest priority is given to protecting white-handed gibbon habitat, the species will become Critically Endangered, only a step away from extinction.
- http://eol.org/pages/1652/overview http://www.slate.com/articles/health_and_science/science/2008/07/the_forgotten_ape/
Written by Kathleen Downey, December 2017. Conservation status updated July 2020