The lar gibbon (Hylobates lar), also known as the white-handed gibbon, is an endangered primate in the gibbon family, Hylobatidae. It is one of the better-known gibbons and is often kept in captivity.

Taxonomy

There are five subspecies of lar gibbon:

  • Malaysian lar gibbon (H. l. lar)
  • Carpenter's lar gibbon (H. l. carpenteri)
  • Central lar gibbon (H. l. entelloides)
  • Sumatran lar gibbon (H. l. vestitus)
  • Yunnan lar gibbon (H. l. yunnanensis) (possibly extinct)<!-- http://www.mediadesk.uzh.ch/mitteilung.php?text_id=294&grp=aktuell -->

Physical description

thumb|left|A close-up of head

The fur coloring of the lar gibbon varies from black and dark-brown to light-brown, sandy colors. The hands and feet are white-colored, likewise a ring of white hair surrounds the black face. Both males and females can be all color variants, and the sexes also hardly differ in size. Gibbons are true brachiators, propelling themselves through the forest by swinging under the branches using their arms. Reflecting this mode of locomotion, the white-handed gibbon has curved fingers, elongated hands, extremely long arms and relatively short legs, giving it an intermembral index of 129.7, one of the highest of the primates. As with all apes, the number of caudal vertebrae has been reduced drastically, resulting in the loss of a functional tail. Gibbons have tough, bony padding on their buttocks, known as the ischial callosities, or sitting pads.

Distribution and habitat

thumb|right|220px|Climbing lar gibbon showing the darker fur of some individualsthumb|Mother & Infant in [[Singapore Zoo]]

Lar gibbons have the greatest north-south range of any of the gibbon species. They are found in Indonesia, Laos, Malaysia, Myanmar and Thailand. Their range historically extended from southwest China to Thailand and Burma south to the whole Malay Peninsula in primary and secondary tropical rain forests. It is also present in the northwest portion of the island of Sumatra. In recent decades, especially, the continental range has been reduced and fragmented. Lar gibbons are likely extinct in China. However, if any populations persist, they would only be found in southwest Yunnan, their former range.

The gibbon genus is highly allopatric, usually separated by large rivers. As a result, their range extends through southern and eastern Myanmar, but only east of the Salween River. They are found through the Malay Peninsula. Lar gibbons also exist west of the Mekong River in northwestern Laos and northern Sumatra.

The lar gibbon can be found living in sympatry with several other primates and apes, including orangutans (Pongo pygmaeus), siamangs (S. syndactylus), pileated gibbons (Hylobates pileatus), purple-faced langurs (Semnopithecus spp.), Thomas's langur (Presbytis thomasi), slow loris (Nycticebus coucang), and several macaques (Macaca spp.)

In Thailand, lar gibbons probably number between 15,000 and 20,000, though there may be as few as 10 in China, if any.

Diet and dentition

thumb|right|A lar gibbon eating carrots

The lar gibbon is considered frugivorous with fruit constituting 50% of its diet, but leaves (29%) are a substantial part, with insects (13%) and flowers (9%) forming the remainder. During the summer months, when figs and leaves are less available, insect consumption increases twenty-fold relative to the winter. They rarely come to the ground, instead using their long arms to brachiate through the trees. With their hooked hands, they can move swiftly with great momentum, swinging from the branches. Although they rarely come to the ground naturally, while there, they walk bipedally with arms raised above their heads for balance.

Their social organization has been characterized as monogamous family pairs, with one breeding male and one female along with their juvenile offspring. However, this traditional conception has come under scrutiny. Long-term studies conducted in Khao Yai National Park in Thailand suggest their mating system is somewhat flexible, incorporating extra-pair copulations, partner changes and polyandrous groupings. This multimale polyandry may be attributed to cooperative territory use and female defense. As range size increases, males are more successful in defending it in a pair or group. Additionally, these extra pair copulations may increase the chance of reproduction with a mate of superior genetic quality and decrease the chance of infanticide.

Vocalisations

thumb|right|180px|Pair of lar gibbons hooting

Family groups inhabit a firm territory, which they protect by warding off other gibbons with their calls. Each morning, the family gathers on the edge of its territory and begins a "great call", a duet between the breeding pair. Each species has a typified call and each breeding pair has unique variations on that theme. The great call of Hylobates lar is characterized by its frequent use of short hoots with more complex hoots, along with a "quavering" opening and closing. These calls are one of the traits used determining species differences among the gibbons.

Reproduction

Sexually, they are similar to other gibbons. Mating occurs in every month of the year, but most conceptions occur during the dry season in March, with a peak in births during the late rainy season, in October. On average, females reproduce for the first time at about 11 years of age in the wild, much later than in captivity. Gestation is six months long on average, and pregnancies are usually of a single young. Young are nursed for approximately two years, and full maturity comes at about eight years. The life expectancy of the lar gibbons in the wild is about 25 years.

Conservation

thumb|right|alt=Video showing a lar gibbon monkey holding on to cage bars|A captive lar gibbon looks out from its cage.

Lar gibbons are threatened in various ways: they are sometimes hunted for their meat, sometimes a parent is killed to capture young animals for pets, but perhaps the most pervasive is the loss of habitat. Lar gibbon habitats are already threatened by forest clearance for the construction of roads, agriculture, ecotourism, domesticated cattle and elephants, forest fires, subsistence logging, illegal logging, new village settlement, and palm oil plantations.

Predation

Potential predators of lar gibbons in the Sikundur Monitoring Post include Sumatran tigers, Sunda clouded leopards, pythons (Python spp.) and grey-headed fish eagles.

References

  • ARKive - images and movies of the white-handed gibbon (Hylobates lar)
  • Lar Gibbon photos
  • Lar Gibbon songs
  • Gibbon Conservation Center
  • Lar Gibbon at Animal Diversity Web
  • Thomas Geissmann's Gibbon Research Lab and Gibbon Network