The Bornean orangutan (Pongo pygmaeus) is an orangutan species endemic to the island of Borneo. It belongs to the only genus of great apes native to Asia and is the largest of the three Pongo species. It has a coarse, reddish coat and up to long arms. It is sexually dimorphic — males are larger than females and develop large cheek pads (flanges).
The Bornean orangutan inhabits Borneo lowland rain forests and Borneo montane rain forests up to an elevation of . Its diet includes fruits, seeds, flowers, bird eggs, sap and vines. It is highly intelligent, displaying tool use and distinct cultural patterns. It is listed as Critically Endangered, with deforestation, palm oil plantations, and hunting posing a serious threat to its survival. It is scheduled as a "totally protected animal" under Sarawak state law through the 1998 Wild Life Protection Ordinance.
Taxonomy
The Bornean orangutan was originally named and scientifically described by Carl Linnaeus in 1799 under the scientific name Simia satyrus, meaning "satyr monkey", but was changed when scientists discovered that not all orangutans are one species. The holotype of this organism is located in the British Museum in London. It has three subspecies: Northwest Bornean orangutan Pongo pygmaeus pygmaeus – Sarawak and northern West Kalimantan; Central Bornean orangutan P. p. wurmbii – Southern West Kalimantan and Central Kalimantan; Northeast Bornean orangutan P. p. morio – East Kalimantan and Sabah.
There is some uncertainty about this, however. The population currently listed as P. p. wurmbii may be closer to the Sumatran orangutan (P. abelii) than to the Bornean orangutan. If this is confirmed, P. abelii would be a subspecies of P. wurmbii (Tiedeman, 1808). In addition, the type locality of P. pygmaeus has not been established beyond doubt; it may be from the population currently listed as P. wurmbii (in which case P. wurmbii would be a junior synonym of P. pygmaeus, while one of the names currently considered a junior synonym of P. pygmaeus would take precedence for the taxon in Sarawak and northern West Kalimantan). Bradon-Jones et al. considered P. morio to be a synonym of P. pygmaeus, and the population found in East Kalimantan and Sabah to be a potentially unnamed separate taxon.
Etymology The genus name Pongo is derived from the Bantu word used to indicate a large primate. It was originally used to describe chimpanzees in Western African dialects. The species name pygmaeus is derived from the Greek word "pygmy" meaning dwarf.
Evolution
Bornean orangutans diverged from Tapanuli orangutans about 674,000 years ago. The Bornean orangutan and the Sumatran orangutan diverged about 400,000 years ago, with a continued low level of gene flow between them since then. The Bornean orangutan and the Sumatran orangutan were considered merely subspecies until 1996; they were elevated to species following sequencing of their mitochondrial DNA. Tapanuli orangutan was identified as a distinct species in 2017.
The first complete orangutan fossil skeleton was discovered in the Hòa Bình Province in Vietnam and thought to be from the late Pleistocene epoch. It differed from modern orangutans only in that its body was proportionately smaller compared to its head. This fossil and others confirm that orangutans once inhabited continental Southeast Asia.
Description
The Bornean orangutan is the third-largest ape after the western gorilla, and the largest truly arboreal (or tree-dwelling) extant ape.EDGE :: Mammal Species Information . Edgeofexistence.org. Retrieved on 2012-08-21. Body weights broadly overlap with the considerably taller Homo sapiens, but the latter is considerably more variable in size.Novak, R. M. 1999. Walker's Mammals of the World. 6th edition. Johns Hopkins University Press, Baltimore. By comparison, the Sumatran orangutan is similar in size but, on average, is marginally lighter in weight.WWF – Sumatran Orangutan – Close relative in dire straits. Worldwildlife.org. Retrieved on 2012-08-21.The Bornean and Sumatran Orangutans | Visuallens. Visuallens.wordpress.com (2008-08-02). Retrieved on 2012-08-21. A survey of wild orangutans found that males weigh on average , ranging from , and long; females average , ranging from , and long. While in captivity, orangutans can grow considerably overweight, up to more than .Giza Zoo > Bornean Orangutan إنسان الغابة. Gizazoo-eg.com. Retrieved on 2012-08-21. The heaviest known male orangutan in captivity was an obese male named "Andy", who weighed in 1959 when he was 13 years old.
The Bornean orangutan has a distinctive body shape with very long arms that may reach up to 1.5 metres in length. It has grey skin, a coarse, shaggy, reddish coat and prehensile, grasping hands and feet. Its coat does not cover its face unlike most mammals, although Bornean orangutans do have some hair on their faces including a beard and mustache. It also has large, fatty cheek pads known as flanges as well as a pendulous throat sac.
Bornean orangutans are highly sexually dimorphic and have several features that differ between males and females. Males have much larger cheek pads, or flanges, that are composed of muscle and large amounts of fat. In females, the flanges are mostly composed of muscle. Males have relatively larger canines and premolars. Males have a more pronounced beard and mustache. The throat sac in males is also considerably larger. There are two body types for sexually mature males: smaller or larger. Larger males are more dominant but smaller males still breed successfully. There is little sexual dimorphism at birth.
Distribution and habitat The Bornean orangutan occurs in the two Malaysian states of Sabah and Sarawak, and four of the five Indonesian Provinces of Kalimantan, while its presence in Brunei is uncertain and unconfirmed; due to habitat destruction, its distribution is patchy throughout the island, and it has become rare in the southeast of Borneo and in the forest between the Rajang River in central Sarawak and the Padas River in western Sabah It lives in the Borneo lowland rain forests and in the Borneo montane rain forests in mountainous areas up to . It inhabits the canopy of old-growth and secondary forests, and moves large distances to find fruit-bearing trees.
In early October 2014, researchers found about 50 orangutans in several groups in South Kalimantan Province, although previously there is no record that the province has orangutans.
Behavior and ecology
In history, orangutans ranged throughout Southeast Asia and into southern China, as well as on the island of Java and in southern Sumatra. They primarily inhabit peat swamp forest, tropical heath forest, and mixed dipterocarp forest. Bornean orangutan are more solitary than their Sumatran relatives. Two or three orangutans with overlapping territories may interact, but only for short periods of time. Although orangutans are not territorial, adult males will display threatening behaviors upon meeting other males, and only socialize with females to mate. Males are considered the most solitary of the orangutans. The Bornean orangutan has a lifespan of 35–45 years in the wild; in captivity it can live to be about 60.
Despite being arboreal, the Bornean orangutan travels on the ground more than its Sumatran counterpart. This may be in part because no large terrestrial predators could threaten an orangutan in Borneo. In Sumatra, orangutans must face predation by the fierce Sumatran tiger.
The Bornean orangutan exhibits nest-building behavior. Nests are built for use at night or during the day. Young orangutans learn by observing their mother's nest-building behaviour. This skill is practiced by juvenile orangutans. Nests may be elaborate and involve a foundation and mattress made by intertwining leaves and branches and adding broken leafy branches. Additional features such as shade, waterproof roof, "pillow", and "blanket", all of which are made from branches, twigs and leaves, may also be added. Nest-building in primates is considered as an example of tool use and not animal architecture.
The species has been observed using tools such as leaves to wipe off faeces, a pad of leaves for holding spiny durian fruit, a leafy branch for a bee swatter, a bunch of leafy branches held together as an "umbrella" while traveling in the rain, a single stick as backscratcher, and a branch or tree trunk as a missile.
Diet
The Bornean orangutan's diet is composed of over 400 types of food, including wild figs, Durio zibethinus and D. graveolens, leaves, seeds, flowers, sap, the inner shoots of plants and vines, bark, honey, fungi, bird eggs, spider webs and insects. It get the necessary quantities of water from both fruit and from tree holes. Some individuals have been observed eating dead fish on shores and even grabbing live fish out of the water. In some regions, it occasionally eats soil to get minerals that may neutralize toxins and acids consumed in the vegetarian diet. On rare occasions, it preys upon smaller primates, such as slow lorises.
Dental microwear texture analysis suggests no significant dietary variation exists between Bornean orangutans of different sexes or ages.
Reproduction
Males and females generally come together only to mate. Subadult males try to mate with any female and are successful around half the time. Dominant flanged males will call and advertise their position to receptive females, who prefer mating with flanged males. Adult males will often target females with weaned infants as mating partners because the female is likely to be fertile.
Females reach sexual maturity and experience their first ovulatory cycle between about six and 11 years of age, although females with more body fat may experience this at an earlier age. The estrous cycle lasts between 22 and 30 days and menopause has been reported in captive orangutans at about age 48. Females tend to give birth at about 14–15 years of age. Newborn orangutans nurse every three to four hours, and begin to take soft food from their mothers' lips by four months. During the first year of its life, the young clings to its mother's abdomen by entwining its fingers in and gripping her hair. Offspring are weaned at about four years, but this could be much longer, and soon after they start their adolescent stage of exploring, but always within sight of their mother. During this period, they will also actively seek other young orangutans to play with and travel with. On average, juveniles do not become completely independent until they are about seven years of age. The birth rate for orangutans has been decreasing largely due to a lack of sufficient nutrients as a result of habitat loss.
A 2011 study on female orangutans in free-ranging rehabilitation programs found that individuals that were supplemented with food resources had shorter interbirth intervals, as well as a reduced age, at first birth.
Conservation status The Bornean orangutan is more common than the Sumatran, with about 104,700 individuals in the wild, whereas just under 14,000 Sumatran orangutans are left in the wild. Orangutans are becoming increasingly endangered due to habitat destruction and the bushmeat trade, and young orangutans are captured to be sold as pets, usually entailing the killing of their mothers.