Orangutan

The orangutans (also spelled orang-utan, orangutang, or orang-utang) are three extant species of great apes native to Indonesia and Malaysia. Orangutans are currently found in the rainforest of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus Pongo, orangutans were originally considered to be one species. From 1996, they were divided into two species: the Bornean orangutan (P. pygmaeus, with three subspecies) and the Sumatran orangutan (P. abelii). In November 2017, it was reported that a third species had been identified: the Tapanuli orangutan (P. tapanuliensis). The orangutans are the only surviving species of the subfamily Ponginae, which also included several other species, including the largest known primate, Gigantopithecus blacki. The ancestors of the Ponginae split from the main ape line in Africa 15.7 to 19.3 million years ago (mya).

Orangutans
Temporal range: Early Pleistocene–Recent
Orang Utan, Semenggok Forest Reserve, Sarawak, Borneo, Malaysia.JPG
Bornean orangutan
(Pongo pygmaeus)
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Hominidae
Subfamily: Ponginae
Genus: Pongo
Lacépède, 1799
Type species
Pongo borneo
Lacépède, 1799 (Simia satyrus Linnaeus, 1760)
Species

Pongo pygmaeus
Pongo abelii
Pongo tapanuliensis
Pongo hooijeri

Orangutan range.png
Range of the three extant species
Synonyms

Faunus Oken, 1816
Lophotus Fischer, 1813
Macrobates Billberg, 1828
Satyrus Lesson, 1840

Orangutans are the most arboreal of the great apes and spend most of their time in trees. Their hair is reddish-brown, instead of the brown or black hair typical of chimpanzees and gorillas. Flanged (the distinctive cheek pads) adult males have long calls that attract females and intimidate rivals; younger unflanged ones do not and resemble adult females. Orangutans are the most solitary of the great apes, with social bonds occurring primarily between mothers and their dependent offspring, who stay together for the first two years. Fruit is the most important component of an orangutan's diet; however, the apes will also eat vegetation, bark, honey, insects and even bird eggs. They can live over 30 years both in the wild and in captivity.

Orangutans are among the most intelligent primates; they use a variety of sophisticated tools and construct elaborate sleeping nests each night from branches and foliage. The apes have been extensively studied for their learning abilities. There may even be distinctive cultures within populations. Orangutans have been featured in literature and art since at least the 18th century, particularly in works which comment on human society. Field studies of the apes were pioneered by primatologist Birutė Galdikas and they have been kept in captive facilities around the world since at least the early 19th century. All three orangutan species are considered to be critically endangered. Human activities have caused severe declines in populations and ranges. Threats to wild orangutan populations include poaching, habitat destruction as a result of palm oil cultivation, and the illegal pet trade. Several conservation and rehabilitation organisations are dedicated to the survival of orangutans in the wild.

Etymology

The name "orangutan" (also written orang-utan, orang utan, orangutang, and ourang-outang[1]) is derived from the Malay and Indonesian words orang, meaning "man", and hutan, meaning "forest",[2] thus "man of the forest".[3]

The first attestation of the word orangutan to name the Asian ape is in Dutch physician Jacobus Bontius' 1631 Historiae naturalis et medicae Indiae orientalis – he reported that Malays had informed him the ape was able to talk, but preferred not to "lest he be compelled to labour".[4] The word appeared in several German-language descriptions of Indonesian zoology in the 17th century. The likely origin of the word comes specifically from the Banjarese variety of Malay.[5]

Cribb and colleagues (2014) suggest that Bontius' account referred not to apes (which were not known from Java) but rather to humans suffering some serious medical condition (most likely cretinism) and that his use of the word was misunderstood by Nicolaes Tulp, who was the first to use the term in a publication.[6]:14–18

The word was first attested in English in 1691 in the form orang-outang, and variants with -ng are found in many languages. This spelling (and pronunciation) has remained in use in English up to the present, but has come to be regarded as incorrect.[7][8][9] The loss of "h" in Utan and the shift from -ng to -n has been taken to suggest that the term entered English through Portuguese.[5] In 1869, the British naturalist Alfred Russel Wallace published his account of Malaysia's wildlife: The Malay Archipelago: The Land of the Orang-Utan and the Bird of Paradise.[4]

The name of the genus, Pongo, comes from a 16th-century account by Andrew Battel, an English sailor held prisoner by the Portuguese in Angola, which describes two anthropoid "monsters" named Pongo and Engeco. He is now believed to have been describing gorillas, but in the 18th century, the terms orangutan and pongo were used for all great apes. Lacépède used the term Pongo for the genus following the German botanist Friedrich von Wurmb who sent a skeleton from the Indies to Europe.[10] Battel's "Pongo", in turn, is from the Kongo word mpongi[11][12] or other cognates from the region: Lumbu pungu, Vili mpungu, or Yombi yimpungu.[13]

Taxonomy, phylogeny and genetics

The three orangutan species are the only extant members of the subfamily Ponginae. This subfamily also included the extinct genera Lufengpithecus, which lived in southern China and Thailand 2–8 mya, and Sivapithecus, which lived India and Pakistan from 12.5 mya until 8.5 mya. These apes likely lived in drier and cooler environments than orangutans do today. Khoratpithecus piriyai, which lived in Thailand 5–7 mya, is believed to have been the closest known relative of the orangutans. The largest known primate, Gigantopithecus, was also a member of Ponginae and lived in China, India and Vietnam from 5 mya to 100,000 years ago.[14]:50

Within apes (superfamily Hominoidea), the gibbons diverged during the early Miocene (between 19.7 and 24.1 mya, according to molecular evidence) and the orangutans split from the African great ape lineage between 15.7 and 19.3 mya.[15](Fig. 4)

Taxonomy of genus Pongo[16] Phylogeny of superfamily Hominoidea[15](Fig. 4)
  • Genus Pongo
    • Bornean orangutan (Pongo pygmaeus)
      • Pongo pygmaeus pygmaeus – northwest populations
      • Pongo pygmaeus morio – east populations
      • Pongo pygmaeus wurmbii – southwest populations
    • Sumatran orangutan (Pongo abelii – northwest of Lake Toba)
    • Tapanuli orangutan (Pongo tapanuliensis – in Sumatra south of Lake Toba)
 Hominoidea

humans (genus Homo)

chimpanzees (genus Pan)

gorillas (genus Gorilla)

orangutans (genus Pongo)

gibbons (family Hylobatidae)

History of orangutan taxonomy

 
Art by John Gerrard Keulemans in Handbook to the Primates, Volume II (1897)

The orangutan was first described scientifically in 1758 in the Systema Naturae of Linnaeus as Simia satyrus.[6]:20 The populations on the two islands were classified as separate species when P. abelii was described by Lesson in 1827.[17] Later P. abelii was placed under P. pygmaeus in 1985 as a subspecies.[18] In 1996, P. abelii was elevated back to full species status,[19][14]:53 and the three distinct populations on Borneo were elevated to subspecies. The population currently listed as P. p. wurmbii may be closer to the Sumatran orangutan than the other Bornean orangutan subspecies. If confirmed, abelii would be a subspecies of P. wurmbii (Tiedeman, 1808).[20]

Regardless, the type locality of P. pygmaeus has not been established beyond doubts, and 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 northwest Bornean taxon). To further confuse, the name P. morio, as well as some suggested junior synonyms, may be junior synonyms of the P. pygmaeus subspecies, thus leaving the east Bornean populations unnamed.[20]

The description in 2017 of a third species, P. tapanuliensis, from Sumatra south of Lake Toba, came with a surprising twist: it is more closely related to the Bornean species, P. pygmaeus than to its fellow Sumatran species, P. abelii.[21]

Fossil record

The oldest known record of Pongo is known from the early Pleistocene of Chongzuo, consisting of teeth ascribed to P. weidenreichi.[22][23] Pongo is found as part of the faunal complex in the Pleistocene cave assemblage in Vietnam, alongside Giganopithecus, though it is known only from teeth. Some fossils described under the name P. hooijeri have been found in Vietnam, and multiple fossil subspecies have been described from several parts of southeastern Asia. It is unclear if these belong to P. pygmaeus or P. abelii or, in fact, represent distinct species.[24] During the Pleistocene, Pongo had a far more extensive range than at present, extending throughout Sundaland and mainland Southeast Asia and South China. Teeth of orangutans are known from Peninsular Malaysia that date to 60,000 years ago. The range of orangutans had contracted significantly by the end of the Pleistocene, most likely due to the reduction of forest habitat during the Last Glacial Maximum.[25] Though they may have survived into the Holocene in Cambodia and Vietnam.[22]

Genomics

 
Flanged male Bornean, Sumatran and Tapanuli orangutans

The Sumatran orangutan genome was sequenced in January 2011.[26][27] Following humans and chimpanzees, the Sumatran orangutan became the third species of hominid to have its genome sequenced. Subsequently, the Bornean species had its genome sequenced. Genetic diversity was found to be lower in Bornean orangutans (P. pygmaeus) than in Sumatran ones (P. abelii), despite the fact that Borneo is home to six or seven times as many orangutans as Sumatra.[27]

The comparison has shown these two species diverged around 400,000 years ago, more recently than was previously thought. Also, the orangutan genome was found to have evolved much more slowly than chimpanzee and human DNA.[27] Previously, the species was estimated to have diverged 2.9 to 4.9 mya.[15](Fig. 4) The researchers hope these data may help conservationists save the endangered ape, and also prove useful in further understanding of human genetic diseases.[27] Of the great apes, orangutans, gorillas, and chimpanzees have 48 diploid chromosomes in contrast to humans which have 46.[28]:9

However, nuclear DNA sequence comparisons reported in 2017 suggested that the Bornean and Tapanuli orangutans diverged from Sumatran orangutans about 3.4 million years ago, and from each other around 2.4 million years ago. Orangutans travelled from Sumatra to Borneo as the islands were connected by land bridges as parts of Sundaland during recent glacial periods when sea levels were much lower. The present range of Tapanuli orangutans is thought to be close to the point where ancestral orangutans first entered what is now Indonesia from mainland Asia.[21][29]

Appearance and anatomy

 
Adult male (left) and female

Orangutans display significant sexual dimorphism; females typically stand 115 cm (3 ft 9 in) tall and weigh around 37 kg (82 lb), while flanged adult males stand 137 cm (4 ft 6 in) tall and weigh 75 kg (165 lb). Compared to humans, they have proportionally long arms, a male orangutan having arm span of about 2 m (6.6 ft), and short legs. Most of their bodies are covered in coarse hair that is generally red but ranges from bright orange to maroon or dark chocolate, while the skin is grey-black. Though largely hairless, their faces can develop some hair in males, giving them a beard.[30][31][14]:14

 
The orangutan's skeleton is well adapted for its arboreal lifestyle.

Orangutans have small ears and noses, the former being unlobed. The braincase is elevated relative to the facial area which is concave and prognathous. Females and juveniles have rounded skulls and narrow faces while males develop a large sagittal crest and large cheek flaps,[30] which show their dominance to other males. The cheek flaps are made mostly of fatty tissue and are supported by the musculature of the face.[32] Mature males also develop large throat pouches and long canines.[30][14]:14

As in all Old World Primates, orangutan hands are similar to human hands; they have four long fingers, but a dramatically shorter opposable thumb for strong branch gripping as they travel high in the trees. The joint and tendon arrangement in the orangutans' hands produces two adaptations that are significant for arboreal locomotion. The resting configuration of the fingers is curved, creating a suspensory hook grip. Additionally, with the thumb out of the way, the fingers (and hands) can grip securely around objects with a small diameter by resting the tops of the fingers against the inside of the palm, thus creating a double-locked grip.[33]

Their feet have four long toes and an opposable big toe, enabling orangutans to securely grasp things both with their hands and with their feet. Since their hip joints have the same flexibility as their shoulder and arm joints, orangutans have less restriction in the movements of their legs than humans have.[14]:14–15

Unlike gorillas and chimpanzees, orangutans are not true knuckle-walkers, but are instead fist-walkers. Knuckle-walkers use a more relaxed open hand with the middle segments of the fingers sweeping the ground while fist-walking happens with a more gripped fist so the closest finger segments (that one might punch with) touch the ground.[34]

Compared to their relatives in Borneo, Sumatran orangutans are thinner with paler and longer hair and longer face.[31] Tapanuli orangutans resemble Sumatran orangutans more than Bornean orangutans in body build and fur color.[21] However, they have frizzier hair, smaller heads, and flatter and wider faces than the other species.[35]

Ecology and behaviour

Wild orangutan in the Danum Valley (Sabah, Malaysia, Borneo island)

Orangutans are mainly arboreal and inhabit tropical rainforest, particularly dipterocarp and secondary old growth forest.[31][36] Population densities are highest in habitats near rivers, such as freshwater and peat swamp forest, while drier forest away from the flood plains are less inhabited. In addition, population density also decreases at higher elevations.[28]:82 Orangutans occasionally enter grasslands, cultivated fields, gardens, young secondary forest, and shallow lakes.[36]

Most of the day is spent feeding, resting, and travelling.[37] They start the day feeding for 2–3 hours in the morning. They rest during midday then travel in the late afternoon. When evening arrives, they begin to prepare their nests for the night.[36] Orangutans do not swim, although they have been recorded wading in water.[38]:80 Potential predators of orangutans include tigers, clouded leopards and wild dogs.[28]:80 The absence of tigers on Borneo has been suggested to be a reason why Bornean orangutans are found on the ground more often than their Sumatran relatives.[31] The most frequent parasites of orangutan are nematodes of the genus Strongyloides and the ciliate Balantidium coli. Among Strongyloides, the species S. fuelleborni and S. stercoralis are commonly reported in young individuals.[39]

Diet and feeding

 
Although orangutans may consume leaves, shoots, and even bird eggs, fruit is the most important part of their diet.

Orangutans are primarily frugivores (fruit-eaters) and 57–80% of their feeding time is spent foraging for fruits. Even during times of scarcity, fruit can still take up 16% of feeding. Orangutans prefer fruits with soft pulp, arils or seed-walls surrounding their seeds, as well as trees with large crops. Ficus fruits fit both preferences and are thus highly favoured but they also consume drupes and berries.[28]:47–48 Orangutans are thought to be the sole fruit disperser for some plant species including the climber species Strychnos ignatii that contains the toxic alkaloid strychnine.[40]

Orangutans also supplement their diet with leaves, which take up 25% of their foraging time on average. Leaf eating increases when fruit gets scarcer but even during times of fruit abundance, orangutan will eat leaves 11–20% of the time. The leaf and stem material of Borassodendron borneensis appears to be an important food source during low fruit abundance. Other food items consumed by the apes include bark, honey, bird eggs, insects and small vertebrates including the slow loris.[36][28]:48–49

A decade-long study of urine and faecal samples at the Gunung Palung Orangutan Conservation Project in West Kalimantan has shown that orangutans give birth during and after the high fruit season (though not every year), during which they consume various abundant fruits, totalling up to 11,000 calories per day. In the low-fruit season, they eat whatever fruit is available in addition to tree bark and leaves, with daily intake at only 2,000 calories.[41]

In some areas, orangutans may practice geophagy, which involves consuming soil and other earth substances. The apes may eat tubes of soil created by termites along tree trunk as well as descend to the ground to uproot soil to eat. Orangutans are also known to visit mineral licks at the clay or sandstone-like walls of cliffs or earth depressions. Soils appear to contain a high concentration of kaolin, which counteracts toxic tannins and phenolic acids found in the orangutan's diet.[28]:49–50 Orangutans also use plants of the genus Commelina as an anti-inflammatory balm.[42]

Social life

 
Orangutans are the least social of the great apes.

Orangutans live a more solitary lifestyle than the other great apes. Most social bonds occur between adult females and their dependent and weaned offspring. Adult males and independent adolescents of both sexes tend to live alone. Orangutan societies are made up of resident and transient individuals of both sexes. Resident females live with their offspring in defined home ranges that overlap with those of other adult females, which may be their immediate relatives. One to several resident female home ranges are encompassed within the home range of a resident male, who is their main mating partner. Transient males and females move widely.[43][44] Bornean orangutans tend to be more solitary, moving and foraging alone while Sumatran orangutans travel in groups more often.[31] The social structure of the orangutan can be best described as solitary but social. Interactions between adult females range from friendly to avoidance to antagonistic.[45] Adult males dominate sub-adult males.[46]

During dispersal, females tend to settle in home ranges that overlap with their mothers. However, they do not seem to have any special social bonds with them.[44] Males disperse much farther from their mothers and enter into a transient phase. This phase lasts until a male can challenge and displace a dominant, resident male from his home range.[47] Both resident and transient orangutans aggregate on large fruiting trees to feed. The fruits tend to be abundant, so competition is low and individuals may engage in social interactions.[48][49] Orangutans will also form travelling groups with members moving between different food sources.[47] These groups tend to consist of only a few individuals. They also tend to be consortships between an adult male and female.[48]

Orangutans communicate with various sounds. Males will make long calls, both to attract females and to advertise themselves to other males.[50] Long calls are divided into three parts; they begin with grumbles, climax with pulses and end with bubbles. Both sexes will try to intimidate conspecifics with a series of low guttural noises known collectively as the "rolling call". When annoyed, an orangutan will suck in air through pursed lips, making a kissing sound known as the "kiss squeak". Mothers produce throatcrapes to keep in contact with their offspring. Infants make soft hoots when distressed. Orangutans are also known to produce smacks or blow raspberries when making a nest.[51]

Nesting

 
Orangutans build elaborate nests with "pillows", "blankets", "bunk-beds" and "roofs".

Orangutans build nests specialised for either day or night use. These are carefully constructed; young orangutans learn from observing their mother's nest-building behaviour. In fact, nest-building is a leading cause in young orangutans leaving their mother for the first time. From six months of age onwards, orangutans practice nest-building and gain proficiency by the time they are three years old.[52]

Construction of a night nest is done by following a sequence of steps. Initially, a suitable tree is located, orangutans being selective about sites though many tree species are used. The nest is then built by pulling together branches under them and joining them at a point. After the foundation has been built, the orangutan bends smaller, leafy branches onto the foundation; this serves the purpose of and is termed the "mattress". After this, orangutans stand and braid the tips of branches into the mattress. Doing this increases the stability of the nest and forms the final act of nest-building. In addition, orangutans may add additional features, such as "pillows", "blankets", "roofs" and "bunk-beds" to their nests.[52]

Reproduction and development

Flanged male orangutan
Unflanged male orangutan

Males become sexually mature at around age 15. However, they may exhibit arrested development by not developing the distinctive cheek pads, pronounced throat pouches, long fur, or long-calls until a resident dominant male is absent. The transformation from unflanged to flanged can occur very quickly. Flanged males attract oestrous females with their characteristic long calls, which may also suppress development in younger males. Unflanged males wander widely in search of oestrous females and upon finding one, will force copulation on her. While both strategies are successful, females prefer to mate with flanged males and seek their company for protection. Resident males may form consortships that last days, weeks or months after copulation.[53][46][50][47][14]:100

 
Mother orangutan with young

Like other great apes, female orangutans are infertile during adolescence, which may last up to four years. They first ovulate at 5.8 to 11.1 years (earlier in those with more body fat) and have a 22- to 30-day menstrual cycle. Gestation lasts nine months, with a first birth at age 14 or 15.[54][55] Female orangutans have 6–9 year intervals between births, the longest interbirth intervals among the great apes.[56] Unlike many other primates, male orangutans do not seem to practice infanticide. This may be because they cannot ensure they will sire a female's next offspring because she does not immediately begin ovulating again after her infant dies.[57]

Male orangutans play almost no role in raising the young. Females do most of the caring and socialising of the young. A female often has an older offspring with her to help in socialising the infant.[58] Infant orangutans are completely dependent on their mothers for the first two years of their lives. The mother will carry the infant during travelling, as well as feed it and sleep with it in the same night nest.[14]:100 For the first four months, the infant is carried on its belly and never relieves physical contact. In the following months, the time an infant spends with its mother decreases.[58]

When an orangutan reaches the age of two years, its climbing skills improve and it will travel through the canopy holding hands with other orangutans, a behaviour known as "buddy travel".[58] After two years of age juvenile orangutans and will start to temporarily move away from their mothers and are weaned four years old. They reach adolescence at six or seven years of age and will socialise with their peers while still having contact with their mothers.[14]:100 Typically, orangutans live over 30 years both in the wild and in captivity.[14]:14

Intelligence and cognition

Faux-speech produced by an orangutan

Orangutans are among the most intelligent non-human primates. Experiments suggest they can figure out some invisible displacement problems with a representational strategy.[59] In addition, Zoo Atlanta has a touch-screen computer where their two Sumatran orangutans play games. Scientists hope the data they collect will help researchers learn about socialising patterns, such as whether the apes learn behaviours through trial and error or by mimicry, and point to new conservation strategies.[60]

A 2008 study of two orangutans at the Leipzig Zoo showed orangutans can use "calculated reciprocity", which involves weighing the costs and benefits of gift exchanges and keeping track of these over time. Orangutans are the first nonhuman species documented to do so.[61] In a 1997 study, two captive adult orangutans were tested with the cooperative pulling paradigm. Without any training the orangutans succeeded in the first session. Over the course of 30 sessions, the apes succeeded more quickly, having learned to coordinate.[62] An adult orangutan has been documented to pass the mirror test, indicting self-awareness.[63] However, mirror tests with a 2-year-old orangutan failed to reveal self-recognition.[64]

Studies in the wild indicate that flanged male orangutans plan their movements in advance and signal them to other individuals.[65] Orangutans are very technically adept nest builders, making a new one in only five or six minutes and choosing branches they know can support their body weight.[66]

Orangutans and other great apes show laughter-like vocalisations in response to physical contact such as wrestling, play chasing or tickling. This suggests that laughter derived from a common origin among primate species, and therefore evolved prior to the origin of humans.[67] Orangutans have also been found to have voluntary control over vocal fold oscillation, which is essential for speech in humans, and can learn and mimic new sounds.[68][69]

Tool use and culture

 
An orangutan at the San Diego Zoo using precision grip

Tool use in orangutans was observed by primatologist Birutė Galdikas in ex-captive populations.[70] In addition, evidence of sophisticated tool manufacture and use in the wild was reported from a population of orangutans in Suaq Balimbing (Pongo abelii) in 1996.[71] These orangutans developed a tool kit for use in foraging which consisted of both insect-extraction tools for use in the hollows of trees and seed-extraction tools for harvesting seeds from hard-husked fruit. The orangutans adjusted their tools according to the nature of the task at hand, and preference was given to oral tool use.[72] This preference was also found in an experimental study of captive orangutans (P. pygmaeus).[73]

Primatologist Carel P. van Schaik and biological anthropologist Cheryl D. Knott further investigated tool use in different wild orangutan populations. They compared geographic variations in tool use related to the processing of Neesia fruit. The orangutans of Suaq Balimbing (P. abelii) were found to be avid users of insect and seed-extraction tools when compared to other wild orangutans.[74][75] The scientists suggested these differences are cultural. The orangutans at Suaq Balimbing live in dense groups and are socially tolerant; this creates good conditions for social transmission.[74] Further evidence that highly social orangutans are more likely to exhibit cultural behaviours came from a study of leaf-carrying behaviours of ex-captive orangutans that were being rehabilitated on the island of Kaja in Borneo.[76]

Wild orangutans (P. pygmaeus wurmbii) in Tuanan, Borneo, were reported to use tools in acoustic communication. They use leaves to amplify the kiss squeak sounds they produce. The apes may employ this method of amplification to deceive the listener into believing they are larger animals.[77] In 2003, researchers from six different orangutan field sites who used the same behavioural coding scheme compared the behaviours of the animals from the different sites. They found the different orangutan populations behaved differently. The evidence suggested the differences were cultural: first, the extent of the differences increased with distance, suggesting cultural diffusion was occurring, and second, the size of the orangutans' cultural repertoire increased according to the amount of social contact present within the group. Social contact facilitates cultural transmission.[78]

Possible linguistic capabilities

A study of orangutan symbolic capability was conducted from 1973 to 1975 by zoologist Gary L. Shapiro with Aazk, a juvenile female orangutan at the Fresno City Zoo (now Chaffee Zoo) in Fresno, California. The study employed the techniques of psychologist David Premack, who used plastic tokens to teach linguistic skills to the chimpanzee, Sarah.[79] Shapiro continued to examine the linguistic and learning abilities of ex-captive orangutans in Tanjung Puting National Park, in Indonesian Borneo, between 1978 and 1980.[80]

During that time, Shapiro instructed ex-captive orangutans in the acquisition and use of signs following the techniques of psychologists R. Allen Gardner and Beatrix Gardner, who taught the chimpanzee, Washoe, in the late 1960s. In the only signing study ever conducted in a great ape's natural environment, Shapiro home-reared Princess, a juvenile female, which learned nearly 40 signs (according to the criteria of sign acquisition used by psychologist Francine Patterson with Koko, the gorilla) and trained Rinnie, a free-ranging adult female orangutan, which learned nearly 30 signs over a two-year period.[80] For his dissertation study, Shapiro examined the factors influencing sign learning by four juvenile orangutans over a 15-month period.[81]

Interactions with humans

Orangutans were known to the native people of Sumatra and Borneo for millennia. While some communities hunted them for food and decoration, others placed taboos on such practices. In central Borneo, some traditional folk beliefs consider it bad luck to look in the face of an orangutan. Some folk tales involve orangutans mating with and kidnapping humans. There are even stories of hunters being seduced by female orangutans.[14]:66–71 Europeans became aware of the existence of the orangutan possibly as early as the 17th century.[14]:68 European explorers in Borneo hunted them extensively during the 19th century. The first accurate description of orangutans was given by Dutch anatomist Petrus Camper, who observed the animals and dissected some specimens.[14]:64–65

 
Orangutan researcher Birutė Galdikas presenting her book about orangutans

Field studies

Little was known about orangutan behaviour until the field studies of Birutė Galdikas,[82] who became a leading authority on the apes. When she arrived in Borneo, Galdikas settled into a primitive bark-and-thatch hut, at a site she dubbed Camp Leakey, near the edge of the Java Sea.[83] Despite numerous hardships, she remained there over 30 years and became an outspoken advocate for orangutans and the preservation of their rainforest habitat, which is rapidly being devastated by loggers, palm oil plantations, gold miners, and unnatural forest fires.[84] Galdikas's conservation efforts have extended well beyond advocacy, largely focusing on rehabilitation of the many orphaned orangutans turned over to her for care.[83] Galdikas is considered to be one of Leakey's Angels, along with Jane Goodall and Dian Fossey.[85]

In fiction

Orangutans first appeared in Western fiction in the 18th century and have been used to comment on human society. Written by the pseudonymous A. Ardra, Tintinnabulum naturae (The Bell of Nature, 1772) is told from the point of view of a human-orangutan hybrid who calls himself the "metaphysician of the woods". Over half a century later, the anonymously written work "The Orang Outang" is narrated by a pure orangutan in captivity in the US, writing to her friend in Java and critiquing Boston society.[6]:108–109 Thomas Love Peacock’s 1817 novel Melincourt features Sir Oran Hautto, an orangutan who participates in English society and becomes a candidate for Member of Parliament. The novel satirises the class and political system of Britian and Oran’s reliability, honesty and status as a "natural man" stand in contrast to the cowardice, greed, folly, and inequality of "civilised" human society.[6]:110–111 In Frank Challice Constable's The Curse of Intellect (1895), the protagonist Reuben Power travels to Borneo to capture and train an orangutan "to know what a beast like that might think of us".[6]:114–115 Orangutans are prominently featured in the 1963 science fiction novel Planet of the Apes by Pierre Boulle and the media franchise that derived from it. Orangutans are typically portrayed as bureaucrats like Dr. Zaius, the science minister.[6]:118–119, 175–176

Orangutans are sometimes portrayed as villains, notably in the 1832 Walter Scott novel Count Robert of Paris and the 1841 Edgar Allan Poe short story The Murders in the Rue Morgue. In the case of the latter, the ape was trained to murder by his human master.[6]:145 Disney's 1967 animated musical adaptation of The Jungle Book added an orangutan named King Louie, voiced by Louis Prima, who tries to get Mowgli to teach him how to make fire.[6]:266 The 1986 horror film Link features an intelligent orangutan who serves a university professor but has sinister motives, particularly with his stalking of a student assistant.[6]:174–175 Some stories have portrayed orangutans as guides to humans, such as The Librarian in Terry Pratchett's fantasy novels Discworld and in Dale Smith's 2004 novel What the Orangutan Told Alice.[6]:145 More comical portrayals of the orangutan include the 1996 film Dunston Checks In.[6]:181

In captivity

 
The Female Orang – Utan (Jenny sitting in a chair)[86]

By the early 19th century, orangutans were being shipped to captive facilities at various locations. In 1817, an orangutan joined several other animals in London's Exeter Exchange. The ape was recorded to have shunned the company of other animals, aside from a dog, and appeared to prefer the company of humans. It was occasionally taken on coach rides dressed in a smock-frock and hat and even treated with refreshments at an inn where it impressed its host with its polite behaviour.[6]:64–65 The London Zoo housed a female orangutan named Jenny who wore human clothing and learned to drink tea. She is remembered for her meeting with the naturalist Charles Darwin who compared her reactions to those of a human child.[86][87]

Zoos and circuses in the Western world would continue to use orangutans and other simians as sources for entertainment, training then to behave like humans in tea parties and preforming tricks. Notable orangutan "character actors" include Jacob and Rosa of the Tierpark Hagenbeck in the early 20th century and Jiggs of the San Diego Zoo in the 1930s and 1940s.[6]:187–189, 193–194 Animal rights groups have urged a stop to such acts, considering them abusive.[88] Starting in the 1960s, zoos become more concern with education and orangutans exhibits tried to mimic their natural environment and displayed their natural behaviours.[6]:185, 206 Ken Allen, an orangutan of the San Diego Zoo, became world famous in the 1980s for multiple escapes from his enclosures. He was nicknamed "the hairy Houdini" and was the subject of a fan club, T-shirts, bumper stickers and a song titled The Ballad of Ken Allen.[89]

Galdikas reported that her cook was sexually assaulted by a captive male orangutan.[90] Being raised in captivity, the ape may have suffered from a skewed species identity, and forced copulation is a standard mating strategy for low-ranking male orangutans.[91]

Legal status

In December 2014, Argentina became the first country to recognise a non-human primate as having legal rights when it ruled that an orangutan named Sandra at the Buenos Aires Zoo must be moved to a sanctuary in Brazil in order to provide her "partial or controlled freedom". Animal rights groups like Great Ape Project Argentina interpreted the ruling as applicable to all species in captivity, and legal specialists from the Argentina's Federal Chamber of Criminal Cassatio considered the ruling applicable only to non-human hominids.[92]

Conservation

Status and threats

 
Deforestation for palm oil production in Indonesia. Most logging in Indonesia is performed illegally.[93]

All three species are critically endangered according to the IUCN Red List of mammals.[94][95][96] The Bornean orangutan range has become patchy throughout the island, being largely extirpated from various parts of the island, including the southeast.[95] The largest remaining population is found in the forest around the Sabangau River, but this environment is at risk.[97] Sumatran orangutan is found only in the northern part of Sumatra, with most of the population inhabiting the Leuser Ecosystem.[94] The Tapanuli orangutan is found only in the Batang Toru forest of Sumatra.[96]

Estimates between 2000 and 2003 found 7,300 Sumatran orangutans[94] and between 45,000 and 69,000 Bornean orangutans[95] remain in the wild. A 2007 study by the Government of Indonesia noted a total wild population of 61,234 orangutans, 54,567 of which were found on the island of Borneo in 2004.[98][99] A 2016 study estimates a population of 14,613 Sumatran orangutans in the wild, doubling previous population estimates.[100] It is estimated that fewer than 800 Tapanuli orangutan still exist, which puts the species among the most endangered of great apes.[101][35] The table below shows a breakdown of the species and subspecies and their estimated populations from this, or (in the case of P. tapanuliensis) a more recent, report:[99][98][100]

A video of orangutans at a rehabilitation centre in Borneo
Scientific
name
Common
name
Region Estimated
number
Pongo abelii Sumatran orangutan Sumatra 14,613
Pongo tapanuliensis Tapanuli orangutan Sumatra (Lake Toba region) <800
Pongo pygmaeus Bornean orangutan Borneo
P. p. morio Northeast Bornean orangutan Sabah 11,017
East Kalimantan 4,825
P. p. wurmbii Central Bornean orangutan Central Kalimantan >31,300
P. p. pygmaeus Northwest Bornean orangutan West Kalimantan and Sarawak 7,425

During the early 2000s, orangutan habitat has decreased rapidly due to logging and forest fires, as well as fragmentation by roads. A major factor has been the conversion of vast areas of tropical forest to palm oil plantations in response to international demand. Hunting is also a major problem as is the illegal pet trade.[94][95] Orangutans may be killed for the bushmeat trade[102] and bones are secretly traded in souvenir shops in several cities in Kalimantan, Indonesia.[103] Mother orangutans are killed so their infants can be sold as pets, and many of these infants die without the help of their mother.[104] Since 2012, authorities, with the aid of the Orangutan Information Center, confiscated 114 orangutans, 39 of which were pets.[105]

A female orangutan was rescued from a village brothel in Kareng Pangi village, Central Kalimantan, in 2003. The orangutan was shaved and chained for sexual purposes. Since being freed, the orangutan, named Pony, has been living with the Borneo Orangutan Survival Foundation (BOSF). She has been re-socialised to live with other orangutans.[106] In May 2017, the BOSF rescued an albino organgutan from captivity. The rare primate was being held captive in a remote village in Kapuas Hulu, on the island of Kalimantan in the Indonesian Borneo. According to volunteers at BOSF, albino orangutans are extremely rare (one in ten thousand). This is the first albino orangutan the organisation has seen in 25 years of activity.[107]

Conservation centres and organisations

 
Zoologische Gesellschaft Frankfurt Programm Director Peter Pratje works with orangutans in Bukit Tigapuluh, Indonesia.

A number of organisations are working for the rescue, rehabilitation and reintroduction of orangutans. The largest of these is the Borneo Orangutan Survival Foundation, founded by conservationist Willie Smits and operates a number of large projects, such as the Nyaru Menteng Rehabilitation Program founded by conservationist Lone Drøscher Nielsen.[108][109][110]

Other major conservation centres in Indonesia include those at Tanjung Puting National Park, Sebangau National Park, Gunung Palung National Park and Bukit Baka Bukit Raya National Park in Borneo and the Gunung Leuser National Park and Bukit Lawang in Sumatra. In Malaysia, conservation areas include Semenggoh Wildlife Centre and Matang Wildlife Centre also in Sarawak, and the Sepilok Orang Utan Sanctuary in Sabah.[111] Major conservation centres headquartered outside the orangutans' home countries include Frankfurt Zoological Society,[112] Orangutan Foundation International, which was founded by Birutė Galdikas,[113] and the Australian Orangutan Project.[114]

Conservation organisations such as Orangutan Land Trust work with the palm oil industry to improve sustainability and encourages the industry to establish conservation areas for orangutans.[115] It works to bring different stakeholders together to achieve conservation of the species and its habitat.[116]

See also

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