Orangutan

Fossil skull of Sivapithecus sivalensis, a possible ancestor of orangutans

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 in 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 be 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.[17]^:50

The oldest known record of Pongo is from the early Pleistocene of Chongzuo, consisting of teeth ascribed to P. weidenreichi.[20][21] 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.[22] 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 because of the reduction of forest habitat during the Last Glacial Maximum.[23] Though they may have survived into the Holocene in Cambodia and Vietnam.[20]

Flanged male Bornean, Sumatran and Tapanuli orangutans

The Sumatran orangutan genome was sequenced in January 2011.[24][25] 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. The researchers hope these data may help conservationists save the endangered ape, and also prove useful in further understanding of human genetic diseases.[25] Similarly to gorillas and chimpanzees, orangutans have 48 diploid chromosomes, in contrast to humans, which have 46.[26]^:9

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. Israfil et al (2011) estimated that the Sumatran and Borean species diverged 2.9 to 4.9 mya.[27]^{(Fig. 4)} By contrast, the 2011 genome study suggested that 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.[25] However a 2017 found that the Bornean and Tapanuli orangutans diverged from Sumatran orangutans about 3.4 mya, and from each other around 2.4 mya. 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 where ancestral orangutans first entered what is now Indonesia from mainland Asia.[18][28]

Although orangutans may consume leaves, shoots, and 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.[26]^:47–48 Orangutans are thought to be the sole fruit disperser for some plant species including the climber species Strychnos ignatii which contains the toxic alkaloid strychnine.[41]

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][26]^:48–49 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 trunks 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.[26]^:49–50

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.[42]

Orangutans are the least social of the great apes.

The social structure of the orangutan can be best described as solitary but social; they 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 often live alone. Orangutan societies comprise 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.[43][44] Bornean orangutans are generally more solitary, moving and foraging alone while Sumatran orangutans travel in groups more often.[31] Interactions between adult females range from friendly to avoidance to antagonistic.[45] The home ranges of resident males can overlap greatly, though encounters are relatively rare and hostile.[46] Adult males dominate sub-adult males.[47]

Orangutans disperse and establish their home ranges by age 11. Females tend to settle close to their mothers. However, they do not seem to have any special social bonds with them.[44][48] Males disperse much farther but may include their natal (birth) range within their new home range.[48] They enter a transient phase, which lasts until a male can challenge and displace a dominant, resident male from his home range.[49] 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.[50][51] Orangutans will also form travelling groups with members moving between different food sources.[49] These groups usually consist of only a few individuals. They also tend to be consortships between an adult male and a female.[50] Social grooming is uncommon among orangutans.[52]

Orangutans communicate with various sounds. Males will make long calls, both to attract females and to advertise themselves to other males.[53] These 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 throatscrapes 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.[54]

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 quickly. Flanged males attract females in oestrous 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 can be successful, females prefer to mate with flanged males and seek their company for protection. However, in some areas females prefer unflanged males during times of instability and do not resist copulations. Resident males may form consortships that last for days, weeks or months after copulation.[55][47][53][49][17]^: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.[56][57] Female orangutans have a six to nine year interberth interval, the longest among the great apes.[48] 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.[58] However, there is evidence that females with offspring under six years old generally avoid adult males.[59]

Females do most of the caring and socialising of the young, while males play no role. A female often has an older offspring with her to help socialise the infant.[52] Usually only a single infant is born; twins are a rare occurrence.[60] Infant orangutans completely depend on their mothers for the first two years of their lives. The mother will carry the infant while travelling, and feed it and sleep with it in the same night nest.[17]^:100 For the first four months, the infant is carried on its belly and almost never without physical contact. In the following months, the time an infant spends with its mother decreases. When an orangutan reaches the age of one-and-a-half years, its climbing skills improve and it will travel through the canopy holding hands with other orangutans, a behaviour known as "buddy travel".[52] After two years of age, juvenile orangutans will begin to move away from their mothers temporarily and are weaned at 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.[17]^:100 Typically, orangutans live over 30 years both in the wild and in captivity.[17]^:14

An orangutan lying in its nest

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 ability is a leading cause for young orangutans to regularly leave their mother. From six months of age onwards, orangutans practice nest-building and gain proficiency by the time they are three years old.[61]

Construction of a night nest is done by following a sequence of steps. Initially, a suitable tree is located. Orangutans are 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 is the final act of nest-building. Orangutans may add additional features, such as "pillows", "blankets", "roofs" and "bunk-beds" to their nests.[61]

An orangutan at the San Diego Zoo using precision grip

Tool use in orangutans was observed by primatologist Birutė Galdikas in ex-captive populations.[75] 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.[76] 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 task at hand, and preference was given to oral tool use.[77] This preference was also found in an experimental study of captive orangutans (P. pygmaeus).[78]

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.[79][80] The scientists suggested these differences are cultural as they do not correlate with habitat. The orangutans at Suaq Balimbing live in dense groups and are socially tolerant; this creates good conditions for social transmission.[79] Further evidence that highly social orangutans are more likely to exhibit cultural behaviours came from a study of leaf-carrying behaviours of formerly captive orangutans that were being rehabilitated on the island of Kaja in Borneo.[81]

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.[82] In 2003, researchers from six different orangutan field sites who used the same behavioural coding scheme compared the behaviours of the animals from each site. They found each orangutan population 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.[83]

Zoologist Gary L. Shapiro conducted a study of orangutan symbolic capability from 1973 to 1975 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.[84] 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.[85]

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 first 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.[85] For his dissertation study, Shapiro examined the factors influencing sign learning by four juvenile orangutans over a 15-month period.[86]

Little was known about orangutan behaviour until the field studies of Birutė Galdikas,[87] 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 Java Sea.[88] 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.[89] Galdikas's conservation efforts have extended well beyond advocacy, largely focusing on rehabilitation of the many orphaned orangutans turned over to her for care.[88] Along with Jane Goodall and Dian Fossey, Galdikas is considered to be one of Leakey's Angels.[90]

Illustration for Murders on Morgue Street by Daniel Vierge

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 Parliament. The novel satirises the class and political system of Britain. 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 featured prominently in the 1963 science fiction novel Planet of the Apes by Pierre Boulle and the media franchise 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 where 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 which 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

The Female Orang – Utan (Jenny sitting in a chair)[91]

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.[91][92]

Zoos and circuses in the Western world would continue to use orangutans and other simians as sources for entertainment, training them to behave like humans at tea parties and to perform 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.[93] Starting in the 1960s, zoos became more concerned with education and orangutans exhibits were designed 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.[94] Galdikas reported that her cook was sexually assaulted by a captive male orangutan.[95] The ape may have suffered from a skewed species identity and forced copulation is a standard mating strategy for low-ranking male orangutans.[96]

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 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.[97]

All three species are critically endangered according to the IUCN Red List of mammals.[98][99][100] The Bornean orangutan range has become patchy throughout the island, being largely extirpated from various parts of the island, including the southeast.[99] The largest remaining population is found in the forest around the Sabangau River, but this environment is at risk.[101] The Sumatran orangutan is found only in the northern part of Sumatra, with most of the population inhabiting the Leuser Ecosystem.[98] The Tapanuli orangutan is found only in the Batang Toru forest of Sumatra.[100]

Deforestation for palm oil production in Indonesia. Most logging in Indonesia is done illegally.[102]

During the early 2000s, orangutan habitat has decreased rapidly because of logging and forest fires, and 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.[98][99] Orangutans may be killed for the bushmeat trade[103] and bones are secretly traded in souvenir shops in several cities in Indonesian Borneo.[104] Mother orangutans are killed so their infants can be sold as pets, and many of these infants die without the help of their mother.[105] Since 2012, the Indonesian authorities, with the aid of the Orangutan Information Center, confiscated 114 orangutans, 39 of which were pets.[106]

Estimates between 2000 and 2003 found 7,300 Sumatran orangutans[98] and between 45,000 and 69,000 Bornean orangutans[99] remain in the wild.[107] A 2016 study estimates a population of 14,613 Sumatran orangutans in the wild, doubling previous population estimates.[108] Fewer than 800 Tapanuli orangutan are estimated to still exist, which puts the species among the most endangered of the great apes.[109][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:[107][110][108]

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 (BOS) Foundation, founded by conservationist Willie Smits which operates a number of large projects, such as the Nyaru Menteng Rehabilitation Program founded by conservationist Lone Drøscher Nielsen.[111][112][113] 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 BOS. She has been re-socialised to live with other orangutans.[114] In May 2017, the BOS rescued an albino orangutan from captivity. The rare primate was being held captive in a remote village in Kapuas Hulu, on the island of Kalimantan in Indonesian Borneo. According to volunteers at BOS, albino orangutans are extremely rare (one in ten thousand). This is the first albino orangutan the organisation has seen in 25 years of activity.[115]

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.[116] Major conservation centres headquartered outside the orangutans' home countries include Frankfurt Zoological Society,[117] Orangutan Foundation International, which was founded by Birutė Galdikas,[118] and the Australian Orangutan Project.[119] Conservation organisations such as the Orangutan Land Trust work with the palm oil industry to improve sustainability and encourages the industry to establish conservation areas for orangutans.[120] It works to bring different stakeholders together to achieve conservation of the species and its habitat.[121]