The orangutans are the two exclusively Asian species of extant great apes. Native to Indonesia and Malaysia, orangutans are currently found only in the rainforests of Borneo and Sumatra. Classified in the genus Pongo, there are only two surviving species: the Bornean orangutan (P. pygmaeus) and the Sumatran orangutan (P. abelii). They are also the only surviving species of the subfamily Ponginae, which also included several other species like Gigantopithecus.
The largest living arboreal animals, they have proportionally longer arms than the other, more terrestrial, great apes. Their hair is typically reddish-brown, instead of the brown or black hair typical of chimpanzees and gorillas. Dominant adult males have distinctive cheek pads. Orangutans are the more solitary of the great apes, with most social bonds occurring between mothers and their dependent offspring. Fruit is the most important component of a orangutans diet, however, the apes will also eat vegetation, bark, honey, insects and even bird eggs. They are among the most intelligent primates and use a variety of sophisticated tools, also making sleeping nests each night from branches and foliage. The apes have been extensively studied for their and learning abilities. There may even be distinctive cultures within populations.
Both orangutan species are considered to be Endangered with the Sumatran orangutan being Critically Endangered. Threats to orangutan populations include poaching, habitat destruction and the illegal pet trade.
Taxonomy and phylogeny
The two 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 (million years ago), and Sivapithecus, which lived India and Pakistan from 12.5 mya until 8.5 mya. These apes likely lived in drier and cooler environments then 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. It is likely that great ape evolution was centered in Africa and the lineage that lead to the Asian apes split off around 20 mya, and orangutans arose in that lineage around 11–14 mya.:50
- Genus Pongo
The populations on the two islands were classified as subspecies until 1996:53, when they were elevated to full species status, 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). Regardless, the type locality of pygmaeus has not been established beyond doubts, and may be from the population currently listed as wurmbii (in which case wurmbii would be a junior synonym of pygmaeus, while one of the names currently considered a junior synonym of pygmaeus would take precedence for the northwest Bornean taxon). To further confuse, the name morio, as well as some suggested junior synonyms, may be junior synonyms of the pygmaeus subspecies, thus leaving the east Bornean populations unnamed.
In addition, 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.
Orangutans have 48 diploid chromosomes, and its genome was sequenced in January 2011. Following humans and chimpanzees, the Sumatran orangutan has become the third species of hominid to have its genome sequenced. The researchers also published less complete copies from ten wild orangutans, five from Borneo and five from Sumatra. It was found that genetic diversity was 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 comparison has shown that these two species diverged around 400,000 years ago, more recently than was previously thought. It was also found that the orangutan genome has evolved much more slowly than chimpanzee and human DNA.
Anatomy and physiology
An orangutan has a large, bulky body, a thick neck, very long, strong arms, short, bowed legs, and no tail. It is mostly covered with long reddish-brown hair and grey-black skin. Sumatran orangutans have the more sparse and lighter coloured coat. The orangutan has a large head with a prominent mouth area. Though largely hairless, the face of orangutan can develop some hair in males, giving them a moustache. Adult males have large cheek flaps:14 that show their dominance to other males. The cheek flaps are made mostly of fatty tissue and are supported by the musculature of the face. Mature males also have throat pouches that allows them to make loud calls.:14 There is significant sexual dimorphism: females can grow to around 4 ft 2 in (127 cm) and weigh around 100 lb (45 kg) while flanged adult males can reach 5 ft 9 in (175 cm) in height and weigh over 260 lb (118 kg).
Orangutan hands are similar to humans' hands; they have four long fingers and an opposable thumb. However, 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.:301 Additionally, without the use of the thumb, the fingers and hands can grip tightly around objects with a small diameter by resting the tops of the fingers against the inside of the palm, which creates a double-locked grip.:301
Their feet have four long toes and an opposable big toe.:15 Orangutans can grasp things with both their hands and their feet. A male orangutans has an arm span of about 2 m (6.6 ft).:14 Their fingers and toes are curved, allowing them to better grip onto branches. Orangutans have less restriction in the movements of their legs than humans since their hips joint have the same flexibility as their shoulder and arm joints.:15 Unlike gorillas and chimpanzees, orangutans are not true knuckle-walkers, and are instead fist-walkers.
Typically, orangutans live over 30 years in both the wild and captivity.:14
Ecology and behaviour
Orangutans live in primary and old secondary forests, particularly dipterocarp forests and peat swamp forests. Both species can be found in mountainous and lowland swampy areas. Sumatran orangutans live in elevations as high as 1500 m (4921 ft), while Bornean orangutans live no higher than 1000 m (3281 ft). Other habitats used by orangutans include grasslands, cultivated fields, gardens, young secondary forest, and shallow lakes. Orangutans are the most arboreal of the great apes, spending nearly all of their time in the trees. Most of the day is spent feeding, resting, and travelling. 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 nest for the night. Orangutans do not swim, although they have been recorded wading in water.
The main predators of orangutans are tigers. Other predators include clouded leopards, wild dogs and crocodiles. The absence of tigers on Borneo may explain why Bornean orangutans can be found on the ground more often than their Sumatran relatives. Orangutans communicate with various sounds. Male will make long calls, both to attract females and advertise themselves to other males. 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, which makes a kissing sound and is hence known as the "kiss squeak". Infants make soft hoots when distressed. Orangutans are also known to blow a raspberry.
Orangutans are opportunistic foragers, and their diets vary markedly from month to month. Fruit makes up 65–90% of the orangutan diet, and those with sugary or fatty pulp are favoured. Ficus fruits are commonly eaten, because they are easy to harvest and digest. Lowland dipterocarp forests are preferred by orangutans because of their plentiful fruit. Bornean orangutans consume at least 317 different food items that include young leaves, shoots, bark, insects, honey and bird eggs.
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, totaling 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. Together with a long lactation period, orangutans also have a long birth interval.
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. It does not appear to have any effect on orangutans except for excessive saliva production.
Geophagy, the practice of eating soil or rock, has been observed in orangutans. There are three main reasons for this dietary behaviour; for the addition of mineral nutrients to their diet; for the ingestion of clay minerals that can absorb toxic substances; or to treat a disorder such as diarrhoea.
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, who 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. Orangutans usually travel alone, but they may travel in small groups in their sub-adult years. However this behaviour ends at adulthood. 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. Resident males may have overlapping ranges and interactions between them tend to be hostile.
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. 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. Adult males dominate sub-adult males. 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 intereactions. Orangutans will also form traveling groups with members moving between different food sources. These groups tend to be made of only a few individuals. They also tend to be consortships between an adult male and female.
Orangutans build day as well as night nests. 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.
Construction of a night nest is done by following a sequence of steps. Initially a suitable tree is located, orangutans being selective about sites even though many tree species are utilised. The foundation 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 as the "mattress". After this orangutans stand and braid the tips of branches into the mattress. 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 nest.
Reproduction and parenting
They mature at around 15 years of age by which time they have fully descended testicles and can reproduce. However they exhibit arrested development and do not develop the distinctive cheek pads, pronounced throat pouches, long fur or long-calls until they are between 15 and 20 years old. The development of these characteristics depends largely on the absence of a resident male. Males without them are known as unflanged males in contrast to the more developed flanged males. The transformation from unflanged to flanged can occur very quickly. Unflanged and flanged males have two different mating strategies. Flanged males attract oestrous females with their characteristic long calls. Those calls may also suppress development in younger males. Unflanged males wander widely in search of estrous females and upon finding one, will force copulation on her. Both strategies are successful, however females prefer to mate with flanged males and seek their company for protection against unflanged males. Resident males may form consortships with females that can last days, weeks or months after copulation.
Female orangutans experience their first ovulatory cycle around 5.8–11.1 years. These occur earlier in females with more body fat. Like other great apes, female orangutans enter a period of infertility during adolescence which may last for 1–4 years. Female orangutans also have a 22–30 day menstrual cycle. Gestation lasts for nine months with females giving birth to their first offspring between 14 and 15 years old. Female orangutans have eight year intervals between births; the longest interbirth intervals among the great apes. Unlike many other primates, male orangutans do not seem to practice infanticide. This may be because they cannot ensure that they will sire a female's next offspring because she does not immediately begin ovulating again after her infant dies.
Male orangutans play almost no role in raising the young. Females do most of the caring and socializing of the young. A female often has an older offspring with her to help in socializing the infant. Infant orangutans are completely dependent on their mothers for the first two years of their lives. The mother will carry the infant during traveling, as well as feed it and sleep with it in the same night nest. For the first four months, the infant is carried on its belly and never relieves physical contact. In the following months, the time a infant spends with its mother decreases. When an orangutan reaches the age of two, its climbing skills improve and will travel through the canopy holding hands with other orangutans, a behaviour known as "buddy travel". Orangutans are juveniles for about two to five years of age and will start to temporarily move away from their mothers. Juveniles are usually weaned at about four years of age. Adolescent orangutans will socialize with their peers while still having contact with their mothers.
Orangutans are among the most intelligent primates. Experiments suggest that they can figure out some invisible displacement problems with a representational strategy. In addition, Zoo Atlanta has a touch screen computer where their two Sumatran orangutans play games. Scientists hope that the data they collect from this will help researchers learn about socializing patterns, such as whether they mimic others or learn behaviour from trial and error, and hope the data can point to new conservation strategies. A 2008 study of two orangutans at the Leipzig Zoo showed that orangutans are the first non-human species documented to use 'calculated reciprocity' which involves weighing the costs and benefits of gift exchanges and keeping track of these over time.
Tool use and culture
Tool use in orangutans was observed by German primatologist Birutė Galdikas in ex-captive populations. 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. These orangutans developed a tool kit for use in foraging that 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. This preference was also found in an experimental study of captive orangutans (P. pygmaeus).
Carel P. van Schaik from the University of Zurich and Cheryl D. Knott from Harvard University 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. The scientists suggested that these differences are cultural. The orangutans at Suaq Balimbing live in dense groups and are socially tolerant; this creates good conditions for social transmission. 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.
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 that they produce. Some have suggested that the apes employ this method of amplification in order to deceive the listener into believing that they are larger animals.
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 that the different orangutan populations behaved differently. The evidence suggested that the differences in behaviour were cultural: first, because the extent of the differences increased with distance, suggesting that cultural diffusion was occurring, and second, because the size of the orangutans' cultural repertoire increased according to the amount of social contact present within the group. Social contact facilitates cultural transmission.
Possible lingustic capabilities
A two year study of orangutan symbolic capability was conducted from 1973 to 1975 by 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 David Premack who used plastic tokens to teach linguistic skills to the chimpanzee, Sarah. 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. During that time, Shapiro instructed ex-captive orangutans in the acquisition and use of signs following the techniques of R. Allen 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 who learned nearly 40 signs (according to the criteria of sign acquisition used by Francine Patterson with Koko, the gorilla) and trained Rinnie, a free-ranging adult female orangutan who learned nearly 30 signs over a two year period. For his dissertation study, Shapiro examined the factors influencing sign learning by four juvenile orangutans over a 15-month period.
Orangutans and humans
Orangutans were known to the native people of Sumatra and Borneo for millennia. The name "orangutan", comes from the Malay "orang" (man) and "(h)utan" (forest, wild); hence, "man of the woods." While some communities hunted them for food and decoration, others placed taboos on such practices.:66 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.:68 There are even stories of hunters being seduced by female orangutans.:71 Europeans became aware of the existence of the orangutan possibly as early as the 17th century.:68 European explorers in Borneo hunted orangutans extensively during the 19th century.:65 The first accurate description of orangutans was given by Dutch anatomist Petrus Camper, who observed the animals and dissected some specimens.:64 However, little was known about orangutans until the field studies of Birutė Galdikas.
Male orangutans have been reported to display sexual attraction to human women to the point of rape. The cook of noted primatologist Birutė Galdikas was raped by an orangutan. According to reporter Carole Jahme, rape "was almost the fate of Julia Roberts" when she was seized by a male orangutan before being freed by the film crew.
The Sumatran species is critically endangered and the Bornean species of orangutan is endangered according to the IUCN Red List of mammals, and both are listed on Appendix I of CITES. The Bornean orangutan population declined by 50% in the past 60 years. Its range has become patchy throughout Borneo: being largely extirpated form various parts of the island, including the south-east. The largest remaining population is found in the forest around the Sabangau River, but this environment is at risk. Sumatran orangutan populations declined by 80% in 75 years. This species is now found only in the northern part of Sumatra, with most of the population inhabiting the Leuser Ecosystem.
Estimates between 2000 and 2003 found that 7,300 Sumatran orangutans and between 45,000 and 69,000 Bornean orangutans remain in the wild. A 2007 study by the Government of Indonesia noted in 2004 it was estimated that there was a total wild population of 61,234 orangutans, 54,567 of which were found on the island of Borneo. The table below shows a breakdown of the species and subspecies and their estimated populations from the report:
|Pongo abelii||Sumatran orangutan||Sumatra||6,667|
|Pongo pygmaeus||Bornean orangutan||Borneo|
|P. p. morio||Northeast Bornean orangutan||Sabah||11,017|
|P. p. morio||Northeast Bornean orangutan||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|
Orangutan habitat destruction due to logging and forest fires, as well as fragmentation by roads, has been increasing rapidly in the last decade. A major factor in that period of time has been the conversion of vast areas of tropical forest to oil palm plantations in response to international demand. Palm oil is used for cooking, cosmetics, mechanics, and biodiesel. There is also a major problem with hunting and the illegal pet trade. Orangutans may be killed for the bushmeat trade, crop protection or for use for traditional medicine. Orangutan bones are secretly traded in souvenir shops in several cities in Kalimantan, Indonesia. Mother orangutans are killed so their infants can be sold as pets, and many of these infants die without the help of their mother. Since 2004, several pet orangutans were confiscated by local authorites and sent to rehabilitation centres.
Conservation centres and organisations
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. It is audited by a multinational auditor company and operates under the formal agreement with the Indonesian Ministry of Forest to conserve and rehabilitate orangutans. It operates a number of large projects, including the Samboja Lestari Forest Rehabilitation Program and the Nyaru Menteng Rehabilitation Program managed by Lone Drøscher Nielsen.
Other major conservation centres in Indonesia include those at Tanjung Puting National Park and Sebangau National Park in Central Kalimantan, Kutai in East Kalimantan, Gunung Palung National Park in West Kalimantan, and Bukit Lawang in the Gunung Leuser National Park on the border of Aceh and North Sumatra. In Malaysia, conservation areas include Semenggoh Wildlife Centre in Sarawak and Matang Wildlife Centre also in Sarawak, and the Sepilok Orang Utan Sanctuary near Sandakan in Sabah.
Conservation organizations such as Orangutan Land Trust work with local communities to promote sustainable production of palm oil and encourage the industry to establish conservation areas. They also aim to fiance these activities with revenue from carbon offset programs.
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