Classified in the genus Pongo, orangutans were considered to be one species. However, since 1996, they have been divided into two species ;
In addition, the Bornean species is divided into three subspecies. Based on genome sequencing, the two extant orangutan species evidently diverged around 400,000 years ago. The orangutans are also the only surviving species of the subfamily Ponginae, which also included several other species, such as the three extinct species of the genus Gigantopithecus, including the largest known primate Gigantopithecus blacki. The ancestors of the Ponginae subfamily split from the main ape line in Africa 16 to 19 million years ago (mya) and spread into Asia.
Orangutans are the most arboreal of the great apes and spend most of their time in trees. Their hair is typically reddish-brown, instead of the brown or black hair typical of chimpanzees and gorillas. Males and females differ in size and appearance. Dominant adult males have distinctive cheek pads and produce long calls that attract females and intimidate rivals. Younger males do not have these characteristics 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. The live up to 50 years in both the wild and captivity, sometimes longer given specific circumstances.
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 and occasionally day nests. The apes have been extensively studied for their 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. Deforestation caused by humans have seen severe declines in the populations and ranges of both species. Threats to wild orangutan populations include poaching, habitat destruction, and the illegal pet trade.
The name "orangutan" is derived from the Malay and Indonesian words orang meaning "person" andhutan meaning "forest", thus "person of the forest". Orang Hutan was originally not used to refer to apes, but to forest-dwelling humans. The Malay words used to refer specifically to the ape are maias and mawas, but it is unclear if those words refer to just orangutans, or to all apes in general. Dutch physician Jacobus Bontius' 1631 Historiae naturalis et medicae Indiae orientalis – described that Malaysians had informed him the ape was able to talk, but preferred not to "lest he be compelled to labour".
The name of the genus, Pongo, comes from a 16th-century account by Andrew Battell, 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 late 18th century, all great apes were believed to be orangutans, hence Lacépède's use of Pongo for the genus.
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, andSivapithecus, 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. 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.
The orangutan's skeleton is adapted for its arboreal lifestyle.
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 more sparse and lighter-coloured coats. Though largely hairless, their faces can develop some hair in males, giving them a moustache. Adult males have large cheek flaps to 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' throat pouches allow them to make loud calls. The females can grow to around 127 cm (4 ft 2 in) and weigh around 45.4 kg (100 lb), while flanged adult males can reach 175 cm (5 ft 9 in) in height and weigh over 118 kg (260 lb). A male orangutan has an arm span of about 2 m (6.6 ft).
Orangutan hands are similar to human 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. Their feet have four long toes and an opposable big toe. 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. Unlike gorillas and chimpanzees, orangutans are not true knuckle-walkers, and are instead fist-walkers.
Ecology & 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 at elevations as high as 1500 m while Bornean orangutans live no higher than 1000 m. 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 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 nests for the night. Orangutans do not swim, although they have been recorded wading in water.
Although orangutans may consume leaves, shoots, and even bird eggs, fruit is the most important part of their diet.
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, making a kissing sound that is hence known as the "kiss squeak". Infants make soft hoots when distressed. Orangutans are also known to blow raspberries.
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 and 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 & 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, 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. 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 also use plants of the genus Commelina as an anti-inflammatory balm.
Orangutans are the least social of the great apes, but individuals do commonly interact.
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. 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 interactions. Orangutans will also form travelling groups with members moving between different food sources. These groups tend to be made of only a few individuals.
Orangutans build nests specialized for both 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.
Orangutans build elaborate nests which have "pillows", "blankets", "bunk-beds" and "roofs".
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.
Reproduction and parenting
Males mature at around 15 years of age, by which time they have fully descended testicles and can reproduce. However, they exhibit arrested development by not developing 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 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 against unflanged males. Resident males may form consortships with females that can last days, weeks or months after copulation.
Infants cling to their mothers for the first four months. 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– to 30-day menstrual cycle. Gestation lasts for 9 months, with females giving birth to their first offspring between the ages of 14 and 15 years. 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 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 travelling, 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 an infant spends with its mother decreases.] When an orangutan reaches the age of two, its climbing skills improve and it will travel through the canopy holding hands with other orangutans, a behaviour known as "buddy travel". Orangutans are juveniles from 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 they can figure out some invisible displacement problems with a representational strategy. Orangutans are very technically adept nest builders, making a new nest each evening in only in 5 to 6 minutes and choosing branches which they know can support their body weight.
Tool use and culture
Captive orangutans may use objects in creative ways. 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.
Tool use has been investigated in different wild orangutan populations. A comparison of geographic variations in tool use related to the processing of Neesia fruit was conducted. 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 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 they produce. The apes may employ this method of amplification to deceive the listener into believing 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 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.
Orangutans and Native people of Sumatra & Borneo
Orangutans were known to the native people of Sumatra and Borneo for millennia. While some communities hunted them for food and decoration & Initiation Rites, 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.
A persistent folktale on Sumatra and Borneo and in popular culture, is that male orangutans display sexual attraction to human women, and may even forcibly copulate with them. The only serious, but anecdotal, report of such an incident taking place, is primatologist Birutė Galdikas' report that her cook was sexually assaulted by a male orangutan. This orangutan, though, was raised in captivity and may have suffered from a skewed species identity, and forced copulation is a standard mating strategy for low-ranking male orangutans. A case has been reported of a brothel village keeping a shaved and chained female orangutan for sexual purposes.
In December 2014, Argentina became the first country to recognize 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." Although animal rights groups interpreted the ruling as applicable to all species in captivity, legal specialists considered the ruling only applicable to hominid apes due to their genetic similarities to humans.
The Sumatran species is critically endangered and the Bornean species 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 from various parts of the island, including the southeast. 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.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.