|Lacépède , 1799|
The orangutans ( Pongo ) is a primate genus in the family of great apes (hominids). They differ from the other great apes by their red-brown fur and their physique, which is more adapted to a tree-dwelling way of life. They live on the Southeast Asian islands of Sumatra and Borneo ; the populations of both islands are now managed as three separate species: Bornean orangutan ( Pongo pygmaeus ), Sumatran orangutan ( Pongo abelii ) and the newly discovered Tapanuli orangutan ( Pongo tapanuliensis ).
Orangutans reach a head-to-trunk length of 1.25 to 1.5 meters. With regard to weight, there is a clear gender dimorphism : males weigh 50 to 90 kilograms, almost twice as heavy as females who weigh 30 to 50 kilograms. Animals in captivity, on the other hand, tend to become significantly heavier, with males reaching a weight of almost 200 kilograms. The Sumatran orangutans are generally lighter and more delicate than their relatives in Borneo. The rather thin and shaggy-looking fur of the orangutans is dark red or reddish brown in color - usually a little lighter in the animals from Sumatra.
The limbs of these animals show strong specializations in a tree-dwelling way of life. The arms are very long and strong and can reach a wingspan of 2.25 meters. The hands are hook-shaped and elongated, while the thumb is very short and located close to the wrist. The comparatively short legs are very flexible and can be bent inwards, which is useful for vertical climbing on tree trunks. The big toe is shortened like the thumb and placed relatively close to the tarsus, while the other toes are elongated and curved. Overall, this gives the feet a hand-like impression.
Head and teeth
The head of the orangutans is characterized by the high, rounded skull and the protruding, arched snout. In contrast to the African great apes, the bulges above the eyes are only weakly pronounced and the eyes are small and close together. However, like those of the gorillas, the skulls of the males are equipped with sagittal and nuchal ridges (bulges on the top of the head and neck), which serve as muscle attachment points. Both sexes have a beard, the Sumatran type being longer. Male animals are also equipped with a throat pouch, which is particularly large in the Bornean species. Adult males have noticeable cheek bulges, these grow all life and are most pronounced in old animals. In Borneo orangutans these bulges grow outward and are almost hairless, in Sumatran orangutans they lie flat on the head and are covered with white hair.
Like all Old World monkeys , orangutans have 32 teeth, the tooth formula is I 2- C 1- P 2- M 3. The central incisors are large, while the outer teeth are pin-shaped and small. The canines of the males are significantly larger than those of the females; The molars are characterized by low cusps and a strongly curled chewing surface, which is an adaptation to the often hard-shelled food.
distribution and habitat
A million years ago, orangutans were found in large areas of Southeast Asia. Their original range reached from southern China via Thailand, Vietnam to Java, which is proven by fossil finds in southern China , Vietnam and the island of Java . In parts of this area they are likely to have survived at least until a few thousand years ago. On Java they lived in the Dutch colonial times, on the mainland they lived in prehistoric times.
Today orangutans only occur on the islands of Borneo and Sumatra . On Sumatra they inhabit the north-western regions and parts of the west coast, on Borneo they are mainly found in the southern and eastern regions.
Way of life
Activity times and movement
Like all great apes, orangutans are diurnal. They have two activity highlights, one in the morning and one in the late afternoon, and they stop at lunchtime. When they sleep, they build a nest out of branches and leaves. The altitude offers the orangutans protection from predators and parasites. Usually they build a new nest every night, occasionally the same one is used twice. Orangutans curl up to sleep and are late risers compared to other primates. For the observation of orangutans, counting the sleeping nests is an essential method of surveying the population.
They are predominantly tree dwellers. There they move mainly by slowly climbing with all four limbs or walking on the branches - but their movements are more leisurely than those of the gibbons, for example . Especially when they are in a hurry, they swing on their long arms ( brachiation ). In order to get from one tree to another, you can make them swing violently in order to reduce the distance.
Orangutans rarely come to the ground. Often times, this is only done to get from one tree to another, their movements being careful and timid. Adult males, on the other hand, can sometimes even make forays on the ground. This behavior is more common in the Bornean species, probably because, unlike Sumatra, there are no tigers there. Their locomotion on the surface of the earth is four-footed walking; In contrast to the African great apes ( chimpanzees and gorillas ) they do not move in the ankle gait , but support themselves either on the fists or on the inner edges of the hands.
Territorial and migratory behavior
Orangutans have multiple territorial strategies and can be referred to as "resident animals", "commuters" and "wanderers".
"Resident animals" inhabit fixed territories. In females, these cover around 70 to 900 hectares and can overlap with the territories of other females. The territories of the males are much larger with 4,000 to 5,000 hectares and mostly overlap with those of several females. The length of the daily forays depends on the size of the area; however, they are not only used for food intake, but in males also for contact with the females or the search for possible male competitors.
However, the majority of male orangutans do not establish a fixed territory, but move around as “commuters” or “wanderers”. “Commuters” only stay in an area for a few weeks or months and change their location several times a year. They can often be found in the same areas again the following year. The whereabouts of the “commuters” can be several kilometers apart, and the forays of these animals are accordingly significantly longer than those of the resident orangutans. Young adult males are mostly "hikers", they are never to be found in an area for long, but move around constantly. As they get older, they can sometimes establish a permanent territory or remain hikers for their entire life.
Orangutans can usually be found individually, and there are only permanent bonds between females and young animals. Nevertheless, these animals interact with conspecifics and do not lead a strictly solitary way of life, but the details of these social relationships are not yet fully known.
Encounters between males are usually hostile. They call attention to themselves; direct encounters can also lead to fights. Females, on the other hand, react more peacefully to one another, sometimes in pairs for several days in search of food. In general, Sumatran orangutans are more social than Borneo orangutans ; there have been observations of larger groups of this type and also temporary associations of a male with a female and their young.
Resident animals are likely to have a higher social rank than those who roam, which is evident from the different reproductive strategies , among other things . Lower-ranking, wandering males often force breeding with females. Victims of this forced copulation, sometimes anthropomorphically referred to as "rape", are mostly young or lower-ranking females. Resident males, on the other hand, monitor the females living in their territory during their forays in order to protect them from forced copulations. Because of the higher rank of these males, the females are likely to consent to mating.
Orangutans are calmer than other great apes. More noticeable sounds are the loud cries of the males. These serve to point out other males of their territory and to establish contact with females. Due to the larger throat pouch, the screams of the Bornean orangutans are louder and longer than those of the Sumatran orangutans. Little is known about other phonetic expressions or communication using facial expressions and postures.
The use of tools is less common in orangutans in the wild than in chimpanzees, for example . But animals have been observed using wooden sticks to dig, fight, or scratch themselves with. To get to the tasty seeds of Neesia fruits, which are embedded in a fruit bowl with stinging hair, orangutans make matching wooden sticks out of thin twigs. They protect themselves from rain and blazing sun with large leaves that they hold over their heads.
The comparatively low use of tools could also be due to the rather solitary way of life of these animals, which makes the conditions for the transmission of acquired behavior more difficult. This also agrees with observations that tool use is far more common in the more social Sumatran orangutans than in the Bornean orangutans.
With earlier in the Zoological Garden Osnabrück captive Sumatran orangutans (eg. Putting together of the metal rods) could in laboratory studies demonstrated that the animals are able not only to use tools, but also to produce simple tools thereby reaching a goal like food.
The most significant natural enemy of the Sumatran orangutans is the Sumatran tiger . The Sunda clouded leopard , which lives on Sumatra and Borneo , is dangerous for adolescent animals and females, but is generally unable to kill adult males. Crocodiles and feral domestic dogs sometimes pose additional threats .
Orangutans are mainly herbivores. At around 60%, fruits represent the largest part of their diet, and they often eat fruits with hard skins or seeds. They also eat leaves, young shoots, and bark. Animal food only plays a subordinate role. Occasionally, however, they eat insects, bird eggs and small vertebrates. The Sumatian species seem to have a slightly larger proportion of animals in their diet than the Borneos. By spreading the seeds of the fruits eaten, they play a role in the reproduction of some plants.
When eating, they either sit or hang on the branches, their body weight bending them down, making it easier for them to get to fruit or leaves. Their strong arms allow them to bend over thick fruit-bearing branches or sometimes even to break them off.
During the fattening years in dipterocarp forests, which occur every 2 to 10 years , they can eat far more food than usual. It is created as a fat store for times of lack of food. This predisposition may be one reason why orangutans have a tendency to become obese in captivity.
Reproduction and development
Mating and birth
Orangutans do not have a fixed mating season; reproduction can occur all year round. However, it can depend on the food supply, so that several females in one region give birth to their young almost simultaneously. The length of the sexual cycle is around 28 days, the estrus lasts around 5 to 6 days, the females show no normal swelling .
As noted above, there are two strategies of reproduction, forced copulation by roving males and voluntary mating with resident males. In one study, each of the two strategies provided around half of the offspring. After a gestation period of around eight to nine months (average 245 days), the female usually gives birth to a single young, twins are rare. Newborns weigh around 1.5 to 2 kilograms. The birth interval is seven to eight years, making it the longest of all great apes.
Development of the young animals
The rearing of the young is the sole responsibility of the female, the male is not involved. In the first months of life, the newborn clings to the mother's belly and up to the age of two it is carried on the forays, provided with food by her and sleeps in the same nest. At the age of two to five years the young animal begins to develop its climbing skills, it begins to explore its surroundings without losing sight of contact, and it learns to build a nest. In the same period - at around 7 years of age - it is weaned.
At the age of five to eight years, the increasing separation from the mother sets in. They still have frequent contact with her, but in this phase they often seek contact with their peers and form alliances with them. During this time it can happen that a female has two children around her, an adolescent and a newborn.
Sexual maturity and life expectancy
Females reach sexual maturity at around seven years of age, with males this is likely to be more variable and occur at eight to 15 years of age. After the final separation from the mother, the females try to establish their own territory, often close to the mother's territory. However, it takes a few years before they reproduce for the first time, usually from the age of 14.
After the onset of sexual maturity, males usually go through a longer period than "wanderers". During this time they are capable of procreation (and force copulations), but outwardly they hardly differ from females. The typical secondary sexual characteristics such as cheek bulges and throat sacs do not appear until much later, approximately between the ages of 15 and 20. The appearance of these traits is often related to the establishment of their own territory or the absence of other males. If they manage to establish their own territory, these characteristics develop quickly, often within a few months.
Due to their low reproductive rate, females often give birth to only two to three young animals in their life, and menopause in captive animals occurs at around 48 years of age. Life expectancy in the wild is estimated to be up to 50 years. Animals in human care grow older and can reach 60 years of age.
Orangutans together with the gorillas , the chimpanzees ( Common Chimpanzee and Bonobo ) and the people , the family of great apes (hominids). They form the sister group of the other species and are led in their own subfamily, Ponginae, which is opposite to the Homininae. This is also geographically clear, since the other great apes live in Africa or come from there. This is expressed in the cladogram (right).
There are some extinct primates that are now in the Pongini tribe and are thus interpreted as relatives of the orangutan ancestors. These include Sivapithecus / Ramapithecus , Khoratpithecus , Ankarapithecus , Lufengpithecus and probably also Meganthropus and Gigantopithecus .
Traditionally, both populations living on separate islands were considered to be subspecies of a common species. Genetic studies at the end of the 20th century, however, indicated a division into two species, which resulted in the splitting of the Sumatran orangutan ( Pongo abelii ) from the Bornean orangutan ( Pongo pygmaeus ) in 2001. Both are now recognized as separate species. In addition to genetic data, this division can now also be justified by differences in body structure and lifestyle. The Bornean species is divided into two or three subspecies, Pongo pygmaeus pygmaeus , Pongo pygmaeus wurmbii and sometimes also Pongo pygmaeus morio , which differ in terms of the structure of the skull. Further genetic studies on the orangutans from Sumatra could not show them as a monophyletic group, as a population south of Lake Toba is more closely related to the Bornean orangutan. This led to the description of the Tapanuli orangutan ( Pongo tapanuliensis ) in 2017 .
The extinct orangutans from different regions of Southeast Asia, some of which were significantly larger than today's animals, have been described as different species, such as Pongo palaeosumatrensis ( Sumatra ), Pongo weidenreichi (southern China and Vietnam ) and Pongo hooijeri (also Vietnam). Their taxonomic status and their relationship to today's species is controversial.
The development of the genus orangutan ( Pongo ) took place in Asia (while Homo primarily in Africa developed). According to molecular genetic studies, the Sumatran orangutan ( Pongo abelii ) first split off from the line of the original orangutans; this took place in the Pliocene around 3.4 million years ago. Today it is common north of Lake Toba on Sumatra. The second line includes the Tapanuli orangutan ( Pongo tapanuliensis ), which occurs south of Lake Toba , and the Bornean orangutan ( Pongo pygmaeus ) from the island of Borneo. The two only separated from each other in the Middle Pleistocene 674,000 years ago.
Due to progressive drought, recurring glaciations and changes in monsoon activity , the habitat of the tropical rainforest on the Asian continent shifted towards the equator since the late Miocene and Pleistocene . In the Pleistocene, the genus was widespread around 60,000 years ago in Malaysia, and 40,000 years ago in the region from southern China to Java. The consequences of the climate-related withdrawal can still be seen today in the genetic distribution patterns of the Bornean orangutan ( Pongo pygmaeus ) on the Pleistocene refuge Sumatra-Borneo. However, the perception of the refugee area Borneo is being questioned.
Orangutans and humans
The term “orangutan” comes from the Malay words “orang” (human) and “utan” or “hutan” (forest) and therefore means “forest man”. This name appeared in European languages for the first time in 1631. According to Brehms Tierleben , “the Javanese […] claim that the monkeys could talk if they only wanted to, but would not because they feared having to work.” In local languages of the Region, the terms maias or mawas are also used .
The orangutans of Sumatra were initially described as a separate species in the 19th century , later the systematic that was valid until the end of the 20th century was established, which considered the populations of both islands as subspecies of a common species. The differences in physique and behavior, combined with molecular studies, resulted in them being listed as two separate species today.
The scientific name of the genus Pongo goes back to the English navigator Andrew Battell (around 1565-1614). In his "Report on Angola and the neighboring regions" (1613) he described two "monsters" (presumably gorilla and chimpanzee ), the larger of which the locals called "Pongo" and the smaller of which they called "Engeco".
Battell's travelogue was often quoted and reprinted many times, with the result that Pongo (see: M'Pungu ) was used for decades as the overarching term for all great apes "discovered" by Europeans at the time. For example, Immanuel Kant wrote in his Physical Geography in 1802 :
- “The orangutan, the forest man, of which the largest in Africa are called Pongos. They can be found in Congo, Java, Borneo and Sumatra, always walk upright and are six feet high. [...] There is also a smaller genus which the English call chimpanzees [...]. "
Arthur Schopenhauer put it in a similarly cross-species way in 1819 when he was thinking about the intelligence of the great apes:
- “It has gradually become certain that the extremely intelligent orangutan is a young pongo who, when grown, loses the great human resemblance of the face and at the same time the astonishing intelligence [...] and in their place an extraordinary muscle strength develops, which , as sufficient for its maintenance, the great intelligence now makes superfluous. "
On the other hand, called Jean-Baptiste Lamarck in 1809 reversed the African chimpanzees and the Asian great apes as orangutans :
- "The orang of Angola (Simia troglodytes, Lin.) Is the most perfect of all animals: it is more perfect than the Indian orang (Simia satyrus, L.), which has been called orangutang."
The nomenclature confusion within the great apes was not cleared up until the 19th century; it is mainly due to the fact that hardly any of the early European naturalists had previously seen a live great ape and had not been able to make a single comparison of living specimens of orangutans, gorillas and chimpanzees.
The orangutan was the godfather of the common name given to the crab Achaeus japonicus with its orange-brown-red "hair" , which is referred to in several European languages as the orangutan crab .
It was not until the second half of the 20th century that field studies began to investigate the behavior of these animals in the wild. The best-known researcher in this context is Birutė Galdikas .
As with the other great apes, laboratory tests are carried out on orangutans to investigate the intelligence and communication skills of these animals. The 20-year-old orangutan Chantek in the Atlanta Zoo (US state Georgia) became famous here . In contrast to the great outdoors, where tools are rarely used, the use of tools can often be observed in animals in captivity. They also manage to solve tricky problems, such as opening a box closed with buckles and containing a ripe fruit. Their intelligence, dexterity and strength also enable them to overcome negligently constructed safety mechanisms in zoos and to break out of enclosures.
As part of the research into communication skills, orangutans were taught to communicate using a symbolic language.
The range of the orangutans has declined sharply since the Pleistocene . Today all three species are seriously threatened. The reasons for this lie primarily in the destruction of their habitat, as well as in hunting and trading - especially with young animals. These factors are exacerbated by the slow reproduction rate of the animals.
The main threat today is the destruction of their habitat. Forests are being cleared to a large extent, on the one hand to produce wood, on the other hand to establish agricultural land. Recently, the strong demand for palm oil is increasingly endangering orangutan habitats. Malaysia and Indonesia , the two countries where orangutans live, are among the main producers of this product.
Hunting is another factor. In some areas - for example in the interior of Borneo - their meat is eaten. In addition, in some places they are deliberately tracked when they enter orchards in search of food. Their size and rather leisurely movements make them an easy target for hunters. In addition, young animals are caught and sold as pets, which is usually associated with the killing of the mother. Orangutans were smuggled into Taiwan in the 1990s , perhaps under the influence of a television show that featured an orangutan as the "ideal pet". According to an estimate from 2002, two animals are smuggled out of Borneo every week. Since orangutans are listed in the Washington Convention on Endangered Species (CITES), such practices are illegal.
In addition, these animals are at risk from disease transmission. Due to their close relationship with humans, they can contract hepatitis , cholera , malaria and tuberculosis , which are transmitted, for example, through the numerous contacts in national parks with rangers and tourists.
Both on Sumatra and in the Malaysian and Indonesian parts of Borneo there are protected areas and national parks for the endangered fauna of the region. Some reintroduction stations have also been set up to prepare confiscated young animals for life in the wild.
On Sumatra, wild orangutans can only be found in the forests of the two northern provinces of Aceh and North Sumatra, many of them in the Gunung Leuser National Park . Orangutans have been under protection for more than 60 years. Indonesian law forbids them to be killed, captured, held, or traded in. Nevertheless, numerous animals end up on the black market and in private households every year.
The PanEco Foundation has been campaigning for the survival of the orangutans in Sumatra with the Sumatran Orangutan Protection Program SOCP since 1999. Together with the Indonesian nature conservation authority PHKA, the Yayasan Ekosistem Lestari YEL Foundation (Foundation for a Sustainable Ecosystem) and the Frankfurt Zoological Society , orangutans illegally held in captivity are confiscated and reintroduced into their natural habitat. A release station is located in the Bukit Tigapuluh National Park in Jambi Province . There have been no orangutans here since the 19th century, although the forest is a suitable habitat for these animals. Resettlement is possible here because, according to IUCN guidelines, no animals may be released in areas that still contain wild populations. For this reason, the Bohorok Rehabilitation Center in North Sumatra, founded in the 1970s, had to be closed, which had been releasing confiscated orangutans into the Gunung Leuser National Park for three decades. At the beginning of 2011, the PanEco Foundation was able to open a second reintroduction station in the Jantho nature reserve in the northernmost province of Aceh. All animals confiscated in Aceh are released back into the wild here. In addition to the reintroduction of orangutans, the monitoring of orangutan populations, research into the behavior of wild orangutans, environmental education and public relations work are among the core tasks of the PanEco Foundation in Sumatra. Their main goal is to protect and preserve the tropical rainforest.
The Borneo Orangutan Survival Foundation (BOS) runs two rehabilitation projects in Borneo , both in the Indonesian part of the island: Nyaru Menteng and Samboja Lestari . These projects are supported by Borneo Orangutan Survival Germany , BOS Switzerland and other organizations in cooperation with the Indonesian BOS Foundation .
Other protected areas are among others in Gunung Palung National Park , in the Tanjung Puting and in Kutai National Park . The largely associated with Malaysia North Borneo introduces two rearing and reintroduction centers: the Sepilok Orang Utan Rehabilitation Center in Sandakan in the state of Sabah and the more compact outside Kuching located Semenggoh -Reservat in Sarawak . Another important sanctuary for Bornean orangutans in Malaysia is the Danum Valley Conservation Area , which is also in Sabah. In the 1990s, the Borneo Orangutan Survival Foundation released 350 orangutans into the Meratus sanctuary. There the ALT Foundation runs a joint conservation project with the support of the Borneo Orangutan Aid.
Stock figures and degree of risk
Estimates of the total orangutan population are difficult. Transect surveys on Sumatra in 2015 resulted in an extrapolation of 13,846 Sumatran orangutans, significantly more than in old estimates. The population of Bornean orangutans is estimated at 104,700. There are only 800 specimens left of the Tapanuli orangutans.
The IUCN lists both the species on Sumatra and the species on Borneo as " critically endangered ".
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