Orangutan
Pongo
TAXONOMY
Suborder: Haplorrhini
Infraorder: Simiiformes
Superfamily: Hominoidea
Family: Hominidae
Genus: Pongo
Species: P. abelii, P. pygmaeus
Subspecies: P. p. morio, P. p. pygmaeus, P. p. wurmbii
Other names: orangoutan (French); orango (Italian); maias or mawas (Malay); orangután (Spanish); orangutang (Swedish); P. pygmaeus: Bornean orangutan; P. abelii: Sumatran orangutan
Translated from Malay, orangutan means "person of the forest," but it is also used to denote a madman or savage human and is not the word for orangutan used by local people (Rijksen 1978). The Malay word for orangutan is maias or mawas (Rijksen 1993).
MORPHOLOGY
Genetically diverging 1.5 million years ago, phenotypic differences between the two species of orangutan are apparent. Sumatran orangutans are thinner than their Bornean relatives, have paler red coats, longer hair, and longer faces. Adult males have mustaches and prominent cheek pads, called flanges, that are covered with fine, white hair. Both sexes have long beards (Courtenay et al. 1988; Rowe 1996). Bornean orangutans have coarse, long hair that can be orange, brown, or maroon. Infants are born with pink faces but as they age, the pigment changes to dark brown or almost black skin. Males have large, pendulous throat pouches and, compared to the Sumatran species, their cheek pads are markedly larger, covered in short bristly hair (Courtenay et al. 1988; Rowe 1996). Males and females of both species are highly sexually dimorphic, with males weighing, on average, 87 kg (192 lb) and measuring 970 mm (3.18 ft) and females weighing, on average, 37 kg (81.6 lb) and measuring 780 mm (2.56 ft) (Markham & Groves 1990; Rowe 1996).
Pongo pygmaeus
Orangutans climb using both hands and both feet to hold onto branches as they move horizontally through the rain forest canopy (Rodman 1993). The position of their thumbs and big toes makes it possible to move hand over hand through the trees grasping branches with their feet as well; their fingers and toes act like hooks (Galdikas & Briggs 1999). When they move along the ground, orangutans walk quadrupedally on their fists, not their knuckles as is seen in the other great apes, and they are occasionally seen moving bipedally (Rowe 1996).
Orangutans can live between 50 and 60 years in the wild (Rowe 1996).
RANGE
P. pygmaeus range (in red)
The two species of orangutan are geographically separated and found only on the islands of Borneo and Sumatra. While the whole of Sumatra is part of Indonesia, the island of Borneo is divided into federal states of Malaysia (Sarawak and Sabah) and provinces of Indonesia (Kalimantan), and is partly comprised of the independent sultanate of Brunei (Kaplan & Rogers 1994). Borneo is the third largest island in the world and orangutans occur at low density in all suitable habitat in eight regions of Borneo: Sabah, Kutai region, central Borneo, Bukit Raya/Bukit Baka, Tanjung Puting, Kendawangan, Gunung Palung, and Gunung Nyuit (Rijksen et al. 1995). Orangutans are mainly found in northwestern Sumatra in the Leuser Ecosystem (formerly Gunung Leuser National Park) and the surrounding area, and may be thinly spread down the west coast of the island (van Schaik et al. 1995; Rijksen & Meijaard 1999). Estimates of the orangutan population on Borneo suggest that there are about 55,000 in the wild, while the Sumatran orangutan is thought to number 7,000 individuals (Singleton et al. 2004). There are about 350 orangutans in captivity in the United States (Rijksen & Meijaard 1999).
P. abelii range (in red)
Studies on wild orangutans have been on-going for more than 30 years. One of the most important field sites is Tanjung Puting National Park on Borneo, made famous by Biruté Galdikas who, like Jane Goodall (chimpanzees) and Dian Fossey (gorillas), was sponsored by Louis Leakey, to study wild orangutans in the early 1970s. More than just a field study site, Galdikas established a rehabilitation center and tourist program for the area, bringing international attention to the plight of wild orangutans (Rijksen & Meijaard 1999). Bornean orangutans are also studied at Kutai and Sebangau National Parks and Mawas Reserve in Kalimantan and at Kinibatanga in Sabah (Husson pers. comm). The Leuser Ecosystem on Sumatra has several key study sites including Suaq Balimbing, Renun, and Ketambe, though serious habitat loss has compromised research in these forests (Delgado & van Schaik 2000; Husson pers. comm.). Pioneering ecological and behavioral research on wild orangutans at the Ketambe study site in Gunung Leuser was conducted by H.D. Rijksen.
HABITAT
Bornean orangutans live in isolated fragments of the oldest forests on Earth in a total area of 150,000 km² (57,915 mi²) comprised of hilly or mountainous areas as well as lowland swampy areas (Kaplan & Rogers 1994; Rijksen & Meijaard 1999; Rijksen 2001). The two major types of forest on Borneo are peat swamp forest and lowland dipterocarp forest (Rodman 1988). Dipterocarps are members of a family of trees (Dipterocarpaceae) that characterize this area of the world and are highly valued as timber resources (Kaplan & Rogers 1994). Orangutans utilize primary tropical rain forest and old secondary forest at low elevations, though they may also venture into grasslands, cultivated fields, gardens, young secondary forest, and shallow lakes (Galdikas 1988). Rainfall, averaging 4300 mm (14.1 ft) annually, is relatively uniform across the area and is heavy from December through May as well as in September, while June through August is dry. Temperatures range from 18° C (64.4° F) to 37.5° C (99.5° F) (Galdikas 1988; Knott 1998). Orangutans on Borneo occupy all forested habitat except for northern Sarawak and Brunei and the region east of Sungai Barito and south of Sungai Mahakam. They are also thought to be restricted by elevation and are not found in forests at elevations greater than 1000 m (3281 ft) (Husson pers. comm.).
Sumatran orangutans range across a total area of 26,000 km² (10,039 mi²) comprised of wide plateaus and mountainous regions, at elevations up to 1500 m (4921 ft), as well as lowland swamps at sea level (Rijksen & Meijaard 1999). They are found in lower population densities at higher elevations, and lowland dipterocarp, freshwater, and peat swamp forests are of primary importance. Annual rainfall is about 3000 mm (9.84 ft) with the wet seasons ranging from March to June and September to December. Average annual temperature is 29.2° C (84.5° F) but ranges from 17° C (62.6° F) to 34.2° C (93.5° F) and humidity is near 100 % year-round (Rijksen 1978).
ECOLOGY
Pongo pygmaeus
Orangutans are found in the highest densities in areas which have a mosaic of habitat types that provide high quantities of food throughout the year such as lowland swamp forests, where tree diversity is much higher, than in hilly or mountainous regions (Rodman 1988; Kaplan & Rogers 1994; Russon et al. 2001). Peat swamps support medium-densities of orangutans and they are found in the lowest densities in dipterocarp forests (Husson pers. comm.). They eat a wide variety of plant species but are mainly frugivores 61% of their diet). They have been recorded eating buds, open flowers, young leaves, bark, sap, vines, orchids, reed roots, bird eggs, spider webs, termites, caterpillars, ants, fungi, honey, and other various plant parts (Rijksen 1978; Galdikas 1988). Extreme variability in the abundance of fruit from season to season and year to year is typical of dipterocarp rainforests. Mast fruiting occurs every two to 10 years and is a phenomenon in which large numbers of trees fruit simultaneously despite no seasonal change in temperature or rainfall (Knott 1998). During this time, orangutans engorge themselves with fruit, greatly exceeding their daily caloric intake requirements and putting on additional fat stores. In periods of high fruit abundance, males consume more calories and spend more time feeding per day than females. This propensity to overeat during times of food abundance and efficiency of storing fat reserves may be why captive orangutans often struggle with obesity (Knott 1998). When mast fruiting does not occur during a year, there is still an annual fruit peak. Fruit is widely available during the beginning and end of the rainy season (December and May) and is scarce by the end of the dry season (August) (Galdikas 1988; Knott 1998). Fruit is always preferentially eaten, but when fruits are in short supply, orangutans forage opportunistically and depend more heavily on other plant foods such as bark, pith, leaves, flowers, and insects (Knott 1998). Sumatran orangutans heavily prefer figs over any fruits, especially Ficus species, though figs are largely unavailable to lowland ranging Bornean orangutans (Rijksen 1978; Galdikas 1988).
Orangutans spend more than 95% of their daily activity budgets feeding, resting, and moving between feeding and resting sites (Rodman 1988; 1993). Their daily activity patterns show two peaks, one in the morning and another in late afternoon. After leaving their night nest, orangutans spend two to three hours vigorously feeding in the morning, then rest during the midday hours, travel during the late afternoon, and, in the early evening, prepare their night nests (Rijksen 1978; Galdikas 1988). Day ranges vary between 90 and 3050 m (.056 and 1.90 mi), with an average of 790 m (.491 mi), though males generally travel further than females each day (Galdikas 1988). Day range length is directly proportional to home range size; orangutans with larger home ranges have larger day ranges and those with smaller ones have smaller day ranges (Rodman 1993). In the peat and lowland swamp forests of Borneo, where faunal diversity is great, home ranges for females are between 3.5 and 6 km² (1.35 and 2.32 mi²) (Galdikas 1988). On Sumatra, where orangutans inhabit higher elevations and swamp forests with less diversity, average female home ranges tend to be larger, closer to 8.5 km² (3.28 mi²) Singleton & van Schaik 2001). There is little data on male home ranges because they are likely larger than any study sites, but it is inferred that male home ranges are several times larger than those of females, and as such are neither exclusive nor particularly stable (van Schaik & van Hooff 1996).
Sumatran orangutans are subject to predation by tigers, clouded leopards, hunting dogs, and crocodiles, but tigers constitute the major predatory threat. Clouded leopards are capable of killing Sumatran orangutan adolescents and small adult females, but have not been known to kill adult males (Rijksen 1978). The presence of predators is probably the reason that Sumatran orangutans are rarely seen venturing onto the ground. Bornean orangutans, on the other hand, are not subject to predation by large felids, and are seen more frequently on the ground than the Sumatran species (Rijksen 1978; Galdikas 1988).
Content last modified: June 13, 2005
Written by Kristina Cawthon Lang. Reviewed by Simon Husson.
Cite this page as:
Cawthon Lang KA. 2005 June 13. Primate Factsheets: Orangutan (Pongo) Taxonomy, Morphology, & Ecology .
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