Critically endangered (P. abelii), Endangered (P. pygmaeus)
Life span: 50 to 60 years (wild)
Total population: 27,000 (wild)
Regions: Indonesia, Malaysia (islands of Borneo and Sumatra)
Gestation: 8.6 months (260 days)
Height: 970 mm (M), 780 mm (F)
Weight: 87 kg (M), 37 kg (F)
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).
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).
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).
CURRENT RANGE MAPS (IUCN REDLIST):Pongo abelii
| Pongo pygmaeus
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).
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.
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
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 . <http://pin.primate.wisc.edu/factsheets/entry/orangutan/taxon>. Accessed 2014 October 1.