Some researchers believe that the Pongo is too different
morphologically and behaviorally from humans to include it in
Hominidae, and prefer to use Pongidae.
Most orangutan taxonomists now view Bornean and Sumatran orangutans as two distinct species, rather than merely subspecies
of Pongo (Brandon-Jones et al. 2004)
Sumatran and Bornean orangutans show differences in genetic makeup, morphology, ecological adaptations (Groves 2001)(Steiper 2005)
Bornean orangutans are now further divided into 3 distinct subspecies (Singleton et al. 2004)
However some researchers consider the Borneo's and Sumatra's populations as subspecies of Pongo (Courtnay et al. 1998) (Muir et al. 2000)
Common Names: Orangutan, Orang hutan, Mawas,
Looking at distribution of fossil hominids over space and time, researchers Grehan & Schwartz (2009), analyzed physical characteristics of living and fossil hominoids and tested theories of their relatedness:
They conclude that orangutans and humans share a common ancestor that had "established a wide distribution by at least 13 million years ago"
They note that molecular evidence is often cited in support of an alternate concept - that humans and chimpanzees share a common ancestor
In a critique of Grehan & Schwartz (2009) biologists Lehtonen et al. 2011) assert chimpanzees, not orangutans, should still be viewed as sharing a common ancestor with humans:
They compared compared extensive data sets of DNA studies and morphological traits for fossil and living taxa and conclude that chimpanzees are human's' nearest relatives
They acknowledge that there are many similarities between humans and orangutans in life history, physiology, behavior and culture
Recent discovery in northern Thailand of 13 million year old fossil
teeth, very similar to the orangutan
(Chaimanee, et al. 2003)
Orangutans were common throughout mainland and island Southeast Asia 2 million years ago (Delgado & Van Schaik 2000)
The two species of orangutans diverged from one another 2.7-5 million years ago (Steiper 2005)
Most other studies suggest younger dates for the divergence of these two species
DISTRIBUTION & HABITAT
(Delgado & Van Schaik 2000) (Rijksen, and Meijaard, 1999) (Van Schaik et al., 1995)
Orangutan distribution. Black box represents the approximate distribution of the Sumatran orangutan; red box represents the Bornean organutan.
Adapted from www.d-maps.com according to IUCN fact sheets for Pongo abelii and P. pygmaeus
See IUCN pages for detailed distribution.
Distribution spanned across mainland Asia from northern
India, to southern China, Viet Nam, the Malay
peninsula, and Java
Orangutans are the only great apes found today outside of Africa (Delgado & Van Schaik 2000)
Sumatra and Borneo
In Borneo, at least
61 small fragments
In Sumatra, 23 pieces
Reduction of range during the Pleistocene
Most likely due to selective hunting by
prehistoric humans and to changing environmental
Alluvial forest, lowland swamps, and mountain
Up to 200-400 m in elevation
Need an abundance of fleshy
In Borneo orangutans are not found above 500 m; in Sumatra some
populations can be found at 1,000-1,500 m.
Usually found within 10-15 km of water (stream, river, swamp)
Seasonal changes in abundance of orangutans due to heterogeneous
distribution of fruit
(Delgado and van Shaik, 2000) (Groves, 1971) (Utami et al. 2002)
Body Weight: males, 87 kg (191 lbs); females, 37 kg (81.5 lbs) Body Length: males, 970 mm (38 in.); females,
780 mm (30.7 in.) Standing Height: males, 1366 mm (54 in.);
females, 1149 mm (45 in.)
Skin dark gray
Arms about twice as long as trunk
Legs are short, a little more than half the length of the arms
Cheek teeth bunodont (low, rounded)
Long, flowing, reddish pelage
Face of males and females sparsely covered, but may have beard and
HIghly dimorphic; large males may have a body mass more than twice that of females (Delgado & Schaik 2000)
Males that are sexually mature have two distinct body types: one larger and dominant, one smaller but still breeds (Utami et al. 2002)
Hanging throat sac present in both sexes, but much larger in males
Very large cheek pads in males
Males are larger and heavier than females
Males have larger canines and first lower premolars
Males have more pronounced beard and moustache
Little dimorphism is displayed at birth, making sex identification
Sub-specific Differences: May be due to individual rather
than sub specific differences
Bornean orangutans (P. p. pygmaeus)
male facial flanges curved forward
male gular (throat) sacs larger and pendulous
darker color of hair and face
hair shorter and less dense
Sumatran orangutans (P.p. abelii)
male facial flanges lie flat
male gular (throat) sac smaller
lighter color of hair and face
hair longer, thicker, more wooly
BEHAVIOR & ECOLOGY
(Galdikas, 1995) (Kaplan and Rogers, 1994) (Rijksen, 1978) (Rodman, 1977)
(Tuttle, 1986) (Tuttle and Cortright, 1988 )
Bimodal foraging pattern in the morning and afternoon, separated by a
long rest period. Rodman (1977) reported that daily peaks in the Kutai
Reserve, Borneo occurred at 7:00-7:15 AM, and 4:15-4:30 PM. Rijksen
(1978) reported daily peaks in the Ketambe Nature Reserve, Sumatra at
2-3 hours after leaving the nocturnal nest, and at 3:00 PM.
Time spent on daily activities: 43% feeding, 41.5% resting, 13.5%
traveling (often to find food) and 2% other (nest building, mating,
vocalizing, socializing). Actual times vary from place to place and
season to season.
Orangutans sleep at night in arboreal nests that they construct, and
usually move to a new spot every night.
Diurnal resting occurs in arboreal or ground nests, or by leaning on or
draping over large branches. Body posture is upright or supine.
Orangutans were once thought to be solitary. More recent data analysis
suggests that adult males are solitary, while females and young are
Males spend 91% of their time alone; the rest of the time is spent
consorting with a single female, or interacting agonistically with
other males (usually for control of territory or females).
Females spend up to 7 years in continuous contact with each offspring;
often she spends her time with two to three offspring of different
ages; this is the most common social group.
Males do not spend any time caring for young.
Younger orangutans, especially adolescent females, have frequent social
contacts with other immatures and adults
In areas of abundant food, orangutans sometimes congregate to forage.
They arrive independently, or travel in foraging groups.
There is no strict social hierarchy, as seen in other apes.
Social contact appears to be loose and impermanent, and does not form a
Males and females both have large home ranges, which may overlap
Territory of males (500 - 4000 ha) usually larger than territory of
females (64 - 900 ha).
Females have stable home ranges
Adult male home ranges may be stable or transient.
Transient males occasionally challenge resident males for dominance and
control of their territory.
Males are intolerant of other adult males living nearby, but are less
aggressive towards sub adult males.
Once independent, young females set up their own home territory in or
near their mother's. Young males travel much farther away.
Orangutans are generally non aggressive toward humans and each other.
Many individuals reintroduced into the wild after having been in
captivity are aggressive towards humans.
Male-male competition for mates and territory has been observed between
Adult males are more tolerant of sub adult males than of other adult
Play has been observed only rarely in the wild, and usually between
infant and mother.
Intimidation display: males break, shake or drop branches; dive, and
lunge; press lips tightly; gape to expose teeth.
Facial expressions are used to communicate submission, aggression,
fear, and worry.
Gestures between mother and offspring relate to food and affection
Up to 18 different vocalizations have been identified, including 4
types of distress calls made by young animals, 8 types of calls
dealing with threat or fear, and 6 types of calls dealing with mating,
territoriality, play, and contentment.
Males produce a very loud "long call" which attracts estrous
females, and aids in maintaining territorial spacing of males. A
shorter version, the "short call" is often used in reply to
Listen to the "long call,"
courtesy of the BOS-USA
(Balikpapan Orangutan Society), recorded by Soundelux Showorks.
A "kiss-squeak" expresses excitement or fear and is made with
a sharp influx of air through pursed lips.
Information lacking in the literature.
Primarily arboreal, but occasionally travel on the ground
Brachiation occurs over short distances; arms swing over, rather than
Both hands and feet are used in arboreal locomotion
Bipedal locomotion is rare
Quadrupedal locomotion on the ground is somewhat common, but usually
short in duration
Jumping and leaping are uncommon
When coming in visual contact with a snake or large monitor lizard,
orangutans shake tree branches, make kissing vocalizations, throw
twigs, or move away quickly.
Reaction to humans in the wild is usually avoidant. If a human watches
or follows the orangutan persistently, the orangutan often waves,
breaks, and drops branches.
Reaction to other primates feeding nearby is most often passive
Very dexterous, use both hands and feet while gathering food.
Tool use is uncommon and not well developed in the wild; examples
include using leaves as cover when it rains or to wipe their face, and
using sticks to clean their teeth and ears.
Tool use is more common in captivity, and much of it is learned by
imitating their human caretakers.
Many behavioral traits are specific to some populations and
absent in others.
Behaviors are learned from one another, and passed on to
Behaviors are not habitat dependent.
Social groups have a larger behavioral repertoire
than less social populations.
DIET & FEEDING
(Fox et al. 2004)(Kaplan and Rogers, 1994) (Rijksen & Meijaard 1999) (Tuttle, 1986) (Wich et al. 2004)
Diet includes fruits, leaves, bark, nuts, seeds, insects, and honey.
The Sumatran orangutan (P. abelii) is more frugivorous and insectivorous and eats less inner bark of trees than do Bornean orangutans (P. pygmaeus) (Wich et al. 2004
More than 500 plant species recognized in diet of orangs;
They have been described as "gardeners of the forest" for the role in seed distribution(Rijksen & Meijaard 1999)
Eating soil is not uncommon in the wild.
Very rarely observed eating small vertebrates (birds, lizards, rodents,
Time spent foraging on different types of food varies greatly season to
When fruits are scarce, orangutans spend up to 90% of their foraging
time eating shoots and leaves.
Water obtained mostly from the vegetation eaten; also by licking wet
vegetation and fur on forelimbs.
Often exhibit bimodal pattern of foraging (morning and afternoon),
separated by periods of rest.
Time spent foraging each day: 4.3 - 6.3 hours.
REPRODUCTION & DEVELOPMENT
(Benirschke, 2002) (Galdikas, 1981) (Galdikas, 1995) (Kaplan and Rogers, 1994)
(Leighton, et al., 1995) (Nadler, 1988) (Wich et al. 2004)
Orangutan females have a menstrual cycle lasting 22-32 days; a small
amount of bleeding lasts a few days
The menstrual cycle begins at 5-11 years of age; average is 7-8 years.
Females do not exhibit conspicuous genital swellings during ovulation.
Age of first reproduction in females, 12- 15 years. In males, 18-20
Interbirth interval: 7-8 years (Bornean orangutan)
Interbirth interval: 9.3 years (Sumatran orangutan) (Wich et al. 2004)
The longest for any great ape population
In the wild, a female has up to four surviving offspring during her
Forced copulations by sub adult males is used to establish dominance;
pregnancy rarely results.
Cooperative copulations between sub adult males and females has also
Reproduction occurs mainly through sexual contact between fully adult
males and fully adult females.
Sexual contact is often initiated by the female, who tend to choose the
dominant flanged (fully adult) male.
Males may mate
with more than one female (polygyny).
Gestation: 227-301 days
Life Stages: Age ranges for life stages vary by author
Single births most common, occasional twins
Average birth weight, 1.5 to 2.3 kg (3-5 lbs).
Sex ratio at birth 1:1
Infant (0-2.5 years)
Infant mortality is thought to be low.
Infant spends the first 6-8 months firmly attached to the mother, then
begins to spend short periods nearby, but not attached.
Juvenile (2.5 - 7 years)
4-5 years of age: independent of mother, but remain in mother's
Up to 7 years of age: Move out of mother's territory
Weaning takes place as late as 5-8 years of age
Adolescent (7-10 years)
Females: 20-30 kg (44-66 lbs)
Independent of mother
Sexual maturity reached at about 6-8 years of age
Most social age group.
Sub adult Male (10-15 years)
30-50 kg (66-110 lbs)
Sub adult males do not exhibit secondary sexual characteristics typical
of adult male
Development into adult male (accompanied by drastic endocrine changes)
may be repressed as long as the individual lives near a fully adult
male. Once separated, development of secondary sexual characteristics
may occur rapidly.
Delayed maturation of males may be a social strategy used to allow
coexistence of two males
Adult (Female: 8+ years; Males: 15 +
Researchers estimated the age at first reproduction for female Summatran orangutans at 15.4 years (W 2004)
Development of secondary sexual characteristics in males occurs at
15-20 years of age.
Adult females and sub adult males difficult to distinguish unless the
female is accompanied by young.
No evidence of menopause
50-57 years in captivity
45-60 years in the wild
In a study of wild Sumatran orangutans, researchers estimate 58 years for a life span (Wich et al. 2004)
Potential predators: humans, clouded leopard, tiger, possibly the Asian
Compared to mortality figures for other great apes, mortality of all age classes is lower in orangutans.
(Wich et al. 2004)
For infants under one year in age, more than three times lowers than chimpanzees and 2.5 times lower than in gorillas
(Debnar, 2002) (Maple, 1980) (Smits et al., 1995)
Since 1985 there has been a moratorium on inter-breeding the
two subspecies, P.p. pygmaeus and P.p.abelii
due to the possibility that they are separate species.
In captivity, adult male orangutans will often forcibly
copulate with a female, sometimes as often as every day. In
the wild, only sub adult males are occasionally observed to
do this. In the wild males and females live apart except
when a female is in estrous. The pattern of frequent forced
copulation seen in captivity is most likely due to enforced
Although solitary in the wild, orangutans often do better in socialized
groups while in captivity.
Age at first menses and parturition occur much earlier in captivity
than in the wild. 71% of captive females have given birth by age
A captive orangutan ethogram can be found in Maple, 1980.
San Diego Zoological Society
Ken Allen (1971-2000) was a beloved orangutan at the San
Diego zoo, infamous for his many escape attempts. Orangutans
are known for being cunning in captivity. They often observe
human caregivers closely and, when no one is looking,
dismantle parts of their enclosure in order to escape.
January, 2001, Lauran Debnar (Senior Keeper, San Diego Zoo)
began a joint project with the Orangutan Foundation
International to release six captive orangutans back to the
wild, and to assess the viability of old logging concessions
as habitat for rehabilitated orangutans.
Absolutely Apes opened at the San Diego Zoo in the spring of
2003. Orangutans are exhibited together with siamangs, which
coexist with orangutans in the wild, in a naturalistic
CONSERVATION AND POPULATION STATUS
(Delgado & Van Schaik 2000)(Hutchins, et al., 2001) (Rijksen & Meijaard 1999) (Rijksen, 2001) (Singleton et al., 2004) (Singleton et al, 2008)
Between 1996 and 1997 the population dropped by 33% due to fires and drought (Rijksen & Meijaard 1999) (Delgado & Van Schaik 2000)
Estimates obtained between 2000 and 2003 indicate between 45,000 and 69,000 individuals, but rapidly declining since then (Singleton et al. 2004)
Populations on Borneo possibly have "lower mortality, faster breeding, more capacity for rapid population growth" when compared to those of Sumatran orangutans. (Singleton et al. 2004)
Habitats need to support populations of at least 250 individuals to allow genetic stability and stable populations
(Singleton et al.
Rates of hunting over 3% a year will drive any population to extinction, even in good habitats. (Singleton et al. 2004)
Population is much smaller than that in Borneo, approximately 7,300 individuals. (Singleton et al. 2004) (Singleton et al. 2008)
Experienced a population decline of over 80% in the last 75 years (Singleton et al. 2008)
Population in 2000 estimated at 12,500 individuals;
approximately 14% of the estimated population from 1900.
According to the IUCN SSC Conservation Breeding Specialist Group (Singleton et al. 2004) "populations may decline by 50% in about a decade, by 97% in 50 years, and will eventually disappear unless continued habitat loss is stopped"
In 2002 the Nature Conservancy surveyed remote areas of Borneo and
found evidence of approximately 1,000-1250 orangutans, previously
unknown, representing up to 10% of the current orangutan population.