Orangutan Fact Sheet

Orangutan, Pongo pygmaeus, Pongo abelii
July 2003

Fact Summary
Taxonomy and Nomenclature
Distribution and Habitat
Physical Characteristics
Behavior and Ecology
Diet and Feeding
Reproduction and Development
Diseases and Pathology
Managed Care
Conservation & Population Status
Web Resources
Bibliography

TAXONOMY & NOMENCLATURE
(Brandon-Jones et al. 2004) (Courtney et al. 1998) (Delgado & van Schaik. 2000) (Fleagle, 1999) (Grehan & Schwartz 2009) (Lehtonen et al. 2011) (Muir et al., 1998) (Muir et al. 2000) (Singleton et al. 2004) (Steiper 2005) (Tuttle, 2001) (Warren et al., 2001)
(Wilson & Reeder, 1993) (Xu & Arnason, 1996)

Describer (Date): Linnaeus, 1760 (Simia pygmaeus)

Kingdom: Animalia
    Phylum: Chordata
        Class: Mammalia
             Order: Primates
                    Superfamily: Anthropoidea
                         Family: Hominidae (synonym: Pongidae)
                              Genus: Pongo
                                  Species: P.abelii, Bornean Orangutan
                                  Species: P. pygmaeus, Sumatran Orangutan
                                        Subspecies: Pongo pygmaeus pygmaeus
                                                            Pongo pygmaeus morio
                                                            Pongo pygmaeus wurmbii

Taxonomy and Nomenclature

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, Mawih, Kihau

Evolutionary History

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)
Distribution

Prehistoric distribution:
- Distribution spanned across mainland Asia from northern India, to southern China, Viet Nam, the Malay peninsula, and Java.
Present range:
- Orangutans are the only great apes found today outside of Africa (Delgado & Van Schaik 2000)
- Sumatra and Borneo
- The orangutan's range in Borneo is fragmented into at least 61 pieces, and in Sumatra into 23 pieces
- The reduction in range of the orangutan during the Pleistocene was most likely due to selective hunting by prehistoric humans, and to changing environmental conditions.

Maps: Click on the map icons to see a larger image.

Present (1997) distribution

Habitat

Ideal habitat: alluvial forest, lowland swamps, and mountain foothills; up to 200-400 m in elevation; an abundance of fleshy fruits.
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

PHYSICAL CHARACTERISTICS
(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.)

General

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)

Pelage

Long, flowing, reddish pelage
Face of males and females sparsely covered, but may have beard and moustache.

Sexual Dimorphism

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 difficult

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 )

Activity Cycle

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.

Social Groups

General

Orangutans were once thought to be solitary. More recent data analysis suggests that adult males are solitary, while females and young are more social.
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.

Hierarchy

There is no strict social hierarchy, as seen in other apes.
Social contact appears to be loose and impermanent, and does not form a community structure.

Territorial Behavior

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.

Aggression

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 adults.
Adult males are more tolerant of sub adult males than of other adult males.

Play

Play has been observed only rarely in the wild, and usually between infant and mother.

Communication

Displays

Intimidation display: males break, shake or drop branches; dive, and lunge; press lips tightly; gape to expose teeth.

Visual Signs

Facial expressions are used to communicate submission, aggression, fear, and worry.
Gestures between mother and offspring relate to food and affection

Vocalization

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 other calls.
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.

Olfaction/Scent Marking

Information lacking in the literature.

Locomotion

Primarily arboreal, but occasionally travel on the ground
Brachiation occurs over short distances; arms swing over, rather than under
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

Interspecies Interaction

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

Other Behaviors

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.
Recent behavioral studies suggest that orangutans exhibit primitive culture (van Shaik, 2003)
- Many behavioral traits are specific to some populations and absent in others.
- Behaviors are learned from one another, and passed on to subsequent generations
- 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, slow loris).
Time spent foraging on different types of food varies greatly season to season.
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)

Reproduction

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 years.
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 lifetime.

Courtship

Forced copulations by sub adult males is used to establish dominance; pregnancy rarely results.
Cooperative copulations between sub adult males and females has also been observed.
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

Birth

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 territory
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 + years)

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.

Longevity

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)

Mortality

Potential predators: humans, clouded leopard, tiger, possibly the Asian hunting dog.
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

DISEASES AND PATHOLOGY
(Rijksen, 1978)(Smits, et al., 1995)

Confiscated orangutans in Indonesia have high incidence of disease including tuberculosis, hepatitis A, B, C, and E, cholera, and malaria. Parasites also common.
Rehabilitant orangutans in Sumatra were found to have myiasis (fly maggots) infestations, leeches, intestinal parasites (helminth larvae, nematodes, hookworm), ticks, chiggers, scabies; also upper respiratory diseases such as the cold and flu.
Data on disease and pathology in the wild is limited.

MANAGED CARE
(Debnar, 2002) (Maple, 1980) (Smits et al., 1995) Captive Breeding

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 proximity.
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 12.
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 enclosure.

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)

Population Status

Bornean orangutans:
- 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. 2004)
- Rates of hunting over 3% a year will drive any population to extinction, even in good habitats. (Singleton et al. 2004)
Sumatran Orangutans:
- 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.
ISIS captive population

Conservation

CITES: Appendix I
IUCN - Critically Endangered - Sumatran Orangutan
- Pongo abelii
IUCN:- Endangered : Bornean Orangutan (all three subspecies of Pongo pygmaeus)
- Pongo p. morio
- Pongo p. pygmaeus
- Pongo p. wurmbii

In Indonesia: Protected
Rehabilitation centers have been set up to acclimate once-captive orangutans to life in the wild.
Problems with reintroductions: behavioral problems due to previous association with humans; high incidence of disease.

Threats to survival

Habitat loss and fragmentation in Borneo and Sumtra: logging, clearing for cash crops, human population pressure, fires, drought
- In Sumatra, an estimated 1,000 orangutans were lost because of forest loss each year in the 1990's;
- In Sumatra: new political stability since 2005 has allowed many new logging and palm oil concessions (Singleton 2008)
Hunting by humans for the pet trade and for food
Political unrest, making it difficult to implement conservation strategies
Extremely slow reproductive rate makes the orangutan more vulnerable to long-term disturbance
Orangutans' highly arboreal lifestyle makes them more vulnerable to habitat fragmentation, as they rarely travel long distances on the ground.

Important Web Resources:

Primate Info Net: Website of the National Primate Research Center at the University of Wisconsin.
Orangutan Network: supporting research and conservation of orangutans.
Balikpapan Orangutan Survival Foundation: Indonesian non-profit environmental organization.
Gunung Palung Orangutan Project: fact sheet, flora and fauna list, research, conservation.
Orangutan Foundation International: News, conservation, photographs
Rehabilitation sites -detailed information, sponsored by Dr. A. Russon, York University
Trial by fire: Forest fires and forest policy in Indonesia's era of crisis and reform:PDF formatted paper describing the devastating fires in 1997-1998. Includes very detailed maps showing forest cover, fires and their effects, orangutan distribution, protected areas, and land use.

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