Some researchers believe that the Pongo is too different
morphologically and behaviorally from humans to include it in
Hominidae, and prefer to retain Pongidae.
Based on recent genetic data, many researchers believe that the
subspecies of orangutan should be elevated to full species status;
still controversial due to a high level of intra-island variation.
Common Names: Orangutan, Orang hutan, Mawas,
Mawih, Kihau
Phylogeny
Of the great apes, orangutans are the least related to humans,
splitting off from the common ancestral group the earliest (10 to 12
million years ago), followed by gorillas, and then finally by
chimpanzees and bonobos.
Sivapithecus most probable ancestor, from late Miocene, Asia.
Theory is controversial; many doubt the relationship due to
differences in skeletal morphology between Pongo and Sivapithecus.
Recent discovery in northern Thailand of 13 million year old fossil
teeth, very similar to the orangutan; adds to the confusion of
orangutan evolution. Lufengpithecus chiangmuanensis could be a
relative or ancestor (Chaimanee, et al. 2003)).
The two subspecies of orangutans diverged from one another 2.3 to 0.5
million years ago.
DISTRIBUTION & HABITAT
(Rijksen, and Meijaard, 1999)(Van Schaik et al., 1995)
Distribution
Prehistoric distribution:
Originated on the Asian mainland approximately 2-3 million
years ago.
Distribution spanned across mainland Asia from northern
India, to southern China, Viet Nam, the Malay
peninsula, and Java.
Present range:
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)
Body Weight: males, 45-100 kg (99-220 lbs); females, 35-50
kg (77-110 lbs) Body Length: (average):males, 956 mm (37 in.); females,
776 mm (30 in.) Standing Height: (average): 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
Very large cheek pads in males
Hanging throat sac present in both sexes, but much larger 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.
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
(Kaplan and Rogers, 1994)(Tuttle, 1986)
Diet includes fruits, leaves, bark, nuts, seeds, insects, and honey.
Preferred food: fruits, especially figs and durian.
Eat up to 100 types of fruit.
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)
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.
In the wild, a female has up to four surviving offspring during her
lifetime.
Menopause occurs at approximately 48 years of age.
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 of a species showing strong sexual dimorphism often defend harems
of females; this is not the case for orangutans, although they do 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)
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
50-57 years in captivity
45-60 years in the wild
Mortality
Potential predators: humans, clouded leopard, tiger, possibly the Asian
hunting dog.
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
(Hutchins, et al., 2001)(Rijksen, 2001)
Population Status
Bornean orangutan population declined from 23,000 to 15,400 between
1995 and 1998; approximately 7% of the estimated population from 1900.
Sumatran orangutan population in 2000 estimated at 12,500 individuals;
approximately 14% of the estimated population from 1900.
It is estimated that orangutan populations have declined as much as 50%
since 1990.
The present orangutan population in the wild is 14,000-25,000.
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.
