Orangutans share many features with African great
apes, including large body, no tail, building nests for sleeping,
and long, slow lives. Their most distinctive feature is
their red-orange color—other great apes are black. read more…
most impressive feature is extremely large size—they are
megafauna, scientifically, and the world's largest primarily
arboreal mammals. Largest by far are adult males, up to
1.25 m tall and over 100 kg in weight. Their strength is
legendary, reputedly seven times as great as a man's.
Orangutans have opposable thumbs on hands and feet
to facilitate travel in the trees, like all nonhuman primates.
Their arms are unusually long relative to their legs because,
as apes, their main mode of travel is suspensory.
They hang or swing under branches rather than walk on
top as monkeys do. For the same reason they have elongated,
hook-like hands and feet and especially mobile hip
joints. On the ground they mostly walk quadrupedally, on
their fists, but occasionally bipedally like humans.
Adult male and female orangutans are physically very
different (sexual dimorphism). Males are almost twice as
large; they also have flanges on the sides of their face
(cheekpads), long shaggy hair that can resemble dreadlocks,
drooping throat pouches, and a unique long call.
Borneans and Sumatrans also differ. Borneans have
stocky bodies, broad faces, coarse hair ranging from orange
to brown or maroon, and dark skin. Sumatrans are more gracile. They have more slender bodies, narrower
faces, redder, lighter, longer, denser hair, and very light
hair around eyes, mouth, and flanges. Bornean adult
males have larger throat pouches and flanges. Sumatran
males and females both grow long beards and the males
may have mustaches. Origins cannot by identified by looks alone. On Sumatra,
hair grades from bright red to rather dark brown and
individuals with very long, gracile fingers are found along
with those with much stubbier fingers. Variation is even
greater in Borneo, much of it following the geographic lines
that divide its three subspecies.
Life History and Development
Orangutans live life in the slow lane. They grow and
breed slower than any other land mammal, even elephants, and whales. read more…
♦ Life span: 45-55 yr (over 60 in captivity)
♦ Weight: adult M/F 87/37 kg; newborn 1-2 kg
♦ First Birth: 11-15 yr (females)
♦ Gestation: 8.6 mo (260 days)
♦ Inter-birth: 6-9 yr (longer on Sumatra)
♦ Weaning age: 5-6 yr (Borneo), 6-7 yr (Sumatra)
♦ Dependency: 7-10 yr
♦ Dispersal: M and F leave mother's range
Orangutans develop in 5 stages: infant (0-4/5 yr), juvenile (4/5-7/8), adolescent (7/8-15), adult-reproductive (15-
48), post-reproductive (48+). Their development seems
very flexible, accelerating or slowing markedly depending
on food or social conditions. Like other great apes,
orangutans remain semi-dependent immatures for a
greater portion of their lives than other mammals, even
other primates. Infants depend entirely on their mother
until about 2 yrs old and heavily until weaned at 4 or 5.
After weaning, as juveniles, they begin exploring and refining
the basic skills—foraging, nesting, navigating—they
learned as infants. Initially they stay within sight of mother. They only become fully independent as adolescents. Males show a unique bimaturism. Adult males have
two physical types, flanged and unflanged. Unflanged males, usually younger, are mature but have not yet developed flanges, drooping throat pouch, huge size,
and long call. When they do mature it is fast, although
their early long calls often sound rather awkward.
Orangutans are frugivores, or fruit eaters. 50-60% of their foods are fruits. Fruits are poor in proteins and fats,
so they eat many other items too: leaves, flowers, honey,
shoots, stems, seeds, fungus, pith, bark, soil, insects,
eggs, and small mammals. They eat lower quality items
as when fruit is scarce. Some of their foods
are medicinal: they protect against malaria, control parasites,
or treat diarrhea. Orangutans also use leafs as topical medicines; they rub special leaves on their skin to soothe sore muscles and joints.
Distribution and Habitat
In Sumatra, orangutans remain only in the northern
tip. They are found across Borneo, but not everywhere.
Orangutans live in tropical rainforests, mostly lowland and swamp forests rich in biodiversity. read more…
do not produce enough food to support them
permanently. Forests are more productive in Sumatra than Borneo, which is probably why orangutans live at
higher densities in Sumatra. Within their habitat, each
independent orangutan lives within its own home range, an
area it uses regularly. Neighbors' home ranges overlap.
Range size depends on food so they are larger in poor
habitat. An adult female may need a range up to 6-8 km2.
A typical orangutan day starts at dawn around 6:00 am,
waking in the nest where they slept the
night. Then they eat, rest, travel, and (rarely) socialize. read more…
They spend 2-3 hr seriously feeding in the morning, rest
midday, then travel and feed again through the afternoon.
Only about 5% of their day is spent socializing,
probably less avoiding predators (they have few: tigers,
e.g., in Sumatra but not Borneo). They end the day at
dusk, about 6:00 pm, building a new nest for the night.
Foraging. Orangutans spend 50%-60% of their day
foraging. Basically, they follow their foods. They seek
out fruits (their favorite) but are also rather opportunistic,
eating whatever they find along the way. They seem to
remember the location of important foods because they
travel directly to them.
Travel. Each day orangutans travel, at ca 0.3 km/hr,
mostly looking for food within their home range. They
may travel only as far as needed to eat, as little as 90 m
or as much as 3 km. They are rather nomadic, traveling
and nesting in different places each day. They travel
mainly in the trees but adult males may travel on the
ground—perhaps where they are too heavy to move
safely in the canopy. Unlike other apes, orangutans
rarely jump, drop, or brachiate (swing branch to branch
by their arms). Instead they climb, clamber, or sway
slender trees to cross forest gaps.
Resting. Orangutans rest a lot. Each night, they
build an intricately woven nest of leafy branches in the
trees. They often nest near a food tree that can provide
the evening's dinner and tomorrow's breakfast. They
also spend up to 40% of the day resting, napping on a
quickly made day nest or a comfortable branch or liana.
Orangutans are known as quiet, but they communicate
desires, needs, and intentions by vocalizations, gestures,
postures, and facial expressions. read more…
Like chimpanzees and
humans, orangutans peer at items that interest them and
beg for ones they want. They make play faces and
breathy laughter when playful; whimper, pout and throw
tantrums when unhappy, and scream in fear, frustration, or
rage. When someone doesn't understand what they are trying to say, they will try new ways of communicating, sometimes by pantomiming what they want. They apologize after conflicts by being very nice. With partners they like, they even share food. Orangutans also have unique ways of communicating.
They kiss-squeak when annoyed by sucking air through
pouted-pursed lips. As annoyance grows, they make pig
grunts, grumphs, gorkums, and lorks—increasingly intense
throaty, belch-like growls. Adult males long-call and snagcrash
to announce their presence or intimidate. Long calls
start with grumbles then pulses and end with bubbles and
sighs. Snag-crashing is pushing over standing dead trees.
Orangutans are semi-solitary—or semi-social. It is
adults who prefer solitude, especially adult males. Adult
males range alone and are so intolerant of one another
that they may fight to the death if they meet. Adult females
are semi-social, usually living with one or more offspring.
Offspring leave their mother at adolescence but females
stay near their mother's range while males move farther
away. Immatures are more sociable, traveling and playing
with family or friends for days on end. read more…
Orangutans, like other great apes, are the most intelligent
nonhuman primates and the nonhuman species most
similar, mentally, to humans. read more…
In captivity they are famous as the mechanical geniuses of the great apes
for their tool abilities, a hallmark of high intelligence. They
also seem to solve some problems by insight, i.e., thinking
vs. trial-and-error, can master simple sign language
and arithmetic, and can recognize themselves in mirrors.
Wild orangutans use tools less than chimpanzees but
their manual skills are just as complex. They also show
high intelligence in forest travel, possibly having mental
maps of the location of food sources and the distances,
routes, and obstacles in between. They seem to plan
routes in advance, choosing directions that lead to predictable
goals. For such large-bodied beings, just traveling
in the trees probably involves complex calculations to
select what set of branches can support their travel.
Orangutans show high social intelligence despite their
solitary side. Their deception is as sophisticated as chimpanzees'.
They intervene in quarrels to support friends,
console victims of attacks, reconcile after conflicts, and
share food with friends. They are astute social learners,
learning new skills by imitation. They rarely teach but
show others what they want by miming. They may mime
their partner's role as well as their own role—especially if
the partner doesn't respond as they desire. Perhaps the
most stunning finding is that they create complex cultures.
On IUCN's Red List of Threatened Species Borneans
are endangered, at very high risk of extinction in the near
future. Sumatrans are critically endangered, among the
world's 25 most endangered primates. Humans cause
their greatest threats: habitat loss, hunting and disease.
Clearing forests is often the first phase of development.
It destroys orangutan habitat because the forests
humans want are often those orangutans need. Logging,
oil palm plantations and natural resource industries have
cleared vast tracts of Bornean and Sumatran forest.
Development is also at the root of fires that have eradicated
much forest, even if natural droughts set the stage.
Humans hunt orangutans for food, as pests and to
sell to the illegal wildlife trade. Development enables
hunting by making forest foods scarce. Orangutans leave
the forest seeking food, often raid farms or plantations,
and become easy targets. Development also increases
disease threats. Orangutans are susceptible to many
human diseases, even tuberculosis, polio, and hepatitis.