(Borneo) What kind of animal is the orangutan? An updated introduction and explanation of its characteristics, ecology, and habitat.

What kind of animals are Sumatran and Bornean orangutans? We will introduce and explain many of the characteristics, ecology, and habitats of these animals. Orangutans are highly intelligent animals found on the island of Kalimantan (Borneo) in Indonesia. Although they are a familiar animal that everyone knows, they are actually designated as an endangered species.

What is an Orangutan? Basic Stats

Orangutans are animals classified in the Hominidae family, Pongo genus. Their English name is Orang-utan, and their scientific name is Pongo pygmaeus. Males are 100-150cm long, females 80-120cm long, sitting height 70-90cm, and weights are 60-110kg for males and 40-50kg for females. A list of information is below. There is a significant difference in physical size between males and females.

Japanese（和名）	オランウータン
English（英名）	Orang-utan
scientific name(学名)	Pongo pygmaeus
classification（分類）	Mammalia、Primates、Hominidae、Pongo 哺乳綱、霊長目、ヒト科、オランウータン属
IUCN Status(保全状況)	ENDANGERED
Length（体長）	100～150cm
Weight（体重）	40～110kg

About classification

There are the following subspecies of orangutans. Quoted from Wiki.

• Pongo abelii スマトラオランウータン Sumatran orang-utan
• Pongo pygmaeus ボルネオオランウータン Bornean orang-utan
• Pongo tapanuliensis タパヌリオランウータン Tapanuli orangutan

Basic classification

Orangutans are a type of great ape that are closely related to humans within the primate order.

• 界：動物界 Animalia
• 門：脊索動物門 Chordata
• 綱：哺乳綱 Mammalia
• 目：霊長目 Primates
• 科：ヒト科 Hominidae
• 亜科：ヒト亜科 Homininae
• 属：オランウータン属 Pongo

What are the roots and origins of the orangutan?

Orangutans belong to one of the oldest lineages among extant (living) great apes.

The general evolutionary trajectory is as follows:

Early primates
↓
Hominoids (Hominoidea)
↓
Great apes (Hominidae)
↓
Orangutan lineage (Ponginae)
↓
Extant orangutan genus (Pongo)

🌏 Where did they originate?

The lineage leading to modern orangutans is believed to have originated in Asia.

Of particular importance is Sivapithecus, a genus whose fossils have been discovered in the region of India and Pakistan.

Living approximately 12 to 8 million years ago, Sivapithecus is considered highly likely to belong to the lineage closely related to modern orangutans, based on characteristics such as its skull structure.

In short, the history looks like this:

About 10 million years ago
→ Ancestors of the orangutan lineage existed in Asian forests
↓
Lineages subsequently diverged across Asia
↓
Expansion into Southeast Asia, followed by range contraction
↓
Evolution into the modern orangutans of Sumatra and Borneo

🧬 How closely related are they to humans?

Both orangutans and humans are great apes (Hominidae), so they share a common ancestor.

However,

Orangutan
↕
Gorilla
↕
Chimpanzee/Bonobo
↕
Human

…this does not represent a simple linear progression of “Orangutan → Gorilla → Chimpanzee → Human.”

Rather, each group branched off onto a separate evolutionary path from a common ancestor.

🌳 Why did they remain in Southeast Asia?

It is believed that the ancestors of orangutans once inhabited a much wider area of ​​Asia than they do today.

However, climate change and shifts in forest environments caused their habitat to shrink, eventually leaving modern orangutans primarily in:

Borneo

Sumatra The currently known extant species are:

Bornean orangutan

Sumatran orangutan

Tapanuli orangutan

The Tapanuli orangutan, in particular, is a very recently recognized distinct species—officially classified as such in 2017—and inhabits a limited area of ​​Sumatra.

🦧 An interesting fact

The name “orangutan” comes from the Malay and Indonesian phrase orang hutan, meaning “person of the forest.”

And when looking at their evolutionary history, it is a remarkably fitting name.

Habitat

Orangutans are found only in parts of the tropical rainforests of Borneo and Sumatra. During the Pleistocene, they were also found in Southeast Asia and southern China, but are gradually losing their habitat.

1. Overview of Habitat

Orangutans currently only naturally occur on two islands in Southeast Asia:

Borneo

Sumatra

Furthermore, they only live in limited areas of the rainforest, not across the entire island.

2. Habitat by Species
   ① Bornean Orangutan (Pongo pygmaeus)

Habitat

Borneo (
Indonesia (Kalimantan)
Malaysia (Sabah and Sarawak))

Environment

Lowland tropical rainforest

Peat swamp forest

Riverside forest

Characteristics

Prefers low-altitude forests

Most affected by deforestation

② Sumatran Orangutan (Pongo abelii)

Habitat

Northern Sumatra
(Aceh, North Sumatra)

Environment

Tropical rainforests from lowlands to mountains

Can live up to approximately 1,000 meters above sea level

Characteristics

Remains in areas with relatively continuous forests

Prefers fruit-rich forests

③ Tapanuli Orangutan (Pongo tapanuliensis)

Habitat

Tapanuli Region, Southern Sumatra
(Batan Toru Forest)

Environment

Montaneous tropical rainforest (approximately 300-1,300m above sea level)

Steep, inaccessible forest

Characteristics

Very restricted distribution

The great ape with the smallest habitat in the world

3. Habitat commonality

Orangutans are highly adapted to arboreal life.

They spend most of their lives in trees.

Fruit-based diet (durian, fig, etc.)

They build a new “nest” in a tree each night.

Therefore, forest continuity is essential for their survival.

What are its characteristics? What kind of creature is it?

Orangutans are apes, and are the second largest animal after gorillas. Their body hair is quite long, and their whole body is chestnut or reddish brown, with very long hair on their shoulders and back. Their ears are small, their face is black, and their nose is round and protruding along with their mouth. There is hair around their mouth, and they have a throat pouch. Males have a flat protrusion called a “flange.” Their thumbs are short, but they are opposed to the other four, making it easy to grasp things.

1. Physical Characteristics (Appearance)

Long, reddish-brown fur covering the entire body

Extremely long arms (much longer than legs, approximately 1.5 times the body length)

Expressive, human-like eyes

‍ Mature males develop facial flanges (cheek bulges)

⚖️ Weight

Male: Approximately 50-90 kg

Female: Approximately 30-50 kg

Specialized for arboreal life, using their arms to move from branch to branch.

2. Behavioral Characteristics (Lifestyle)
   Spend almost their entire lives in trees

Rarely descend to the ground

Rather than brachiation, they move slowly by grasping branches (prioritizing safety)

️ Build nests every night

Make a new sleeping area every day by combining leaves and branches

Sometimes even build a “roof” to protect from the rain

3. Diet

Mainly eats fruit (60-70%)

Also eats leaves, bark, flowers, and insects

Sustains during times of food scarcity by consuming low-nutrient foods

Memory is important for keeping up with seasonal changes in fruit availability.

What is their personality like?

Orangutans mostly live in trees in forests and other places, and do not come down to the ground. They swing their bodies while hanging from one hand, stretch out their other arm to grab a branch, and move slowly from branch to branch, and usually live alone, but their range of movement is about 2.2 to 6 km2. They also live in groups on rare occasions, so they are very social and intelligent. They cannot swim, but can walk across shallow rivers.

About Intelligence

Orangutans are one of the most intelligent non-human primates. Zoo Atlanta has a touch screen computer where you can see two Sumatran orangutans playing games when they have time. Orangutans can also use sticks and other objects skillfully to make life easier, and it is known that they are quite intelligent.

1. Basic Personality

Gentle and calm

Moves slowly (does not waste energy)

Cautious and observant

Avoids pointless conflicts

Among great apes, they are the quietest.

2. Aggression?

Generally very low

Keeps distance if trouble seems imminent

Choosing to leave rather than threaten

*However,

Mothers protecting their young

Male-male interactions during breeding season

They may become aggressive in exceptional cases.

3. Interpersonal and peer behavior
   Solitary but not lonely

Usually solitary

When encountering other individuals:

Lightly observe the situation

Spending only short periods together

Quietly separate

Not forming groups does not necessarily mean they are unsociable.

4. Curiosity and Intelligence

Very curious

Carefully observe new objects

️ Use tools in an ingenious way

High learning ability (long-term observation of their mother’s behavior)

Not impulsive, but rather thinks before acting.

5. Emotional Expression

Very expressive with expressive facial expressions and gestures

When feeling safe:

Loosen posture

Relaxed with half-closed eyes

Anxious or alert:

Stops movement

Stares intently

Even humans can easily read their emotions.

What is their ecology like?

Orangutans live mainly on fruit, plants, leaves and buds, sap, bark, etc. They reproduce viviparously. They are polygamous and have no set breeding season. The gestation period is 270 days and they can give birth to one baby at a time. Babies are weaned and independent after 2 to 3 years. They change from milk teeth to permanent teeth in about 5 to 8 years, and reach sexual maturity in males at 8 to 15 years and females at 6 to 11 years. They can live for 30 to 50 years in the wild and over 50 years in captivity.

1. Basic Ecology

Mainly arboreal life (rarely descends to the ground)

Primarily solitary

Mainly fruit-eating

️ Extremely slow life rhythm

One of the longest rearing periods among primates

A species that “lives in quiet forests for a long time.”

2. Daily Life Rhythm

Morning

Wakes up from nest (sleeping place)

Slowly moves around searching for fruit

Lunch

Eats → Rests → Moves repeatedly

Often takes a nap during the day

Evening

Builds a new nest during the day

Goes to sleep before sunset

Activity periods are short, with no unnecessary movements.

3. Movement and Home Range

Move using their arms, carefully grasping branches.

Almost no jumping (avoids falling).

Home Range

Males: Wide

Females: Relatively Narrow (Food Resources-Based)

4. Diet and Seasonal Variations
   Staple Food

Fruit (Figs, Durian, etc.)

Supplementary Food

Young Leaves, Bark, Flowers, Insects, Honey

Fruit Scarcity Periods

Sustain Low Nutritional Value Food

Reduced Activity Level (Energy-Saving Lifestyle)

5. Social Structure (Unique)

Does Not Form Groups

Encounters Are Temporary

Mother-Child Relationships are the Core of Society

The “Mother + Child” Unit is the Basic Unit

6. Breeding and Rearing

Gestation Period: Approximately 8.5 months

Birth: One baby per litter

Birth Interval: 7–9 years (one of the longest among mammals)

Baby:

Always stays with their mother until around age 5

Becomes independent after 7–9 years

Learns knowledge (food, movement, and danger avoidance) over time

7. Lifespan

Wild: Approximately 35–45 years

Captive: Can live for over 50 years

Do they have any natural enemies?

Orangutans have no natural predators other than humans, but their babies can be attacked by snakes and other creatures.

About Orangutan Babies

Orangutan babies (babies and young children) are particularly dependent on their mothers,
and have a long learning period, which is one of their most distinctive features among primates.

Let’s explain each developmental stage in an easy-to-understand manner.

1. Immediately After Birth (0-1 Years Old)

Birth Weight: Approximately 1.5-2kg

Short fur, dark face

Clings to mother for most of their life

Cannot move independently

Nutrition is solely through breast milk

Their mother’s arms, belly, and back are their “entire world.”

2. Infancy (1-3 Years Old)

Slowly Becomes Interested in Their Surroundings

Strays from Mother’s Arms and Touches Branches

“Imitates” Food and Puts It to Their Mouth

Still Has Constant Physical Contact

This is the time to learn the basics of the forest through play.

3. Infancy (Ages 3-5)

Move short distances independently

Keep mother in sight

Increase solid food intake, but continue nursing

Observe and imitate nest building

Golden age of observational learning.

4. Juvenile Stage (Ages 5-7)

Nursing is almost complete

Range of activity expands

Learn risk avoidance and food selection through practice

Still sleep in the mother’s nest at night

“Almost independent, but not completely independent.”

5. Independence Stage (Ages 7-9)

Completely separate from the mother

Females tend to remain near the mother’s range

Males travel further

The longest mother-infant relationship among primates.

6. Why do we raise our infants for so long?

A very wide variety of food

Tree-climbing is dangerous

Knowledge and judgment are the difference between life and death

→ This is because “learning” is more important than “instinct” in their ecology.

7. Personality Traits (Young Animals)

Extremely curious

Cuddly

Keen observation skills

Easily returns to mother when startled

More emotionally expressive than adults.

8. Survival Rate and Challenges for Young Animals

If they lose their mother, they are virtually impossible to survive.

Most vulnerable to poaching and deforestation.

In rescue facilities, it can take more than 10 years for them to become independent.

Are orangutans endangered?

Orangutans have lost more than 80% of their forest habitat due to deforestation and development, and their habitat is fragmented. They are currently listed as an endangered species and in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which prohibits unauthorized trade under international law. They are highly protected due to their high risk of extinction in the near future. A 2018 study found that the Bornean orangutan population decreased by 148,500 between 1999 and 2015. They need immediate protection.

1. Conclusion

All three orangutan species are classified as “CR (Critically Endangered)” on the IUCN Red List.

CR (Critically Endangered)
= Imminent extinction in the wild.

2. Status of Each Species
3. Bornean Orangutan

(Pongo pygmaeus)

Estimated population: Approximately 100,000 (but rapidly declining)

Decreased by more than 50% over the past 60 years

Major threats:

Oil palm plantation development

Forest fires

Illegal logging

Large population, but declining very rapidly.

2. Sumatran Orangutan

(Pongo abelii)

Estimated population: Approximately 14,000

Habitat limited to the northern part of the island

Major threats:

Forest fragmentation

Road and plantation development

Small habitat, high risk of rapid decline

③ Tapanuli Orangutan

(Pongo tapanuliensis)

Estimated population: Approximately 800 or less

Habitat: Only one location

Major threats:

Dam construction

Forest fragmentation

The world’s most endangered great ape.

3. Why is it so endangered?

The unique biology of orangutans plays a role.

Their birth intervals are extremely long, at 7-9 years.

They cannot survive if the forest is cut off.

They are learning-dependent, and young cannot survive if they lose their mother.

Once populations decline, recovery is extremely slow.

Can you keep orangutans as pets?

As mentioned above, orangutans are designated as endangered species, so they cannot be kept as pets. There will be information about events at the zoo, so enter the zoo and enjoy watching them. When the zoo opens, go to the general information desk to see the herd exhibit. There are also videos and links on the Internet.

1. Can I legally keep one?

❌ Ordinary people/individuals → Not possible

Orangutans are listed in Appendix I of the Convention on International Trade in Endangered Species (CITES)

IUCN: Critically Endangered (CR)

Trade, import, and personal ownership are strictly prohibited internationally.

Even in Japan, keeping them as pets and personal ownership are not permitted.

2. So why are they in zoos?

⭕ Keeping them is permitted only in limited facilities.

Exceptions are permitted only under the following strict conditions:

️ Zoos and research facilities approved by the national or local government

Breeding and research for the purpose of species conservation

Special permission is required for international movement

The purpose is not “exhibition,” but species conservation.