Sumatran orangutan

Where are they located?

Historically, Pongo abelii ranged across the entire island of Sumatra and further south into Java. Its habitat has now been reduced to the north of the island, mainly in the provinces of North Sumatra and Aceh.

What is its habitat?

The Sumatran orangutan is almost exclusively arboreal, preferring trees in tropical rainforests. Some adult males travel on the ground, especially the larger ones; however, females virtually never do.

This species prefers lowland valley forests because the variety of food is greater. However, they can also be found at higher altitudes, and some small populations are known to exist above 1,000 meters above sea level.

Male territories overlap with those of several adult females. Females share areas ranging from 500 to 850 hectares, while males dominate a minimum territory of 2,500 hectares.

Are they endangered?

Pongo abelii is considered one of the 25 most endangered primate species in the world. Estimates of the number of orangutans still surviving have decreased dramatically in the last two decades due to habitat loss and fragmentation, despite being protected by law. The hunting of Sumatran orangutans also continues.

Fragmentation

Oil palm plantations, logging, and mining concessions are the main threats. The latest threat is the construction of new roads within the boundaries of Sumatra's last great rainforests. This will fragment the habitat and the orangutan populations that inhabit it into even smaller and potentially unviable units, as they will be left without sufficient resources to survive.

Hunting

They die at the hands of plantation workers when they steal fruit crops in search of enough food to survive.

Furthermore, some people in Indonesia and abroad are still willing to pay high prices for orangutan infants, which has been illegal since 1931. This not only poses a threat to the infants, but their mothers often fight for them to the death. In fact, it is estimated that for every orangutan sold, between six and eight die during capture and transport.

As a result, only seven of the nine existing Sumatran orangutan populations have long-term viability prospects. However, to date, more than 260 individuals have been reintroduced with the aim of establishing new genetically viable and self-sustaining wild populations.

Assessed by the IUCN Red List of Threatened Species as Critically Endangered (2016).

Sumatran orangutan

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Did you know…?

In Malay, 'orang' means 'person' and 'utan' derives from 'hutan', meaning 'forest'. Therefore, orangutan literally means 'person of the forest'.

Orangutans are known for being the best tool-users among animals, including other apes, and also for being the best escape artists.

When on the ground, orangutans walk on all fours, supporting themselves on their palms or fists. Unlike African apes, orangutans are not morphologically adapted for knuckle-walking.

Orangutans have the longest birth intervals among mammals.

Orangutan offspring continue to visit their mother even after 10 years.

Orangutans have a wide range of facial expressions thanks to the great flexibility of their lips.

Orangutan arms extend beyond the length of their bodies.

Orangutan reproduction is more intense in years with abundant fruit harvests.

Frequently asked questions

How do they recognize each other?

Orangutans are often called "red apes" due to their long, shaggy orange hair. Their skin is dark grey. A difference in height can be seen, varying between 1.30 m and 1.80 m, but the main difference is in weight, ranging from 30 to 90 kg. An adult male can weigh three times as much as an adult female.

Orangutans are the largest arboreal animals in the world. As they primarily live high in the trees, they have developed long arms (up to 2.25 m) which help them swing through the forest. Their feet and hands are incredibly dexterous and they have opposable thumbs like us, which makes it easy for them to pick and peel fruit.

Male Development

They are unique among apes in having an unusually long period of male development and two distinct morphs in adult males (flanged and unflanged). As they mature, some males develop fleshy cheek pads and throat pouches, allowing them to produce long calls to attract females. However, in some individuals called sub-adults, cheek flanges and muscle mass are not developed or their full development may be delayed until they are over 30. Their bodies are usually smaller.

It is not fully understood when or why a mature male undergoes the transformation from unflanged to flanged. It has been hypothesized that the presence of a dominant flanged male in an unflanged male's range inhibits his development. Therefore, the unflanged male will not develop his cheek pads or achieve a large size until the dominant flanged male dies, moves away, or is defeated; or until he himself moves away.

How do they behave?

Orangutans (Pongo abelii) are extremely intelligent. They share over 96% of our DNA. In Sumatra, they use small branches to build tools and extract honey and seeds from hard-to-reach places. They learn and teach each other new skills; scientists have even taught them to communicate, for example, through human sign language and the use of touchscreens. Furthermore, they are able to see things from another's perspective, demonstrating empathy.

Sumatran orangutans have closer social bonds than Bornean orangutans. This is attributed to the abundance of fruit on fig trees, where groups of Sumatran orangutans can gather to feed without worrying about the amount of food available. Adult males are generally solitary, while females are accompanied by their offspring.

Grooming as a social interaction is not common among Sumatran orangutans, but playing has been observed in both adults and offspring. Physical contact is not always necessary; sometimes, simple body language is used as a form of play. In addition, they possess unique and diverse cultures. Nest building is an example of this, as each individual has their own way of doing it.

How do they mate?

Male orangutans are ready to mate at around 15 years old, while females reach sexual maturity at an average age of 12 years. Months of increased fruit availability result in higher mating rates. Both males and females mate with multiple partners.

The two distinct adult male morphs (flanged and unflanged) generally employ different reproductive strategies. Flanged males emit loud, resonant long calls, presumably to attract receptive females and to let other males know their location. Matings between females and dominant flanged males are typically cooperative. In contrast, the mating tactic of unflanged males involves harassment of females, as they appear to be less desirable than fully developed males. Females are cornered by unflanged males and forced to mate. As a consequence, females have developed strategies to avoid or reduce harassment, such as forming non-mating groups with adult flanged males or alliances with other females for protection.

Similar species

Until recently, it was believed that there were only two species of orangutans: the Bornean orangutan (Pongo pygmaeus) and the Sumatran orangutan (Pongo abelii). However, in 2017, a team of international scientists described a new species of orangutan found in Indonesia: the Tapanuli orangutan (Pongo tapanuliensis). This species is endemic to the three districts of Tapanuli, in northern Sumatra, and inhabits approximately 1,100 km² of highland forest in the Batang Toru ecosystem. It appears to have remained isolated from all other Sumatran populations for at least 10,000 to 20,000 years. With no more than 800 individuals, the Tapanuli orangutan is the most endangered great ape.

Sumatran orangutans have longer facial hair and stronger social bonds than their Bornean cousins. Additionally, Sumatran orangutans are almost exclusively arboreal, while Bornean orangutans often descend to the ground (especially adult males).

What do they feed on?

Fruit forms the basis of the Sumatran orangutan's diet, with figs being their favorite. However, they also eat young leaves, liana and palm stems, insects (especially ants and termites), and occasionally tree bark. They have been observed eating meat from small vertebrates, although this is rare. They use their teeth to tear and crush food.

Their fluid needs are met by the large amount of fruit they eat, but they also drink from water sources, cupping their hands to collect it.

About their young

The first offspring is usually born when females are 15 years old. Afterwards, they have one offspring every eight or nine years, making them the mammal with the longest birth interval. Gestation lasts approximately eight and a half months, and birth takes place in a newly built nest near the top of a tree. Twins are not common among Sumatran orangutans.

The development of orangutan offspring takes a long time. For the first one to two years of their lives, infants cling to their mothers, traveling together through the trees and sleeping in the same nests. In the following two years, they learn to climb and explore, always under the protection of their mother. When the family welcomes a new infant, the older sibling begins to separate from their mother and sleep in their own nest. However, they visit every few days. Males do not participate in the care of the young.

All of this means that it takes an extremely long time for the population in areas affected by habitat loss to recover.

Do they have predators?

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Communication and the Senses

Their senses of sight, taste, hearing, and touch are quite similar to ours.

To communicate, they make a sound similar to a "kiss squeak", especially when they are anxious or scared. Also when they feel angry, although in that case they add some "grunts".

Flanged males emit what is known as "the long call", a series of exceptionally loud roars followed by a bellow that can be heard up to a distance of approximately 1 km. They use this to attract females and scare away potential rivals. They can also tear down small trees and branches to add a crashing sound.

Orangutan infants usually shriek, bark, and scream.

What is its life expectancy?

The life expectancy of females ranges from 44 to 53 years in the wild. The life expectancy of males is slightly longer, between 47 and 58 years.

What is its global population?

Only around 13,800 individuals remain. Most Sumatran orangutans are found in the Leuser ecosystem (Aceh and North Sumatra provinces).