Sumatran orangutan

The Sumatran orangutan, known scientifically as Pongo abelii, is one of three distinct orangutan species.

They live exclusively in the northern part of the Indonesian island of Sumatra. These great apes are currently classified as critically endangered. As of 2017, the total population was approximately 13,846 individuals.

Their name comes from the Malay words "orang," meaning person, and "hutan," meaning forest. This translates to "person of the forest." They are rarer than the Bornean orangutan but more common than the Tapanuli orangutan.

Sumatran orangutans are highly intelligent and demonstrate complex tool use.

In the Suaq Balimbing swamp, they have been observed creating specific tools for different tasks. To find termites, an orangutan might break off a foot-long branch. They snap off the twigs and fray the end with their teeth to create a probe. They also use sticks to poke bee nests to reach honey. For the Neesia tree, they use a five-inch stick to strip bark. This allows them to carefully collect painful, fiberglass-like hairs from the fruit. Some individuals even collect entire "toolboxes" of useful sticks for later use.

These apes are primarily arboreal, meaning they live mostly in trees.

Because they are the heaviest mammals to travel through trees, they must manage branch compliance. Compliance refers to how much a branch bends or moves under weight. To stay steady, they use slow movement and long contact times with branches. They also use quadrumanous locomotion and semibrachiation to move through the canopy. They can even sway trees back and forth to lower the energy cost of moving. This lifestyle may be driven by the need to avoid ground predators like the Sumatran tiger.

An orangutan's life consists of five distinct stages.

Infancy lasts from birth to 2.5 years, with weights between 2 and 6 kilograms. During this time, the infant is highly dependent on the mother for food and sleep. Juvenilehood follows from age 2.5 to 5 years. In the adolescent stage, from age 5 to 8, the light patches on their faces disappear. Females become fully developed at age 8. However, males enter sub-adulthood, weighing between 30 and 50 kilograms. They begin to develop cheek flanges, which are large pads on the face.

Finally, males reach full adulthood between 13 and 15 years of age.

Adult males are massive, weighing between 50 and 90 kilograms. This is roughly the weight of a fully grown human.

They possess fully developed cheek callosities and long hair. While females typically live 44 to 53 years in the wild, males live slightly longer. Males can live between 47 and 58 years. Some recorded orangutans have lived much longer in captivity. Puan, at the Perth Zoo, was believed to be 62 years old. Bella, at the Hagenbeck Zoo, is believed to be 61 years old.

Diet plays a major role in their survival and behavior.

They are primarily frugivorous, which means they eat mostly fruit. They prefer fruits with large seeds and fleshy parts, like durians and jackfruit. They are also insectivorous, eating many types of ants and other insects. In the Ketambe area, they have eaten over 92 different kinds of fruit. When fruit is scarce, they may occasionally eat the meat of a slow loris. They even find water in natural tree bowls or from rain caught in their arm hair.

Communication among Sumatran orangutans relies on gestures rather than sound.

Researchers have identified a repertoire of 64 different gestures. About 29 of these have specific, intentional meanings. These include signals to share food, move away, or stop an action. Interestingly, they do not use audible danger signals. Their social structure is also unique. While they form loose clusters around fruit trees, adult males generally avoid one another. This complex social and biological system makes the Sumatran orangutan a vital subject of scientific study.