The Sumatran Orangutan (Pongo abelii) is the rarer of the two species of orangutans. Living and endemic to Sumatra island of Indonesia, they are smaller than the Bornean Orangutan. The Sumatran Orangutan grows to about 4.6 feet tall and 200 pounds in males. Females are smaller, averaging 3 feet and 100 pounds.

Compared to the Bornean Orangutan, the Sumatran Orangutans possess a lighter and longer pelage, a longer face, a smaller stature, and flanges that are covered in small white hairs.

Ecology

Compared to the Bornean Orangutan, the Sumatran Orangutan tends to be more frugivorous and especially insectivorous.^[1] Preferred fruits include figs and jackfruits. It also will eat bird eggs and small vertebrates.^[2] The Sumatran Orangutans spend far less time feeding on the inner bark of trees.

Juvenile Orangutan

Wild Sumatran Orangutans in the Suaq Balimbing swamp have been observed using tools.^[3] An orangutan will break off a tree branch that's about a foot long, snap off the twigs and fray one end. It then will use the stick to dig in tree holes for termites. They'll also use the stick to poke a bees nest wall, move it around and catch the honey. In addition, orangutans use tools to eat fruit. When the fruit of the Neesia tree ripens, its hard, ridged husk softens until it falls open. Inside are seeds that the orangutans love, but they are surrounded by fiberglass-like hairs that are painful if eaten. A Neesia-eating orangutan will select a five-inch stick, strip off its bark, and then carefully collect the hairs with it. Once the fruit is safe, the ape will eat the seeds using the stick or its fingers. Although similar swamps can be found in Borneo, wild Bornean Orangutans have not been seen using these types of tools.

NHNZ filmed the Sumatran Orangutan for its show Wild Asia: In the Realm of the Red Ape; it showed one of them using a simple tool, a twig, to pry food from difficult places. There is also a sequence of an animal using a large leaf as an umbrella in a tropical rainstorm.

The Sumatran Orangutan is also more arboreal than its Bornean cousin; this could be because of the presence of large predators like the Sumatran Tiger. It moves through the trees by brachiation.

Life cycle

The Sumatran Orangutan is more social than its Bornean counterpart. Groups of these orangutans gather to feed on the mass amount of fruiting on the fig trees. However adult males generally avoid contact with other adult males. Rape is common among orangutans. Sub-adult males will try to mate with any female, though they probably mostly fail to impregnate them since mature females are easily capable of fending them off. Mature females prefer to mate with mature males.

Interval birth rates for Sumatran Orangutan were longer than the Bornean ones and are the longest reported interval birth rates among the great apes. Sumatran orangutans give birth when they are about 15 years old. Infant orangutans will stay close to their mother for up to three years. Even after that, the young will still associate with their mother.

Both orangutan species are likely to live several decades; the longevity estimate can span for more than 50 years, with the oldest captive orangutan, Ah Meng, being born in 1960.^[4] Nonja, thought to be the world's oldest in captivity or the wild at the time of its death, died at the Miami MetroZoo at the age of 55.^[5]

The average of the first reproduction of P. abelii is around 12.3 years old with no indication of menopause.^[1]

Orangutan at Schönbrunner Zoo, Vienna, Austria

Status

Sumatran Orangutan at Bukit Lawang

See also

• Fauna of Indonesia

References

External links

• ARKive - images and movies of the Sumatran orang-utan ''(Pongo abelii)''

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