Sumatran Orangutan

The Sumatran orangutan (Pongo abelii) is one of the two species of orangutans. Found only on the island of Sumatra, in Indonesia, it is rarer than the Bornean orangutan.

 

 

 

 

 

 

 

 

 

 

 

 

 

Physical description

 

The Sumatran orangutan grows to about 1.4 metres (4.6 ft) tall and 90 kilograms (200 lb) in males. Females are smaller, averaging 90 centimetres (3.0 ft) and 45 kilograms (99 lb). Compared to the Bornean species, Sumatran orangutans are thinner and have longer faces; their hair is longer with a paler red color.

Behaviour and ecology

 

Sumatran Orangutan at Bukit Lawang

Compared with the Bornean orangutan, the Sumatran orangutan tends to be more frugivorous and especially insectivorous. Preferred fruits include figs and jackfruits. It will also eat bird eggs and small vertebrates. Sumatran orangutans spend far less time feeding on the inner bark of trees.
Wild Sumatran orangutans in the Suaq Balimbing swamp have been observed using tools. An orangutan will break off a tree branch that is 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 will also use the stick to poke a bee's 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 enjoy eating, 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 quadrumanous locomotion and semibrachiation.

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. 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.
The average interbirth rates for the Sumatran orangutan is 9.3 years – the longest reported among the great apes, including the Bornean orangutan. 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; estimated longevity is more than 50 years. The average of the first reproduction of P. abelii is around 15.4 years old. There is no indication of menopause.

Conservation status

The Sumatran orangutan is endemic to Sumatra island and is particularly restricted to the north of the island. In the wild, Sumatran orangutans survive in the province of Nanggroe Aceh Darussalam (NAD), the northernmost tip of Sumatra. The primate was once more widespread, as they were found more to the south in the 19th century such as in Jambi and Padang. There are small populations in the North Sumatra province along the border with NAD, particularly in the Lake Toba forests. A survey in the Lake Toba region found only two inhabited areas, Bukit Lawang (defined as the animal sanctuary) and Gunung Leuser National Park. The species has been assessed as critically endangered on the IUCN Red List since 2000. It is considered one of "The World's 25 Most Endangered Primates."
A survey in 2004 estimated that around 7,300 Sumatran orangutans still live in the wild. Some of them are being protected in five areas in Gunung Leuser National Park; others live in unprotected areas: northwest and northeast Aceh block, West Batang Toru river, East Sarulla and Sidiangkat. A successful breeding program has been established in Bukit Tiga Puluh National Park in Jambi and Riau provinces.
Nonja, thought to be the world's oldest in captivity or the wild at the time of her death, died at the Miami MetroZoo at the age of 55.

Genomics

 

Orangutans have 48 chromosomes. The Sumatran orangutan genome was sequenced in January 2011, based on a captive female named Susie. Following humans and chimpanzees, the Sumatran Orangutan has become the third extant hominid species to have its genome sequenced.
The researchers also published less complete copies from ten wild orangutans, five from Borneo and five from Sumatra. It was found that genetic diversity was lower in Bornean Orangutans (Pongo pygmaeus) than in Sumatran ones (Pongo abelii), despite the fact that Borneo is home to six or seven times as many orangutans as Sumatra. The comparison has shown that these two species diverged around 400,000 years ago, more recently than was previously thought. It was also found that the orangutan genome has fewer rearrangements than the chimpanzee/human lineage.