TAPANULI ORANGUTAN
Pongo tapanuliensis
Distribution and Habitat
2017 will be remembered as the year that shook the world of primatology, when scientists announced the identification of a new and third species of orangutan—the Tapanuli orangutan (Pongo tapanuliensis). It was observed for the first time in 1939 and again in 1997, but it took the work of international teams studying genetics, morphology, and behavior to conclude that, although similar to the Bornean orangutan (Pongo pygmaeus), the Tapanuli orangutan deserved a classification of its own.
Orangutans originally moved from mainland Asia into Sundaland—which is the cluster of islands that include Sumatra and Borneo. Based on genetic studies, it appears a split between the original orangutan populations south of the Toba caldera occurred about 3.4 million years ago, when a group moved north. A second split occurred 600,000 years ago when another group moved to Borneo. Despite those splits, populations continued to interbreed, and it was not until 10,000 to 20,000 years ago that the gene flow between individuals north and south of Lake Toba ended. This may explain why mitochondrial DNA passed down from the mother seems to indicate Tapanuli orangutans are related to the Borneo species, whereas DNA passed from both parents seems to indicate they are closer to the Sumatran species. It turns out that the Tapanuli is the oldest species of the three.
This great ape can only be found in the South Tapanuli region of Sumatra in a small territory covering about 390 sq mi (1,010 sq km), south of Lake Toba. Their native Batang Toru region—referred to as “Harangan Tapanuli” in the Batak language—is the rich landscape of hilly lowland tropical rainforest and mossy mountainous forest, divided by the Sumatran rift valley.
2017 will be remembered as the year that shook the world of primatology, when scientists announced the identification of a new and third species of orangutan—the Tapanuli orangutan (Pongo tapanuliensis). It was observed for the first time in 1939 and again in 1997, but it took the work of international teams studying genetics, morphology, and behavior to conclude that, although similar to the Bornean orangutan (Pongo pygmaeus), the Tapanuli orangutan deserved a classification of its own.
Orangutans originally moved from mainland Asia into Sundaland—which is the cluster of islands that include Sumatra and Borneo. Based on genetic studies, it appears a split between the original orangutan populations south of the Toba caldera occurred about 3.4 million years ago, when a group moved north. A second split occurred 600,000 years ago when another group moved to Borneo. Despite those splits, populations continued to interbreed, and it was not until 10,000 to 20,000 years ago that the gene flow between individuals north and south of Lake Toba ended. This may explain why mitochondrial DNA passed down from the mother seems to indicate Tapanuli orangutans are related to the Borneo species, whereas DNA passed from both parents seems to indicate they are closer to the Sumatran species. It turns out that the Tapanuli is the oldest species of the three.
This great ape can only be found in the South Tapanuli region of Sumatra in a small territory covering about 390 sq mi (1,010 sq km), south of Lake Toba. Their native Batang Toru region—referred to as “Harangan Tapanuli” in the Batak language—is the rich landscape of hilly lowland tropical rainforest and mossy mountainous forest, divided by the Sumatran rift valley.
Tapanuli Orangutan range map courtesy of the IUCN Red List, used with permission
Size, Weight, and Lifespan Both genders have a lanky body with long limbs, but males are larger than females. Males measure 54 in tall (137 cm) and 155–200 pounds (70–90 kg) and females measure 43 in tall (110 cm) and 90–110 pounds (40–50 kg). Their lifespan is approximately 40 years in the wild and 50 in captivity. |
What Does It Mean?Caldera:
A large volcanic crater. Flanges: Thick pads of flesh that frame the face and develop more prominently in dominant male orangutans. Some less dominant males never develop cheek flanges. Mitochondrial DNA: Genetic characteristics passed on by the mother to her offspring. |
Appearance
At first glance, the Tapanuli orangutans appear similar to the other two species, but there are significant skull and dental morphological differences. The head is smaller than that of Sumatran or Bornean orangutans, for instance, the eye sockets are narrower, and so is the mouth. The coat is cinnamon color and is thicker and frizzier than that of the other two species.
Females have a slightly elongated face with a round forehead, and they have a beard.
Unflanged males sport a big mustache and a long beard; flanged males have a saucepan-shaped face with flat fuzzy cheek pouches.
Their strong, long limbs allow them to move easily in the trees but somewhat hinder their movements on the ground. They are extremely precise in their calculations when propelling their bodies through the branches to move in the direction of their choice, using both feet and hands—a locomotion method referred to as quadrumanous clambering.
At first glance, the Tapanuli orangutans appear similar to the other two species, but there are significant skull and dental morphological differences. The head is smaller than that of Sumatran or Bornean orangutans, for instance, the eye sockets are narrower, and so is the mouth. The coat is cinnamon color and is thicker and frizzier than that of the other two species.
Females have a slightly elongated face with a round forehead, and they have a beard.
Unflanged males sport a big mustache and a long beard; flanged males have a saucepan-shaped face with flat fuzzy cheek pouches.
Their strong, long limbs allow them to move easily in the trees but somewhat hinder their movements on the ground. They are extremely precise in their calculations when propelling their bodies through the branches to move in the direction of their choice, using both feet and hands—a locomotion method referred to as quadrumanous clambering.
Male orangutans of each species: 1. Bornean, 2. Sumatran, 3. Tapanuli. Photo credit: Tim Laman/Creative Commons
Diet
The Tapanuli orangutan’s diet is similar to that of other orangutan species—they eat a lot of fruit, leaves, saplings, buds, and small insects; however, this is the only species known to eat pinecones and caterpillars.
Like other orangutan species, they are expert botanists and know how to consume and use plants for their everyday needs.
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Behavior and Lifestyle
Orangutans prefer solitary life to that of large groups. A male may stay with the mother of his offspring but, most of the time, he disappears into the forest once the mating season is over. Daily Life and Group Dynamics
At sunrise, they set out to find food. Males travel alone; females travel with a baby and sometimes an adolescent. After feeding for a few hours, they rest and start again on their quest for sustenance until late afternoon. They then find a tree of their liking and build a nest for the night. Communication
The long high-pitch call of the male Tapanuli orangutan is a mix between the calls that males in Borneo and Sumatra produce. It also lasts longer and is delivered with more pulses at a higher rate. Reproduction and Family
At 15 years of age, females have their first offspring. They prefer the dominant male in their territory to other males. The reproduction cycle is short (30 days; 5 to 8 days of ovulation) and females give birth every 5 to 7 years, so the reproduction rate is very low. This puts the species at an even higher risk of extinction than the Sumatran orangutan, since the current population only counts 800 individuals. Females are most fertile when fruit is abundant, as their bodies require a lot of calories. The gestation period lasts 227 to 270 days, babies weigh about 3 lb (1.3 kg) at birth, and twins are extremely rare. Infants remain dependent for a long time and do not leave the nest until they reach maturity (11 years old for females/ 15 years old for males), at which time adult males wander off into the forest. Females stay a few years longer to acquire the skills they will need as they become mothers. |
Fun FactsOrangutans are the largest tree-dwelling animals on earth. According to an Indonesian folktale, orangutans are so smart, they keep silent in order not be enslaved by humans. Orangutans have fascinated people for many years and this is probably the reason why Edgar Allan Poe decided to make an orangutan the assassin in his short story “The Murders in the Rue Morgue,” published in 1841. |
Female Tapanuli orangutan. Photo credit: Tim Laman/Creative Commons
Ecological Role
Tapanuli orangutans are seed dispersers and play an important role in the health and regeneration of their natural habitat.
The Batang Toru forest, which has already been reduced drastically over the last three decades, is at even more risk if the current population of Tapanuli orangutans becomes extinct; many plant species would disappear with them.
Tapanuli orangutans are seed dispersers and play an important role in the health and regeneration of their natural habitat.
The Batang Toru forest, which has already been reduced drastically over the last three decades, is at even more risk if the current population of Tapanuli orangutans becomes extinct; many plant species would disappear with them.
Conservation Status and Threats
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With a population of only 800 individuals, these orangutans are extremely rare and are considered Critically Endangered by the International Union for the Conservation of Nature, appearing on the Red List of Threatened Species (IUCN, 2017). The species is listed as one of the world’s 25 most endangered primates in the 2018-2020 Primates in Peril report published by the International Union for Conservation of Nature along with the International Primatological Society and Conservation International.
Because most of the lowlands surrounding their habitat have already been converted for agriculture, their survival is even more challenging than that of the Sumatran and Bornean species. Confined to a small geographical area, Tapanuli orangutans are already split into three blocks—East, West, and those in the Sibuali-Buali Nature Reserve. Without access to wild corridors, the current population may not be able to reproduce and maintain the healthy gene pool, crucial to its survival. |
In addition to habitat loss, orangutans are killed as agricultural pests and hunted for the pet trade.
Although protected, this area is threatened by illegal settling of migrants who cut down the trees, but most of all by upcoming plans to open a hydroelectric dam, which would not only damage the forest but fragment it further. The forest is not only the natural habitat of these orangutans, it is also crucial to provide fresh water to the human population in the region and prevent land erosion from massive floods during the rainy season.
Although protected, this area is threatened by illegal settling of migrants who cut down the trees, but most of all by upcoming plans to open a hydroelectric dam, which would not only damage the forest but fragment it further. The forest is not only the natural habitat of these orangutans, it is also crucial to provide fresh water to the human population in the region and prevent land erosion from massive floods during the rainy season.
Conservation Efforts
The non-profit organization PanEco started a Batang Toru Conservation Program in 2006 aiming to protecting the forest against ecologically disastrous projects.
The governor of Sumatra and the local Tapanuli authorities have agreed that the forest should be protected but there are still areas that are not.
The Indonesian government recognizes the importance of forests in regulating climate and set up pilot programs to trade the carbon values of rainforests on the international markets. The revenue generated for the local population should be equivalent to that of palm oil plantations, which are a major threat to that part of the world.
The non-profit organization PanEco started a Batang Toru Conservation Program in 2006 aiming to protecting the forest against ecologically disastrous projects.
The governor of Sumatra and the local Tapanuli authorities have agreed that the forest should be protected but there are still areas that are not.
The Indonesian government recognizes the importance of forests in regulating climate and set up pilot programs to trade the carbon values of rainforests on the international markets. The revenue generated for the local population should be equivalent to that of palm oil plantations, which are a major threat to that part of the world.
References:
- IUCN Red List – iucnredlist.org
- Batangtoru.org website
- Cell.com website and video of Professor Michael Knützen, University of Zurich, Dept of Anthropology
- The Guardian website
- The Atlantic website
Written by Sylvie Abrams, December 2017
