The Sumatran orangutans
The case of the Tapanuli orangutans in Badang Toru
Gunung Leuser Nat Park, Sumatra. Indonesia
The Sumatran orangutans: Guardians of the forest.
The Sumatran orangutan (Pongo abelii) is one of the rarest great apes on Earth, with an estimated population of fewer than 14,000 individuals remaining in the wild.
They survive primarily in the Gunung Leuser ecosystem of northern Sumatra — a dense, mountainous rainforest that tests every step and every breath.
These apes live mostly alone: quiet males, and mothers moving slowly with their children through the canopy. You rarely see them in groups.
Even their presence can feel like a rumor — a slight rustle, a fading branch, a nest tucked high in the leaves.
Their world is subtle, suspended, and green.
Female Sumatran orangutan (Pongo abelii) moving through primary rainforest canopy in Gunung Leuser National Park, northern Sumatra, Indonesia. Natural behavior in wild habitat.
SUMATRAN ORANGUTAN. Female.
Gunung Leseur National Forest.
Sumatra
2024
4K
Reel Duration: 1’50”
Available for licensing.
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Nestled within the Gunung Leuser National Park, a critical refuge for the critically endangered Sumatran orangutans, the Tropical Rainforest Heritage of Sumatra stands as a bastion against extinction. Comprising Bukit Barisan Selatan, Kerinci Seblat, and Gunung Leuser National Parks, this area was honored as a UNESCO World Heritage Site in 2004, only to be declared at risk in 2011 due to relentless environmental threats.
INTRODUCTION – The Team and the Terrain
This encounter didn’t happen by accident. You don’t find orangutans — you’re led to them.
My small team included Toine IJsseldijk,my field companion, who had previously studied at the Ketambe Research Station — a crucial center for orangutan behavior research in northern Sumatra.
His deep experience, both scientific and instinctual, was essential throughout our journey.
Joining us was Haspy Ketambe, a local guide, expert and the founder of Jungle Tours Ketambe, whose intuitive knowledge of Sumatran orangutan movements made all the difference.
Our two porters were the silent backbone of our field effort, carrying equipment through difficult and steep terrain.
And at the heart of it all: “The Professor” Ibrahim Chane — a quiet and highly knowledgeable figure, responsible for monitoring and collecting behavioral data on the orangutans across Gunung Leuser. His work, much of it behind the scenes, was critical in understanding how, when, and where to observe these elusive apes.
Filming in this environment was never easy. Gunung Leuser is steep, wild, and tangled.
And when you’re carrying cameras and tripods — not to mention trying to remain silent and steady — even the smallest movements become a test of endurance.
But it’s worth it, for what you might glimpse.
PART 1 – The Sumatran Orangutans:
The Sumatran orangutans (Pongo abelii) are one of three known species of orangutans, genetically distinct from their Bornean cousins and geographically separated from the Tapanuli population further south.
Today, they survive primarily in the protected forests of Gunung Leuser in northern Sumatra. Critically endangered, they are among the most solitary and arboreal of all great apes.
Unlike many primates, they do not form large groups. Adult males are almost always alone. Females are seen only with their dependent offspring. I never witnessed gatherings or coordinated group activity. It is a quiet, dispersed world.
Their solitude is both a defense and a vulnerability. It keeps them safe from detection — but also makes them harder to find, harder to protect.
This makes filming and observation extremely difficult. You must know what signs to look for: a broken branch, a recent nest, a faint sound. It requires patience, silence, and the guidance of those who have lived among them.
Their quiet way of life is both their defense and their vulnerability.
This solitude makes observation — let alone understanding — far more difficult. But it is also what defines their presence in the forest. They move with calm, unhurried purpose, disappearing just as easily as they appear.
Adult male Sumatran orangutan (Pongo abelii) feeding and moving through forest canopy in Gunung Leuser National Park, Sumatra. Wild natural behavior filmed in primary rainforest habitat.
SUMATRAN ORANGUTAN. Male.
Gunung Leseur National Forest.
Sumatra
2024
4K
Reel Duration: 2’38”
Available for licensing.
SUMATRAN ORANGUTAN.male
Gunung Leseur National Forest.
Sumatra
2024
4K
Reel Duration: 1’41”
Available for licensing.
At the Ketambe science station, for over five decades, researchers like Ibrahim Chane have tracked wild orangutans by foot through some of the harshest terrain imaginable — recording vocalizations, observing maternal bonds, mapping home ranges, and documenting individual lives across generations.
Ibrahin Chane.
Zoologist.
Gunung Leseur National Forest.
Sumatra
2024
4K
Reel Duration: 2’36”
Available for licensing.
Ibrahin Chane. 2
Zoologist.
Gunung Leseur National Forest.
Sumatra
2024
4K
Reel Duration: 2’36”
The differences between Sumatran orangutans & Bornean orangutans
Compared to their Bornean cousins, Sumatran orangutans are:
More slender, with longer facial hair and more expressive, almond-shaped eyes
Lighter in color, with paler, finer hair
More arboreal, spending nearly all their time in the forest canopy and rarely touching the ground.
Tapanulis almost never descend to the forest floor — unlike orangutans in Borneo, which sometimes walk upright between trees. Here, they remain in the trees, avoiding ground predators such as the Sumatran tiger.
By contrast, Bornean orangutans (Pongo pygmaeus) are heavier, with broader faces and darker, thicker hair. Males develop large cheek pads (flanges) as they age, and they are sometimes observed walking upright on the forest floor between trees — something rarely seen among Sumatrans.
Vocalizations also differ: Sumatran orangutans produce higher-pitched, more nuanced calls than the deep, booming long calls of Bornean males.
These differences — in appearance, behavior, and movement — reflect not just genetics, but also adaptation to their unique environments.
Adult male Bornean orangutan (Pongo pygmaeus) in primary rainforest habitat, Kutai National Park, East Kalimantan, Indonesian Borneo.
BORNEAN ORANGUTAN.male
Kutai national Forest
Kaliman tan (Indonesian Borneo)
2022
4K
Reel Duration: 3’03”
Available for licensing.
Diet- A delicate intelligence
The diet of the Sumatran orangutan is vast, intricate, and deeply seasonal.
During our fieldwork in Gunung Leuser, we observed them feeding on wild figs, durian, rambutan, tender shoots, young leaves, flower buds, bark — and occasionally termites or mineral-rich soil. But this is no random foraging. Each choice is part of a mental map, passed through observation and instinct over generations.
According to our field collaborator Ibrahim Chane, orangutans in this region rely on over 40 species of plants for daily nutrition. The diversity of their intake is vital — not just for survival, but for long-term health, mobility, and reproductive cycles.
One quiet morning, after a steep climb, we followed a mother and her child into the high branches of a fruiting ficus. For nearly two hours, she moved slowly, deliberately, choosing the ripest fruit. She knew exactly what she was doing. There was no waste, no doubt — only knowledge.
But this knowledge — and the food sources it depends on — is under threat.
SUMATRAN ORANGUTAN. Female and child.
Gunung Leseur National Forest.
Sumatra
2024
4K
Reel Duration: 2’41”
Threats — A Vanishing Horizon
The Sumatran orangutan (Pongo abelii) is listed as Critically Endangered on the IUCN Red List. Once widespread across the island, its range has now shrunk to just a few protected forest areas — the largest of which is the Gunung Leuser National Park.
Over the past decades, their population has plummeted — primarily due to deforestation, illegal logging, and land conversion. Roads, palm oil plantations, and encroaching farmland continue to eat into what remains of their habitat.
Habitat fragmentation isolates populations, limiting movement and access to food. It also increases the risk of inbreeding and infant mortality — and brings orangutans closer to human settlements, where conflict is inevitable.
Poaching remains a threat, especially targeting mothers whose infants are sold into the illegal pet trade. Even when rescued, few of these young orangutans survive the trauma and separation.
Forest fires — whether accidental or deliberately set for land-clearing — have further degraded key areas of the orangutans’ range. Climate change adds yet another unpredictable layer to their survival.
These apes need time, trees, and space. And all three are vanishing.
PART 2 – The Tapanuli orangutans
Tapanuli orangutan.
Photo: Global Conservation https://globalconservation.org/projects/leuser-ecosystem-sumatra-indonesia
The Tapanuli Orangutans: Earth’s Rarest Great Apes
In 2017, scientists confirmed the existence of a new species of great ape: the Tapanuli orangutan (Pongo tapanuliensis), the most endangered great ape on Earth.
Fewer than 800 individuals remain, surviving in a small and fragmented forest in the Batang Toru ecosystem of North Sumatra, south of Lake Toba.
This discovery was both groundbreaking and heartbreaking.
A new species, found not in some uncharted frontier, but in a region already under threat.
Their forest spans just over 1,000 square kilometers — scattered, steep, and increasingly carved up by development.
Solitary Lives, Hidden Voices
Like their Sumatran and Bornean relatives, Tapanuli orangutans are deeply arboreal and largely solitary. Adult males roam alone. Females stay close to their young. What little we know comes from years of patient observation by local researchers and scientists — often documenting absence as much as presence.
Their long calls — a key trait distinguishing them from other orangutan species — are higher in pitch and composed of more pulses. Their appearance is also distinct: frizzier, lighter-colored hair, flatter faces, and smaller heads than other orangutans.
But they are rarely seen, and even more rarely filmed.
Their lives are lived in the canopy, mostly out of reach — until the forest itself begins to vanish.
The Threats – Fragmentation and the Dam
The greatest threat to the Tapanuli orangutan is not poaching or hunting, but habitat loss — especially from infrastructure and energy development. Roads, mining concessions, agricultural pressure, and illegal logging have already fragmented their range.
At the center of this controversy is the Batang Toru Hydroelectric Dam, a Chinese-funded $1.6 billion project that would cut through key forest corridors. Scientists warn that even small habitat losses in this fragile system can permanently isolate subpopulations — reducing breeding opportunities, genetic diversity, and long-term survival.
In 2021, satellite imagery showed forest clearing within the orangutan’s range. Although dam construction has slowed, conservationists remain deeply concerned. Every road, every trench, every pole pushes this species closer to collapse.
The maps above illustrate the fragmented forest blocks across the Batang Toru ecosystem, the restricted distribution of the Tapanuli orangutan, and the location of the hydropower and mining projects within their habitat.
Map of the Batang Toru ecosystem in North Sumatra, showing the fragmented western, eastern, and southern subpopulations of the Tapanuli orangutan.
Source: IUCN / Erik Meijaard et al., 2019.
Location of the Batang Toru forest in northern Sumatra, Indonesia — the only known habitat of the Tapanuli orangutan.
Source: Mongabay / IUCN.
Map of the Batang Toru Hydroelectric Dam project overlapping Tapanuli orangutan habitat. The infrastructure fragments a critical wildlife corridor.
Source: AsiaNews Network / WALHI.
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Topographic map of the Batang Toru highlands. The Tapanuli orangutans inhabit rugged, montane terrain between 600–1,300 meters above sea level.
Source: Wikimedia Commons / Modified by researchers.
“The Tapanuli Orangutan: Last Refuge Under Siege”
This existential threat has intensified with the proposed expansion of the Martabe gold mine, operated by PT Agincourt Resources (under Jardine Matheson / Astra International). The mine overlaps the only known habitat of the Tapanuli orangutan, including a protected Alliance for Zero Extinction (AZE) Key Biodiversity Area.Mongabay+13Mongabay+13arrctaskforce.org+13
Despite earlier commitments to conservation, recent plans outline the clearing of up to 583 hectares for tailings storage and access roads—expanding into critical orangutan habitat and fragmenting one of the last corridors between isolated subpopulations.Mongabay+1
In 2023, the IUCN SSC’s ARRC Task Force formally criticized the project, citing a lack of transparency, potential bias in the mine’s Biodiversity Advisory Panel, and unchecked environmental impacts beyond permitted zones
The Martabe gold mine’s footprint in Batang Toru, North Sumatra, Indonesia. Image courtesy of Jardines (through Montgabay)
A Narrow Window of Hope
Despite the urgency, there is still time — just barely. Conservation NGOs, local scientists, and international voices continue to advocate for alternatives: rerouted projects, protected corridors, and increased awareness.
The Tapanuli orangutan was discovered too late. But extinction is not inevitable — not yet.
Their highland forest — carved by rivers, fragmented by roads, and increasingly pressured by industrial expansion — is vanishing faster than they can adapt. What remains is a narrow and rapidly closing window of survival.
What happens in Batang Toru will not just define the fate of a species — it will set a precedent for how we treat life on the margins of discovery.
It’s not too late — but only if we choose to act, and to hold those in power accountable while there is still time.
Global Call to Action
The situation has garnered international attention, prompting entities like the Norwegian pension fund to divest from Jardine Matheson over environmental concerns. This global outcry highlights the urgent need for sustained and effective conservation efforts to protect these irreplaceable apes from imminent extinction.
Our documentary aims to shine a light on these charismatic yet critically endangered apes and the relentless pressures they face. It is a call to action, inviting viewers to witness the beauty of Sumatra’s rainforests and the grave threats looming over its inhabitants. For an in-depth exploration of this urgent issue, visit Hans Nicholas Jong’s coverage on Mongabay.
https://news.mongabay.com/2024/03/indonesian-gold-mine-expanding-in-wrong-direction-into-orangutan-habitat/
“The survival of the Tapanuli orangutan depends not just on science and conservation, but on political will, corporate accountability, and global attention.
Without action, we may lose not only a species — but the last echo of a forest never meant to be silent.”
The world is watching, but the clock is ticking.
This program was made in collaboration witth Ketambe Jungle Tours. Ketambe. Sumatra. Indonesia
https://ketambejungletours.com