Junaidi Hanafiah, Central Tapanuli, Indonesia – Since it was first described by scientists in 2017, the Tapanuli orangutan, one of the world's rarest great apes, was believed to live only in the Batang Toru forest of Indonesia's North Sumatra province. But new findings reveal that the species (Pongo tapanuliensis) also inhabits a peat swamp forest some 32 kilometers (20 miles) away, adding a new layer to the understanding of its range.
On Sept. 26, 2025, a field team from the Sumatran Orangutan Conservation Foundation – Orangutan Information Centre (YOSL-OIC), accompanied by Mongabay Indonesia journalist Junaidi Hanafiah, documented a mother and infant orangutan in the secondary forest of Lumut Maju village in Central Tapanuli district. The observation followed hours of trekking through thick vegetation, and the sighting became the first confirmed record of Tapanuli orangutans in this area, which borders the Indian Ocean.
The location first drew attention in 2022, when local residents reported orangutan sightings to YOSL-OIC's Human-Orangutan Conflict Response Unit (HOCRU). Initial verification found no apes, but did reveal five nests. Later that year, HOCRU and the YOSL-OIC research team returned for further monitoring across the 1,234-hectare (3,049-acre) peat swamp. They found 17 nests, several newly constructed, indicating active use of the forest by orangutans.
"We found new nests that we categorized as class one nests, which we can confirm to have orangutans," Rio Ardi, the research manager at YOSL-OIC, told Mongabay.
This finding possibly extends the known range of the species, previously thought to be limited to the Batang Toru landscape. According to YOSL-OIC, the discovery provides critical information for conservation strategies, highlighting the importance of overlooked peat swamp forests as potential habitats for the critically endangered Tapanuli orangutan.
The Tapanuli orangutan was only described as a new species by scientists in 2017, yet has the oldest evolutionary history of any orangutan species, diverging from their common ancestor about 3.4 million years ago. Genetic exchanges between orangutans in Batang Toru and other orangutan populations, which we know today as Sumatran orangutans (Pongo abelii), stopped 10,000-20,000 years ago, when the forest corridor between them was replaced by farmland, lakes and settlements. This isolation led to the development of unique physical, vocal and behavioral characteristics between the two species.
Tapanuli orangutans' distinguishing traits include flat cheek pads and curly hair, and their penchant for eating uncommon plant species. The Batang Toru population is estimated at around 800 individuals, and the species is classified on the IUCN Red List as critically endangered, making it one of the most threatened great apes in the world.
Between 2023 and 2024, a joint survey by YOSL-OIC and the North Sumatra provincial conservation department, or BKSDA, recorded several orangutans in the peat swamp forest of Lumut Maju. The first face-to-face encounter came in October 2024, when researchers sighted a male orangutan in the area. To confirm whether the Lumut Maju individuals were Tapanuli or Sumatran orangutans, the YOSL-OIC team collected fecal samples in January 2025 and sent them for testing at a lab outside Jakarta.
DNA analysis of the specimens verified that these were indeed Tapanuli orangutans. Further monitoring also found that this cluster may be more widespread than initially assumed. Thermal drone imagery and ground surveys showed signs of movement in nearby forest patches, including protected forest areas.
Analysis of feeding behavior added more clues about how the species has adapted to its surroundings. In the Lumut Maju forest, the orangutans feed primarily on the fruits of trees such as Syzygium muelleri, Tetramerista glabra, Artocarpus elasticus and Campnosperma coriaceum. YOSL-OIC continues to collect data to build a more detailed picture of their diet and habitat use, Rio said.
The team have reported their findings to the relevant authorities, including the Central Tapanuli district government. Conservationists note that the peat swamp forest in Lumut Maju is especially vulnerable to land-use change because of its nonprotected zoning designation, placing this newly confirmed orangutan habitat at considerable risk.
"In 2025 alone, there's been exceptional land clearing of forests, and now the remaining forest is less than 1,000 hectares [2,500 acres]," Rio said. "We're very worried about the fate of the Tapanuli orangutans there. We can't stop land clearing for plantations in [nonprotected] areas."
When Mongabay Indonesia visited Lumut Maju village on Sept. 26, the signs of change in the peat swamp forest were unmistakable. Large portions of the landscape had been cleared, with patches of bare land stretching across what was once dense forest. The roar of heavy machinery echoed through the area, a reminder of how rapidly oil palm plantation expansion is reshaping the orangutan habitat.
The forest has been shrinking as both local communities and palm oil companies clear land for plantations. Residents of Lumut Maju have long known that orangutans live in the surrounding forest, and many said the authorities were already aware of their presence.
"Furthermore, it's rare for people from outside to come to Lumut Maju because it's far away from the subdistrict center. The roads are not good and pass through two oil palm concessions," Aman Rida, a resident of Lumut Maju, told Mongabay.
This growing pressure on the remaining peat swamp underscores the vulnerability of the habitat, which is already outside formal conservation zones. The encroachment adds urgency to ongoing efforts to understand and protect this newly documented home of Tapanuli orangutans.
The discovery of this population of Tapanuli orangutans outside Batang Toru has sparked both optimism and concern among conservationists. The NGO Green Justice Indonesia (GJI) called the finding a rare opportunity to expand understanding of the species' range, but warned it comes with serious challenges, including the nonprotected zoning designation that leaves the forest vulnerable to rapid clearing.
GJI also noted that because the forest isn't connected to Batang Toru, the orangutan population cluster here is effectively isolated. This isolation raises significant concerns about their long-term survival.
Expert assessments suggest that a viable orangutan population requires at least 250 individuals living in a connected natural forest with sufficient food. In Lumut Maju, the number is estimated to be fewer than 100 individuals – far below the threshold for a sustainable population.
Reestablishing a forest corridor between Lumut Maju and Batang Toru is considered impractical, as the landscape is heavily fragmented by plantations and infrastructure. Conservation experts say this makes relocation the most realistic long-term strategy. Moving these orangutans to the larger, protected forest block of Batang Toru could help increase genetic diversity within the species and secure their future, they say.
"However, it must be ensured that Batang Toru still has forest canopy and that conflict between residents and orangutans will not happen," Panut Hadisiswoyo, the GJI director and an orangutan expert, told Mongabay.
Indonesia's National Research and Innovation Agency (BRIN) noted that the breaking up of forest corridors has reduced orangutans' access to natural food sources, forcing them to forage for crops in nearby farms.
In Batang Toru, local communities grow crops like sugar palm, durian, petai, coffee and cinnamon for their livelihoods. Over the years, expanding plantations, mining activities, new roads and settlements have carved up the orangutans' habitat. With their wild fruit trees disappearing, the apes have begun entering community lands in search of food.
BRIN's monitoring shows that over the last four years, several orangutans have been recorded on farmland in villages in the area. Some have even adapted to foraging regularly on farms.
Researchers say this human-orangutan interaction doesn't have to escalate into unmanageable conflict. Sustainable coexistence remains possible if conservation strategies integrate both the ecological needs of the orangutans and the economic realities of local communities, they say. BRIN noted that approaches rooted in local knowledge and ecosystem services could help balance these interests while reducing pressure on the remaining forest.
The North Sumatra provincial government's current zoning plan, which runs to 2037, defines Batang Toru's natural forest zone as spanning nearly 241,000 hectares (596,000 acres), with more than half designated as protected forest and the remainder as buffer zones for production and other land uses. The Tapanuli orangutan faces escalating threats from habitat loss and fragmentation driven by hydropower construction, gold mining, agricultural expansion, small-scale deforestation, settlement encroachment and planned road development.
Researchers see the discovery of a new Tapanuli orangutan home in Lumut Maju as potentially pivotal for conservation efforts. If this group carries unique genetic traits, it could serve as a critical genetic reservoir for the species' long-term survival. The Lumut Maju cluster is now under close scientific study to determine whether it can withstand habitat pressures or must be relocated to a more secure environment.
"Coexistence means peaceful cohabitation between two parties with different interests," Wanda Kuswanda, principal researcher at BRIN, told Mongabay. "Cohabitation will be realized when there is behavioral adjustment between humans and orangutans, resulting in increased animal populations and communities continuing to receive social legitimacy and economic benefits."
[Basten Gokkon, senior staff writer for Indonesia at Mongabay, translated this reporting. Find him on X @bgokkon.]