The Tapanuli species is considered one of the rarest great apes in the world, with the less-than 800 remaining apes located in the region of Batang Toru, North Sumatra, south of Lake Toba. - Creative Commons/Tim Laman
MEDAN: For the first time, scientists have confirmed the presence of the critically endangered Tapanuli orangutan (Pongo tapanuliensis), the world’s rarest great ape, outside its only previously known habitat in the Batang Toru ecosystem in North Sumatra.
A research team from the Orangutan Information Centre (OIC) recently identified several Tapanuli orangutans in a peat forest near Lumut Maju Village, Central Tapanuli, approximately 32km north of the Batang Toru ecosystem.
According to Onrizal, an associate professor of ecology and conservation of tropical forests at North Sumatra University (USU), the finding represents a major milestone in efforts to protect the critically endangered species.
For years, researchers have been searching for evidence of Tapanuli orangutans in forests across North Sumatra, beyond the Batang Toru ecosystem.
“This is the first time researchers have managed to find them beyond their known habitat. It also supports predictions made in a 2021 scientific publication, which suggested that the Lumut area could serve as a potential habitat for the species,” Onrizal said on Monday.
Onrizal added that the Lumut peat forest, where the Tapanuli orangutan was discovered, was once connected to the larger Batang Toru ecosystem. However, agricultural expansion and the spread of human settlements have long isolated the area from Batang Toru.
Syafrizaldi, executive director of the OIC, explained that scientists began investigating the Lumut peat forest as a potential Tapanuli orangutan habitat in May 2022, following reports from local villagers who claimed to have seen orangutans in the area.
The Lumut peat forest is officially categorised by the government as an “area for other uses” (APL), which is land designated for non-forestry activities such as development, housing, agriculture, plantations and investment.
“Following these reports, our team conducted a field study in the forest and found five orangutan nests. Five months later, we discovered another 17 nests,” Syafrizaldi said.
He added that between 2023 and 2024, teams from OIC and the North Sumatra Natural Resources Conservation Agency (BKSDA) conducted multiple surveys in the Lumut peat forest.
In October 2024, they finally observed several individual orangutans directly.
To confirm the species identity, the team collected faecal samples for genetic testing in Bogor in January 2025.
The results, released recently, confirmed that the individuals were indeed Tapanuli orangutans, showing the same DNA sequences previously identified in the Batang Toru population.
“An official report on the findings will be released soon by the North Sumatra BKSDA,” Syafrizaldi added.
Based on nest counts, researchers estimate that just six to nine Tapanuli orangutans inhabit the Lumut Forest.
The Tapanuli orangutan, the most recently identified species of great ape, was first discovered in the Batang Toru ecosystem in 1997. However, it was not officially recognised as a distinct species until 2017.
Fossil evidence and genomic studies indicate that the Tapanuli orangutan lineage diverged from other orangutans around 3.38 million years ago, making it the oldest of the three known species.
Scientists believe these orangutans may descend from early populations that migrated from mainland Asia to the Indonesian archipelago over three million years ago.
Compared to their Bornean and Sumatran relatives, Tapanuli orangutans have smaller skulls but larger canines.
Today, the Tapanuli orangutan is confined to the Batang Toru ecosystem, a largely pristine forest spanning roughly 133,841 hectares across the regencies of South, North, and Central Tapanuli.
The total population is estimated at fewer than 800 individuals, making it the rarest great ape species in the world, according to the International Union for Conservation of Nature (IUCN).
Conservationists warn that the species faces a critical risk of extinction due to habitat loss driven by human activity within Batang Toru. Since 2001, around 3,600 ha of its 105,000-ha habitat have been damaged.
The construction of the Batang Toru hydropower plant has further intensified threats to the Tapanuli orangutan.
Environmentalists warn that the dam could fragment the forest, isolating orangutan groups and pushing the species closer to extinction. Habitat fragmentation would limit their access to food and increase the risk of inbreeding, making the population more vulnerable to disease.
The Batang Toru ecosystem is also home to six other large primate species, including siamang, gibbons, lutungs, slow lorises, pig-tailed macaques and long-tailed macaques.
In addition, the forest shelters three critically endangered mammals, the Tapanuli orangutan, Sumatran tiger and pangolin, along with 15 other mammal species, such as sun bears, tapirs and golden cats, all of which are classified as threatened or vulnerable. - The Jakarta Post/ANN
