Four days of torrential rain and devastating landslides on Indonesia’s Sumatra island have pushed the critically endangered Tapanuli orangutan closer to extinction, according to a new study.
Researchers revealed that at least 58 Tapanuli orangutans, about seven per cent of the species’ remaining population of fewer than 800, are believed to have died during the extreme weather disaster that struck last November.
The study, published on Wednesday, described the figure as conservative, noting that it did not account for additional threats such as destruction of forest canopies and dwindling food supplies caused by the heavy rainfall.
Cyclone Senyar tore through Sumatra in late November, leaving more than 1,000 people dead in what became Southeast Asia’s deadliest natural disaster of 2025.
According to the researchers, the findings highlight how extreme weather linked to climate change can directly endanger already fragile great ape populations.
While the impact on human communities was immediately evident, scientists said the full scale of destruction to wildlife has been more difficult to determine.
Conservationists had earlier observed a sharp decline in sightings of Tapanuli orangutans after the cyclone, raising fears that many animals had been killed by floods and landslides.
Erik Meijaard, managing director of Borneo Futures in Brunei and one of the authors of the study, had previously told the BBC in December that the cyclone likely killed around 35 orangutans, a loss he described as “a major blow to the population”.
The latest estimate of 58 deaths represents a significant increase from that earlier projection.
In the weeks following the disaster, aid workers discovered the carcass of what was believed to be a Tapanuli orangutan partially buried under mud and fallen logs in Pulo Pakkat village, located in the central Tapanuli district.
“I have seen several dead bodies of humans in the past few days but this was the first dead wildlife,” said Deckey Chandra, a humanitarian worker in the area. “They used to come to this place to eat fruits. But now it seems to have become their graveyard.”
Meijaard confirmed he had viewed photographs of the dead orangutan shared by Chandra.
“What struck me is that all the flesh had been ripped off the face,” he said. “If a few hectares of forest comes down in massive landslides, even powerful orangutans are helpless and just get mangled.”
“It must have been hellish in the forest at the time.”
Researchers said Cyclone Senyar was an unusual event, but stressed that human-driven climate change played a major role in intensifying the disaster.
They warned that extreme rainfall events in the region are expected to become more frequent and severe, posing an even greater threat to the survival of the Tapanuli orangutan and its shrinking habitat.
Previous studies have shown that the species — first identified in 2017, could become extinct if it loses more than one per cent of its population each year.
Indonesia’s government has since suspended major development projects in the Batang Toru forest area of Sumatra, including mining, oil palm and hydropower expansion, allowing researchers more time to assess environmental risks facing the species.
The authors of the report said the destruction caused by Cyclone Senyar demonstrated just how vulnerable the orangutans have become.
“The crisis facing the Tapanuli orangutan illustrates the convergence of climate instability, biodiversity loss, and vulnerability, calling for a coordinated response matching the scale of the threat,” they report wrote.
They added that long-term international backing would be crucial to protecting the remaining population.
“Through strengthened domestic protection, climate-responsive planning, and global financial and technical assistance, we can still prevent the first modern extinction of a great ape species.”
