Scientists say catastrophic floods in Sumatra likely delivered an 'extinction-level' blow to the tapanuli orangutan, the world's rarest great ape. Fewer than 800 tapanulis remain in the wild, and researchers estimate that 6–11% of individuals in the most densely populated West Block may have been killed. Satellite images show large landscape scars and more than 9% of West Block habitat may have been destroyed. Experts urge an immediate halt to damaging development, rapid field surveys, protected-area expansion and forest restoration.
Sumatra Floods an 'Extinction-Level' Threat to Tapanuli Orangutans, Scientists Warn
The Tapanuli region has been devastated by floods that killed nearly 1,000 people (YT Hariono)(YT Hariono/AFP/AFP)
Scientists warn that last month's catastrophic floods in Sumatra represent an 'extinction-level disturbance' for the tapanuli orangutan, the world's rarest great ape. The disaster has caused major habitat loss and threatens the survival prospects of this species, which was only formally classified in 2017.
Scale of the Impact
Tapanuli orangutans are exceptionally rare: fewer than 800 individuals are thought to remain in the wild, confined to a small area of Indonesia's Batang Toru landscape on Sumatra. Conservationists have already reported a suspected tapanuli carcass found in the affected area.
The scientists concentrated their analysis on the so-called West Block, the most densely populated of the three known tapanuli habitats. Before the floods, the West Block was estimated to contain about 581 tapanuli orangutans. Based on satellite imagery and overlap with known ranges, researchers estimate that roughly 6–11% of individuals in the West Block may have been killed.
"The loss of even a single orangutan is a devastating blow to the survival of the species," said Panut Hadisiswoyo, founder and chairman of the Orangutan Information Centre in Indonesia.
"Any kind of adult mortality that exceeds one percent, you're driving the species to extinction, irrespective of how big the population is at the start," warned conservationist Erik Meijaard, underscoring the extreme vulnerability of this small population.
What Satellite Imagery Shows
Remote-sensing analysis reveals massive scars across the mountainous terrain: gashes that in some places extend for more than a kilometre and approach 100 metres wide. The landslides and torrents of mud, trees and water would have swept away vegetation, shelter and food sources — and likely carried off animals in their path.
"I have never seen anything like this before during my 20 years of monitoring deforestation in Indonesia with satellites," said David Gaveau, founder of The Tree Map, after comparing before-and-after imagery.
Contributing Factors and Official Response
Officials and conservationists say deforestation and industrial development in Batang Toru — including plantations, a proposed hydropower project and mining — have increased the region's vulnerability to extreme runoff and landslides. Indonesia's government announced it will suspend operating permits for projects in the area pending review.
A separate study also pointed to climate change — heavier rainfall and warmer seas that can intensify storms — as a contributing factor to the scale of the disaster.
Urgent Conservation Recommendations
The researchers and local experts are calling for immediate action: halt habitat-damaging development, carry out rapid field surveys to assess losses, expand protected areas, and restore lowland forests to provide safer habitat and reduce future risk. They argue these steps are essential to prevent further decline and to give the tapanuli orangutan any realistic chance of recovery.
Panut Hadisiswoyo described the aftermath as eerily quiet, and reiterated: 'This fragile and sensitive habitat in West Block must be fully protected by halting all habitat-damaging development.'
The findings are presented in a draft paper shared with AFP and expected to be released as a pre-print in the coming days. The human toll of the floods — nearly 1,000 people killed in the same disaster — highlights the broader scale of the catastrophe affecting communities and wildlife alike.
