Jakarta: Extreme rainfall and landslides triggered by a powerful weather event in Indonesia’s North Sumatra province have wiped out an estimated 7% of the world’s remaining Tapanuli orangutan population, according to a new scientific study.
Researchers, as reported by NDTV, estimate that at least 58 Tapanuli orangutans — considered the world’s rarest great ape species — died after more than 1,000 mm of rain fell over four days in November 2025, causing widespread flooding and landslides across the Batang Toru ecosystem, the species’ only known habitat.
The Tapanuli orangutan population is estimated at around 800 individuals, meaning the deaths represent a significant blow to the critically endangered species. Scientists warned that such losses could have severe long-term consequences for the ape’s survival. Previous studies have suggested that annual losses of even 1% of the population could eventually lead to extinction.
The study, published in the journal Current Biology, found that landslides destroyed approximately 8,300 hectares of primary forest habitat in the Batang Toru region, equivalent to nearly 12% of a key section of the orangutans’ habitat. Researchers said the estimate of 58 deaths is conservative and does not account for additional impacts from damaged forest canopies and reduced food availability.
Professor Serge Wich of Liverpool John Moores University, a co-author of the study, described the losses as “extremely worrying” for the future of the species. He noted that small and fragmented populations are particularly vulnerable to extreme weather events.
The researchers also linked the severity of the rainfall to human-induced climate change, saying warming temperatures likely increased rainfall intensity in the region. They warned that similar extreme weather events are expected to become more frequent, posing an increasing threat to both the orangutans and their habitat.
Lead author Erik Meijaard of Borneo Futures said the heavy rainfall saturated the soil, causing large sections of forested hillsides to collapse in fast-moving landslides. He stressed that such losses are substantial for a species with such a small population and called for urgent conservation measures.
Conservationists have urged the Indonesian government, researchers and environmental groups to work together to address habitat degradation, poaching and other threats facing the species. Recommendations from the study include expanding protected areas and halting activities that further degrade the remaining habitat.
The Tapanuli orangutan was only identified as a distinct species in 2017 and is found exclusively in the Batang Toru forests of North Sumatra, making it one of the most endangered great ape species on Earth.
