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A total of 767 individuals constituted the entire population of Tapanuli orangutans in 2019, according to an estimation.(Image credit: Nature Picture Library via Alamy)Share this article 0Join the conversationFollow usAdd us as a preferred source on GoogleSubscribe to our newsletter
A solitary cyclone, fueled by climate change, resulted in the demise of 7% of Tapanuli orangutans — the planet’s most endangered great apes — within a mere four days last year, recent research indicates.
The investigation demonstrates that “weather patterns driven by climate change present an immediate, devastating hazard to the world’s most vulnerable great ape species,” as stated by the scientists.
Tapanuli orangutans (Pongo tapanuliensis) inhabit the Batang Toru forest in northern Sumatra, Indonesia. Having been driven close to extinction due to habitat degradation, the species numbered just 767 individuals in 2019, with 581 residing in the forest’s western section.
Then, Cyclone Senyar occurred.
Over a period of four days in November 2025, the uncommon and destructive tropical cyclone triggered torrential rain and severe landslides throughout this western forest region, leading to the deaths of approximately 58 Tapanuli orangutans. These primates perished from drowning, asphyxiation by landslides, or injuries from falling trees, according to the study, which was released on June 10 in the journal Current Biology.
This loss represents 11% of the orangutan population in the west block and approximately 7% of the entire species.
“This is profoundly concerning for the future survival of this ape,” co-author of the study, Serge Wich, a professor of primate biology at Liverpool John Moores University in the U.K., informed The Guardian.
World’s rarest great apes
Tapanuli orangutans were officially recognized as a distinct species, separate from their Bornean (P. pygmaeus) and Sumatran (P. abelii) orangutan relatives, in 2017, making them the most recently identified and rarest of all great ape species.
Orangutans are particularly susceptible to environmental disturbances due to their prolonged reproductive intervals, with approximately six- to nine-year gaps between offspring. They also depend heavily on forest canopy for their survival.
Orangutans’ slow reproductive rates have made it difficult for them to adapt to human-induced habitat destruction.
(Image credit: Nature Picture Library via Alamy)
In the recent analysis, researchers combined pre- and post-cyclone satellite imagery with estimates of orangutan population density to assess the impact of the flooding and landslides on the apes.
Prior to the cyclone, 99.3% of the Batang Toru forest west block was covered by forest. Subsequently, after the storm’s arrival, 21.8 inches (556 millimeters) of rain fell over four days, causing landslides across 20,517 acres (8,303 hectares) of Tapanuli orangutan territory. The researchers identified over 50,000 “scars” resulting from this landslide-induced habitat destruction within the forest landscape.
This loss of habitat was devastating for the orangutans. “Given the high density (>50,000) of sudden, steppe-slope landslides causing canopy collapse and debris flow into drainage networks, and the limited opportunity for arboreal [via trees] escape during rapid slope failure, we consider mortalities by burial, trauma, or subsequent drowning to be likely,” the authors stated in their study.
The long-term consequences of topsoil destruction on the food sources will also negatively affect the surviving orangutans, the authors noted. As topsoil contains dense networks of plant-feeding fungi, it will take time for the fruits and leaves that the orangutans depend on to regenerate.
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World Weather Attribution, a research collective that examines extreme weather phenomena, determined that Cyclone Senyar was intensified by a confluence of human-driven climate change, an oceanic oscillation known as the negative Indian Ocean Dipole, and La Niña, the cooler phase of the El Niño-Southern Oscillation climate pattern.
Climate change is anticipated to increase the frequency and severity of heavy precipitation globally, including in Indonesia. With El Niño now officially present, the climate event is likely to intensify the Pacific hurricane season. This El Niño period is forecasted to “rank among the largest El Niño events in the historical record going back to 1950,” according to NOAA officials in a June 11 update.
“El Niño conditions will add fuel to the fire of a warming world,” stated U.N. Secretary-General António Guterres in a June 2 video address. “The world must perceive it as the critical climate warning that it is.”
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