Extreme rains kill nearly 7% of world's Tapanuli orangutans in Sumatra

An estimated 58 Tapanuli orangutans, representing approximately 7% of the global population, perished during extreme rainfall in Sumatra, Indonesia, last November. This finding comes from a recent study published in the journal Current Biology, highlighting the severe impact of weather events on this critically endangered species.

The Tapanuli orangutan is the rarest of the three orangutan species, with a total population of fewer than 800 individuals. The study indicates that the exceptionally heavy rains in the Batang Toru rainforest region caused widespread landslides. These landslides destroyed about 8,300 hectares of forest, which amounts to nearly 12% of the most important habitat for the Tapanuli orangutan population in the area. Researchers noted that the landslide-affected areas will offer virtually no food for the orangutans for the next five to ten years.

These orangutans exist in only three separate subpopulations within the Batang Toru region. The landslides impacted the largest of these, located in the western part of Batang Toru. Based on satellite imagery and previous population estimates, researchers calculated that approximately 58 individuals lived within the area affected by the landslides, representing about 11% of the western subpopulation.

The study provides the first quantitative evidence that extreme rainfall can pose an immediate threat to the survival of great apes. The losses are particularly devastating for the Tapanuli orangutan due to its slow reproductive rate and small, isolated populations. Previous research has shown that even a 1% annual increase in losses can lead to the species' extinction in the long term. The study's authors attribute the increased probability and intensity of such extreme rainfall events to climate change and are calling for more effective protection of the Batang Toru region to ensure the species' survival.