Wild mammals
Wildfires in Borneo cause long-term harm to orangutans
Long-term monitoring shows forest fires trigger food shortages, health declines, and social breakdown among wild orangutans.
Reported by Phys.org · · 2 min read
Severe drought driven by El Niño has triggered major wildfires across Indonesia, causing peatlands in West, Central, and South Kalimantan to smolder and cover parts of Borneo in thick smoke. While the immediate flames pose an obvious hazard, research shows that these forest fires inflict long-lasting harm on wild orangutan populations long after the smoke clears.
Lingering effects of past blazes
At the Tuanan Orangutan Research Station, where scientists have monitored wild orangutans since 2003, researchers documented severe lingering effects following blazes in 2015. During that emergency, smoke shrouded the study area for 95 days. Primates showed signs of respiratory distress, including coughing, while staying lower in the forest canopy and spending significantly more time at rest.
The 2015 fires destroyed about 15 percent of the Tuanan forest, which led to a fruit shortage that lasted for two and a half years. Scientists believe the extended lack of fruit resulted from smoke blocking sunlight needed for photosynthesis, along with potential losses of pollinating insects.
Faced with scarce preferred foods, female orangutans adapted by minimizing travel, resting more, and feeding on inferior fallback foods. Studies indicated that the animals were forced to break down their own body tissue for energy, resulting in a decline in muscle and tissue mass.
Stress on social structure and breeding
The reduction of suitable forest also forced displaced primates into remaining habitats, causing overcrowding. Increased competition for limited resources strained social ties. Unrelated females displayed higher levels of aggression, while adult females spent less time feeding alongside relatives or their own offspring.
Reproduction halted entirely, with no pregnancies documented among the observed females for two and a half years following the 2015 fires. Furthermore, three of the site's oldest female orangutans vanished by late 2017, a loss far exceeding typical mortality rates for the species.
Recent fires have already destroyed an estimated 30 percent of the Tuanan research area. Experts, including Max Planck research fellow Maria van Noordwijk and institute director Meg Crofoot, note that long-term study sites are vital for tracking how heavily these recurring fires impact orangutans and how long the species will need to recover.
