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Already endangered orangutans now face new threats from wildfires

Borneo’s endangered orangutans are altering their behavior and vocal patterns following peatland wildfires, a groundbreaking study has found.

This research, spearheaded by Wendy Erb, a postdoctoral associate at the Cornell Lab of Ornithology, could pave the way for scientists to assess the health of these wild animals. They would do so without having to confront the hazards associated with studying them amidst wildfires.

These endangered orangutans exhibit significant changes in their movements and calls after the occurrence of fires, a finding that was recently published in the scientific journal, iScience, on June 13.

“The animals move around less to conserve energy,” stated Erb. The orangutans’ vocalizations also change, becoming “deeper, more raspy and shakier,” akin to the cough of a human smoker.

These vocal features indicate inflammation, stress, and disease, similar to symptoms observed in humans and other animals dealing with illnesses like COVID-19.

Surge in wildfires further threaten endangered orangutans

Indonesia, much like other parts of the world, has witnessed a surge in wildfires, a scenario closely tied to climate change. Additionally, these fires correlate with the El Niño cycles, periods of warming in the Pacific Ocean.

Peatland fires, in particular, pose a unique challenge, as they can burn underground for weeks, releasing remarkably high amounts of harmful gases and particulate matter.

Erb, stationed at the Cornell Lab’s K. Lisa Yang Center for Conservation Bioacoustics, led a research team from the Tuanan Orangutan Research Program to investigate the behavior of adult male orangutans in Borneo.

The team discovered that during the fire season, the region recorded its highest levels of particulate matter. The average daily concentrations rose to nearly 12 times the level classified as hazardous to human health by the U.S. Environmental Protection Agency.

Endangered orangutans as an “indicator species”

Critically endangered orangutans are often viewed as “indicator species.” Their health and behavior mirror the state of their environments.

The repeated and lengthy exposure to toxic smoke resulting from the fires could potentially wreak havoc on the health of orangutans, and, by extension, other wildlife.

The study underscores the pressing need to examine the indirect and long-term effects of Indonesia’s peatland fires. This excludes the obvious issues of the immediate destruction of forests and their inhabitants.

Using acoustic methods to monitor species

Erb believes that the findings of this study are instrumental in understanding the health of these endangered species through acoustic methods. She sees tremendous potential in passive acoustic monitoring to gain insight into the wildfire smoke’s impact on global wildlife populations.

“By uncovering the linkages between acoustic, behavioral, and energetic shifts in endangered orangutans, this research can help scientists and wildlife managers safely monitor the health of this critically endangered species using acoustic methods,” Erb stated.

More about endangered orangutans

Orangutans are one of the most interesting species of primates and are native to the islands of Borneo and Sumatra in Southeast Asia. Here’s everything I know about them:


There are three species of orangutans: the Bornean orangutan (Pongo pygmaeus), the Sumatran orangutan (Pongo abelii), and the Tapanuli orangutan (Pongo tapanuliensis). The latter was only recognized as a distinct species in 2017.


Orangutans have a distinctive appearance. They are known for their reddish-brown fur, unlike other great apes. Adult males are larger than females and have large cheek pads, known as flanges.

Arboreal Nature

They are the largest arboreal (tree-living) mammal in the world. Orangutans spend most of their lives in trees and have adapted well to this lifestyle. They have long, strong arms and curved hands and feet, with an opposable thumb and big toe that helps them grasp branches.


Endangered orangutans are omnivores, but their diet mainly consists of fruits (especially durians and lychees), leaves, bark, and insects. They have also been observed using tools to extract seeds from fruit and honey from beehives.


Orangutans are largely solitary animals. Adult males are usually alone, while females are accompanied by their offspring. They are not territorial but adult males will display aggression towards each other.


Endangered orangutans have a long interbirth interval of 7-9 years, which is the longest of any animal on earth. This slow rate of reproduction makes it harder for their populations to recover from declines.


They communicate using a variety of sounds, from roars and growls to “kissing” sounds. The males produce a loud call, known as the “long call”, which can be heard up to a kilometer away and is used to attract females or intimidate rival males.


Orangutans are very intelligent and exhibit a variety of sophisticated behaviors, such as tool use and construction of elaborate sleeping nests in the trees each night. They are capable of learning and mimicking human behaviors.

Conservation Status of Endangered Orangutans

All three species of orangutans are classified as Critically Endangered by the International Union for Conservation of Nature (IUCN). The main threats to their survival are habitat loss due to deforestation for palm oil plantations, illegal pet trade, and hunting.

Lifespan of endangered orangutans

Orangutans can live up to 45 years in the wild and even longer in captivity.

Orangutans are remarkable creatures, and they play a critical role in their ecosystem by dispersing seeds and promoting forest growth. However, they’re under severe threat and need urgent conservation efforts to ensure their survival.

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