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Wildfire Smoke is Poisoning the Bornean Orangutans

By Natalya Hebert

The devastating effects of wildfires on human civilizations are well-known in the United States, especially with the growing crisis in the California area. This is primarily due to climate change However, the increased rates of wildfires are occuring around the world, and are ravaging not only human societies, but all of the animal communities in the area as well.

One country that has been especially damaged by wildfires is Indonesia, home to the Bornean orangutans. The orangutans live in peatlands, or tropical forests where the soil becomes waterlogged, preventing the decomposition of organic matter. These peatlands act as a natural carbon sink, withdrawing carbon from the atmosphere and into the organic matter the peatlands are composed of, without being released back into the air through decomposition. When the peatlands are drained by humans, however, (usually to make room for agriculture) they create huge expanses of extremely flammable and carbon-rich peat. The flammability is further exacerbated by drought and irregularities in normal weather patterns, and, inevitably, these peatlands go up in flame.

The fires in this area have been raging for decades, with the most severe fires occurring in 1997 and in 2015. Peat fires are the “perfect storm,” according to the researchers. They pollute the air with an abundance of hazardous materials, including carbon dioxide (the gas that is currently damaging the earth’s ozone layer), carbon monoxide (a poisonous gas that reduces oxygen in the brain), and particulate matter (microscopic pieces of matter suspended in the air).

Peatlands are a major ecosystem in Indonesia, and home to the critically endangered Bornean orangutans. Though hundreds of orangutans were killed directly in the 2015 fires, more than 93,000 have unexpectedly died since 1999, indicating that the damage the wildfires are doing to the orangutans’ overall health runs deep.

In this study, Erb et al. (2018) set out to uncover whether the high particulate matter in the air was having an effect on the orangutan’s energy levels. They recorded information on the orangutans’ travel times, travel distances, resting times, and ketones in their urine in three time periods, categorized as pre-smoke, smoke, and after-smoke. After exposure to the harmful wildfire smoke, the orangutans drastically reduced the time they spent traveling, and instead spent more time resting and eating, potentially to preserve their energy.

Orangutan activity and energetics across pre-smoke, smoke, and post-smoke study periods. Adapted from “Graphs of energy and activity levels in Bornean orangutans” by Erb, W. M., Barrow, E. J., Hofner, A. N., Utami-Atmoko, S. S., & Vogel, E. R., 2018, Scientific Reports, 8(1).

After exposure to the smoke, many orangutans fell into a negative energy balance, in which they were spending more energy than they were saving. This dramatic increase in energy expenditure is likely attributed to allostatic load, or the “wear and tear” that occurs on an animal’s body after they are exposed to severe or chronic stress. In this case, the stress on these orangutans was so severe that staying alive required more energy than they were physically able to take in. For the orangutans, the extra energy that they needed was so great that many fell into a state of ketosis, in which the body runs out of carbohydrates to burn and starts breaking down fatty acids for energy. Over prolonged periods, this can be extremely dangerous to an animal’s health (Erb et al., 2018).

The direct effects of wildfires on wildlife are apparent to any observer: Habitats burn, animals are unable to find food, and things die. But the effects go so much deeper. Orangutans that lived in untouched forests, who were still breathing in the toxic smoke, suffered considerable damage to their bodies over the span of two years. For a species whose population is already dwindling, the implications of this study are alarming. As usual, it is up to humans to attempt to reverse some of the suffering that others have caused for animals. As the species with the most power over the planet that we all share, we can’t lose sight of the lives that billions of other animals also lead. This type of study, one that shows that there is a problem in the first place, should be only the beginning. Moving forward, we must recognize animals as living beings too, and consider the snowball effect that occurs when their habitat is drastically altered. From the seemingly harmless act of turning some land into a place to farm, the only life these orangutans ever knew went up in flames.


Erb, W. M., Barrow, E. J., Hofner, A. N., Utami-Atmoko, S. S., & Vogel, E. R. (2018). Wildfire smoke impacts activity and energetics of wild Bornean orangutans. Scientific Reports, 8(1). doi:10.1038/s41598-018-25847-1

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