Is the Smoke from Wildfires Dangerous to Birds?

Smoke can be hazardous to birds just as it is to people, due to the mix of fine particulate matter and volatile chemicals produced during burning. This threat is partially offset by birds’ exceptional mobility and the large volume of air in the atmosphere.

Scientists have only fairly recently begun studying smoke’s effects on birds, as wildfires have become more frequent and larger as a result of climate change. They’ve identified both physiological and behavioral effects of wildfire smoke (see Sources). These are some of the key findings so far:

What Makes Wildfire Smoke Dangerous?

• Smoke can contain dangerous levels of fine particulate matter (particles smaller than 2.5 microns, often abbreviated PM2.5).
• Smoke can contain a mix of volatile organic compounds, carbon monoxide, hydrogen cyanide, nitrogen oxides, ozone, sulfur dioxide, acrolein, benzene, formaldehyde, and heavy metals (Sanderfoot 2021). The actual composition of wildfire smoke depends on what kinds of plants have burned and in what manner they burned (e.g., temperature, duration). 
• Smoke inhalation can damage lung tissue and weaken immune responses. It can also cause carbon monoxide poisoning, neurological impairment, oxidative stress, lung and heart disease, and pulmonary edema (Sanderfoot 2017).
• Because long-burning wildfires create so much smoke, the area affected by smoke extends far beyond the wildfire boundary. For example, during the major fire year of 2020, ground-level smoke from fires in the Pacific Northwest covered an area 27 times greater than the wildfires themselves (Overton 2021).

How Do Birds Respond to Wildfire Smoke?

Birds have a much different respiratory system than humans and other mammals. It is highly efficient at directing air through the lungs to extract oxygen, but this efficiency also renders birds more sensitive to pollutants in the air they breathe.

Fortunately, birds are very mobile and can adjust their behavior to avoid or reduce the effects of smoke (although these adjustments can incur their own costs). A few studies have documented some of these changes in behavior.

Changes to Migration

Migrating birds may adjust their routes/timing to avoid smoke. In September 2020, scientists were tracking four Greater White-fronted Geese during a period of very large wildfires (totaling more than 20,000 square km) and widespread smoke in the Pacific Northwest (Overton 2021). Adjustments the geese made included:  

• Stop and wait: three of the geese paused migration to wait for conditions to improve. They rafted on the Pacific Ocean off Washington for up to 3 days before continuing inland.
• Fly over the smoke: three of the geese also ascended to very high altitudes (4,000 m or 13,100 feet) to fly above the densest smoke.
• Fly around the smoke: one goose diverted course and followed prevailing winds to get out of the smoke, ending up more than 200 miles east of the typical migration route.

These efforts were successful—all four geese reached their typical wintering area in Summer Lake, Oregon. But the adjustments meant that they doubled their time spent on migration. Scientists later calculated that the extra energy the geese expended would have required extra foraging over the next 40+ days to recoup. 

Changes in Behavior and Body Condition

Apart from directly affecting birds’ health, smoke can also alter their behavior with resulting changes to body condition. Research from a long-term banding station in San Jose, California, identified both short-term (acute) and long-term (chronic) effects of wildfire smoke: 

• The study compared 22 years of banding records (for 21 bird species) with data on wildfire smoke. Researchers designated smoky days using the same threshold as the EPA uses for humans: 35 micrograms of fine particulate matter (PM2.5, or particulates smaller than 2.5 microns) per cubic meter.
• Movement: Over the short term, smoky conditions resulted in lower capture rates at banding stations—suggesting that birds either hunker down to wait for conditions to improve, or leave the area. However, over longer periods of wildfire smoke, capture rates increased. The researchers suggested that birds respond to smoky conditions at first by reducing their activity, but as those conditions persist they may become more active to regain their body condition. The strength of these effects varied among species.
• Body Condition: By measuring individuals that had been captured at least twice in a season, the researchers could detect changes in body mass. Across 18 species, they found that body mass declined as the number of smoky days increased.
• Singing: A separate study in Singapore found that birds sang less during a period of widespread smoke in 2015.

Research Directions

As wildfires become more frequent and larger, continuing research into the effects of smoke will be important. Some promising areas for investigation include:

• using weather radar for remote sensing of migrating birds in the atmosphere.
• studying birds’ vocal behavior in areas before, during, and after fires or smoke events.
• using participatory science data such as eBird to discover patterns of change in birds’ distribution and abundance in response to fires and smoke.

Sources

Kittelberger, K. D., et al. (2022). Fall bird migration in western North America during a period of heightened wildfire activity. Avian Conservation and Ecology 17.

Lee, B. P. Y-H., et al. (2017). Smoke pollution disrupted biodiversity during the 2015 El Niño fires in Southeast Asia. Environmental Research Letters 12.

Nihei, A., et al. (2024). Wildfire smoke impacts the body condition and capture rates of birds in California. Ornithology 141.

Overton, C. T., et al. (2021). Megafires and thick smoke portend big problems for migratory birds. Ecology 103.

Sanderfoot, O. V., and B. Gardner. (2021). Wildfire smoke affects detection of birds in Washington State. Ornithological Applications 123.

Sanderfoot, O.V., and T. Holloway. (2017). Air pollution impacts on avian species via inhalation exposure and associated outcomes. Environmental Research Letters 12.

Sanderfoot, O. V., et al. (2021). A review of the effects of wildfire smoke on the health and behavior of wildlife. Environmental Research Letters.

Yang, D., et al. (2021). Unprecedented  migratory bird die-off: a citizen-based analysis on the spatiotemporal patterns of mass mortality events in the Western United States. GeoHealth 5.