Photo: NYC wildfire smoke, Metropolitan Transportation Authority, CC BY 2.0, via Wikimedia Commons
Deidra Bryant
NYC wildfire smoke, Deidra Bryant
I remember how orange the skies were at my parents’ home in New York, as well as the numerous environmental health and air quality advisories issued in the Washington, DC area due to the intense Canadian wildfires in spring and summer 2023. Did you know that about 60% of wildfire smoke in the Northeast in recent years came from fires outside the United States (Burke, et al., 2021)? We humans can find some refuge from the toxic particles by entering an office building, or staying at home, but what do birds do? Do they fly away? Do they stay? How does the smoke damage their bodies and how does this affect their ability to survive in the seasons afterward? These questions need answers: they are concerns raised for many years but not studied nearly enough.
Of course, wildfires aren’t inherently bad. In fact, wildfire has been part of the ecology of forests for millions of years. Certain trees and their pods, like the lodgepole pine (Pinus contorta) or the jack pine (Pinus banksiana) in the north and northwest, need fire to “unlock” their seeds. The longleaf pine (Pinus palustris) in the southeast also requires wildfire for forest regeneration, because fire clears out the undergrowth that can block seeds from getting to the soil. Fires also make more habitat for early successional species and for specialist species such as the Black-backed Woodpecker (Picoides arcticus) and the Red-cockaded Woodpecker (Dryobates borealis). But recently wildfires are occurring earlier in the year, covering a larger area, becoming more intense, and occurring more frequently. The increase in lethality of these wildfires is due to climate change, making habitats unsuitable for species dependent on mature forests, causing damage to bird nests and their eggs, and creating risks from noxious gas inhalation.
In the past, coal miners would bring canaries, a sentinel species, down with them in cages to the mines to act as living alarms to signal danger from harmful gas exposure. Because canaries were more sensitive to the dangerous gasses found in the mine shafts and were quicker to succumb to the effects of exposure than humans, a display of erratic activity from the birds gave miners a chance to escape or put on protective gear. Although evidence existed for canaries responding to hazardous gasses for centuries, very little research has been done on how smoke affects wild birds.
A recent study performed in California’s Bay Area, published this year, found consistent evidence that acute and chronic exposure to smoke can affect avian body mass in passerines. Results suggested that the tiny bodies of songbirds may expend more energy in order to mitigate the sublethal health effects associated with prolonged or frequent smoke exposure, causing weight loss (Nihei, et al., 2024). A decrease in the body mass of a songbird is a very significant concern considering their ability to migrate successfully depends on whether they are able to consume enough calories to make the long trip. Additionally, if songbirds become ill or stressed due to the presence of smoke, they may reduce their movements altogether. This inactivity is NOT good if migration, or simply relocating locally, is necessary to reach a habitat rich in food as well as a habitat that provides a suitable climate for regulating body temperature. Results also suggested that once air quality improves, affected birds may become active again in order to make up for lost time foraging.
One must also keep in mind that although wildfires may affect a variety of birds in an area, the physiology and necessary habitat of each bird species varies, too, and their response to smoke inhalation is likely species-specific. For instance, avian responses to smoke may depend on their ability and willingness to seek new shelter. Birds with larger home ranges or less site fidelity may be more inclined to leave an area affected by smoke compared to birds that are restricted to smaller home ranges or highly specific locations (Sanderfoot and Gardner, 2021). This is a concern for shorebirds and even certain owls in northern Virginia, such as Barred Owls, that have high site fidelity. Another concern is the release of corticosterone (a primary stress hormone) as a metric for determining bird behavior when exposed to smoke. Species that release a little of the hormone might have a more active behavioral response to the stressor, whereas a bird that produces a lot of the hormone might have a more passive response to the wildfire and smoke stressors (Cockren, 2013).
Large-scale wildfire smoke events are happening more frequently and across increasingly broad areas of the world (Jolly, et al., 2015), posing increased risks to birds as an environmental stressor. However, birds (like people) can have different responses to both acute and chronic smoke exposure. This complexity of avian responses to smoke requires researchers to develop meaningful exposure metrics for wildlife studies. It is crucial to understand how the duration, extent and intensity of smoke exposure affects the health and behavior of wild birds. Northern Virginia, or the Washington, DC area for that matter, has not experienced wildfires like Hawaii, California, or Oregon, because Virginia has an Eastern deciduous forest biome with a humid subtropical climate that is more prone to flooding than forest fires. However, the smoke blowing down from places that DO have frequent fires (such as the boreal forests of Canada) are a recurring issue. Taking advantage of this phenomena by performing more experiments not only on the west coast, but also in the New England/mid-Atlantic area of the U.S. will greatly help in understanding how highly stressful wildfires, caused by climate change, affect migratory and resident birds alike.