Wildfire Smoke Disrupts Bird Migration in the West
by Paul Laustsen and Allie Weill, U.S. Geological Survey
October 13, 2021
SACRAMENTO, Calif. – Early fall wildfires in the western states and the smoke they generate pose a risk to birds migrating in the Pacific Flyway, according to a new study by the U.S. Geological Survey. GPS data from the 2020 wildfire season indicate that at least some migratory birds may take longer and use more energy to avoid wildfire smoke.
Wildfires have increasingly coincided with the beginning of fall migration for many bird species. This greater frequency of fall wildfires is thought to be primarily the result of frequent drought conditions and climate change, and the impacts of these fires on migrating birds are not yet well documented. Since 2018, researchers from the USGS Western Ecological Research Center have marked tule geese (a subspecies of the greater white-fronted goose that breed in Alaska and northern Canada and winter in Washington, Oregon and California as well as Texas, Mexico and Central America) with GPS-tracking devices. This is part of a larger program to study the movements and behavior of migratory waterfowl in the Pacific Flyway in real-time.
In September 2020, four GPS-marked tule geese encountered dense wildfire smoke while flying through the Pacific Northwest in the first part of their migration. By matching up the GPS tracks with a three-dimensional model of the smoke during the time of the migration and comparing them with migration tracks from 2019 (a year without heavy smoke), researchers were able to assess how the wildfire smoke disrupted the geese’s flight paths.
“Everything coincided such that we could watch this unfold in almost real time,” said Cory Overton, a USGS wildlife biologist and lead author on the study. “It’s virtually impossible to see this type of event without preparedness and good fortune – you can’t design a study to look at an unprecedented fire season. And then to have all four individuals survive long enough to get the data to us? It’s pretty incredible.”
The geese responded to dense smoke by pausing their migrations, altering the direction or altitude of flight, or both. Some geese stopped their flight for two to three days until the smoke cleared. Geese that flew through smoke or directly over fires had disorganized flight paths, sharp increases in altitude to fly over the smoke plume, and stopovers in non-traditional habitats far from traditional migratory pathways. All of the marked geese eventually arrived at their destination of Summer Lake, Oregon, but the average migration in 2020 took twice as long as in 2019 (nine versus four days) and covered an additional 470 miles (757 km).
These longer and farther flights resulted in much higher energy expenditure than a typical migration. The study estimates that the geese would need several extra days to recover from the resulting caloric deficits. These energy deficits could lead to increased mortality or lower reproductive rates, suggesting that smoke disruptions could ultimately put vulnerable migratory bird populations at greater risk.
Read the Ecology paper: https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.3552