Early Evidence of How Wildfire Smoke Alters Bird Migration

This story originally appeared on High Country News and is part of the Climate Desk collaboration.

Four radio-collared Tule geese left their summer breeding grounds near Alaska’s Cook Inlet in the fall of 2020 to head south for the winter. The migration typically takes about four days: The birds fly over the Gulf of Alaska, stay about 100 miles offshore from Canada, and skirt Vancouver Island. They stop briefly to float and rest on the Pacific Ocean a handful of times and then gather en masse at Summer Lake in central Oregon before making the final push to California’s Sacramento Valley. Last summer, however, the migrating birds encountered dense wildfire smoke off the coast of British Columbia and over Washington—and that’s when their behavior got weird. 

One bird backtracked north almost 80 miles. Two spent nearly four days floating on the ocean before trying to head inland again; they ended up flying directly at the Beachie Creek Fire in Oregon and then climbing almost four times higher than usual to get over the huge plume of smoke. A fourth bird got turned around and headed much farther east than normal, all the way to Idaho. Tule geese typically prefer to overnight at wetlands, but these four stopped in bizarre locations instead, even landing once on the side of Mount Hood.

According to a study released by the U.S. Geological Survey (USGS) in early October, the birds’ 2020 migration took twice as long as the 2019 migration—nine days versus four—and they flew an additional 470 miles, all to avoid wildfire smoke. The paper states that “megafires and thick smoke portend big problems for migratory birds” as wildfires increasingly coincide with the beginning of fall migration. There were 68 active fires in California, Oregon, and Washington when the geese passed through. Lengthier migrations require more energy and take more time to recover from. That could make it harder for the birds to reproduce, and even put them at risk of dying.

Cory Overton, a wildlife biologist at the USGS Western Ecological Research Center and the paper’s lead author, was watching the birds’ disjointed flights in real time, via GPS tracking. “I was glued to my computer for days, trying to figure out what these birds were doing because it was so clearly, obviously, not normal,” Overton said. All four birds did, however, eventually make it to their preferred stopover in Oregon. 

Overton and his colleagues believe this marks the first time scientists were able to definitively document how wildfire smoke alters bird migration. The birds began to change their behavior when encountering fine particulate matter of 161 micrograms per cubic meter, which is just over the Environmental Protection Agency’s threshold for “very unhealthy” air for humans. Migrating birds across several Western states were found dead and dying the same summer and early fall, and other research found a correlation between the deaths and toxic air. 

Tule geese, a subspecies of the greater white-fronted goose, are a “species of special concern” in California due to their low population numbers; there are fewer than 10,000 of them. They’re especially vulnerable to flight obstacles because they follow the same route and stop at the same spots yearly. Overton and his colleagues were also tracking 12 additional waterfowl species, all of which migrate later in the fall than Tule geese. Smoke was almost gone from the Pacific Northwest by the time the others journeyed through the region. But as fire seasons in the West lengthen, scientists are concerned that smoke may hinder more migrations along the Pacific Flyway. Many shorebirds and songbirds are unable to store the extra energy needed to reroute around fires.