Early Evidence of How Wildfire Smoke Alters Bird Migration

This story was originally published on High Country News. It is part of the Climate Desk collaboration.
Four radio-collared Tule geese, four radio-collared, left their summer breeding grounds at Alaska's Cook Inlet in fall 2020 to head south for winter. The migration takes approximately four days. The birds fly over the Gulf of Alaska, then stay 100 miles offshore of Canada and skirt Vancouver Island. The birds stop briefly to rest and float on the Pacific Ocean for a few times before gathering at Summer Lake in central Oregon to make the final push towards California's Sacramento Valley. However, last summer the migrating birds came across dense wildfire smoke from British Columbia and Washington, which caused their behavior to change.

One bird flew backwards almost 80 miles. Two birds spent almost four days floating on ocean waves before trying to return to land. They ended up landing directly at the Beachie Creek Fire, Oregon, and then climbing nearly four times as high as usual to clear the massive plume of smoke. The fourth bird turned around and flew east, much further than usual, all the way to Idaho. Although tule geese prefer to stay overnight in wetlands, these four birds stopped at bizarre places instead. One of them even landed on Mount Hood.

A study by the U.S. Geological Survey was released in October. It revealed that the 2020 migration took twice the time as the 2019. The birds flew an additional 470 mile to avoid wildfire smoke. According to the paper, "megafires" and thick smoke are a problem for migratory birds as wildfires often coincide with fall migration. The geese flew through 68 active wildfires in Washington, Oregon, California when they passed. Longer migrations take more energy and require longer recovery times. This could make it more difficult for birds to reproduce and increase their risk of death.

Cory Overton is a USGS Western Ecological Research Center wildlife biologist and lead author of the paper. He was monitoring the birds' disjointed flight movements via GPS tracking. Overton stated, "I was glued my computer for days trying to figure out why these birds were doing it because it was so clearly not normal." However, all four birds made it to Oregon, where they were most comfortable.

Overton and his collaborators believe that this is the first time scientists have been able to document the effects of wildfire smoke on bird migration. Fine particulate matter (160 micrograms per cubic meter) was the threshold that Environmental Protection Agency considers "very unhealthy" for humans. This is what caused birds to alter their behavior. Many migrants died in the same season as their Western counterparts. Other research also found a link between toxic air and the deaths.

California's "Species of Special Concern" is Tule Geese. They are a subspecies the greater white-fronted goose. There are less than 10,000 of them. Because they travel the same route each year, and stop at the same places every year, they are particularly vulnerable to flight hazards. Overton and his associates were also monitoring 12 other waterfowl species. All migrate later than Tule geese in the fall. The smoke was almost gone in the Pacific Northwest when the other birds passed through it. Scientists are worried that more people may be unable to migrate along the Pacific Flyway due to the longer fire seasons in West. Many songbirds and shorebirds cannot store the extra energy required to reroute around fires.