The 2020 western U.S. fire season was among the most extreme on record. Over 100 fires were active in September, the majority occurring in California, Oregon, and Washington, where over 16,000 square kilometers burned. The 2020 fire season exemplified patterns of increased wildfire size, number, timing, return frequency, and extent, which are linked to climate-driven changes in precipitation and temperature affecting fire ignition and severity. Wildfires have increasingly coincided with the start of the fall bird migration and may present a growing risk to migratory birds. For example, the fall migration of the Tule White-fronted goose (Anser albifrons elgasi), a subspecies of Greater White-fronted goose (A. albifrons), occurred as smoke plumes from the wildfires reached the greatest extent.
The Tule goose has a limited breeding range near the Cook Inlet in Alaska and only a few thousand individuals exist. These low numbers have led to the designation of the Tule goose as a species of concern in California, where the wintering population resides within the Sacramento Valley. Beginning in the fall of 2018, biologists with the U.S. Geological Survey (USGS) Western Ecological Research Center worked with California and Oregon wildlife departments to radio-collar and track Tule geese from their principal stopover site at Summer Lake, Oregon. This region is used during both fall and spring migrations by virtually all Tule geese as they transit between Alaska and California.
In 2020, migrating geese encountered dense smoke extending into the Pacific Ocean and across migratory routes off the coast of Vancouver Island, British Columbia, Canada, and Washington. Comparison of GPS tracks from collared geese and the High-Resolution Rapid Refresh with Smoke (HRRR-Smoke) model allowed descriptions of individual response to dense wildfire smoke. Over the next several weeks, individuals encountering the smoke demonstrated several atypical migratory flight patterns, including backtracking and traveling around mountain ranges, extended at-sea stopovers off the Washington coast, approximately 4,000-meter (13,000-foot) flights over the smoke plumes, and loss of orientation toward traditional stopover areas (Summer Lake, Oregon). In total, these effects resulted in over 25% longer migration paths and a doubling of the migration duration between Alaska and Summer Lake. Researchers estimated these adaptations resulted in an energetic deficit sufficient to have caused increases in mortality or lowered reproductive outputs, which would require at least 4–6 days of elevated feeding activity to offset. Future monitoring of migratory bird populations using telemetry applications will continue to inform managers of the potential risk of wildfires to migrating bird populations.
Dense smoke (>161 micrograms/cubic meter) from wildfires in September 2020 covered an extent equivalent to 64% of California, Nevada, Oregon, and Washington combined. Migration paths of Tule geese (Anser albifrons elgasi) in 2020 (yellow in right panel) were more disorganized and resulted in longer migration times and distance flown relative to migration paths occurring in 2019 (blue in left panel) when dense smoke did not occur along migration routes. The associated manuscript is available here.
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