Unprecedented Migratory Bird Die-off: Citizen based Analysis of the Factors Influencing Mass Mortality Events in the Western United States

Extensive, severe wildfires and
wildfire-induced smoke occurred across the western and central United States
since August 2020. Wildfires resulting in the loss of habitats and emission of
particulate matter and volatile organic compounds pose serious threatens to
wildlife and human populations, especially for avian species, the respiratory
system of which are sensitive to air pollutions. At the same time, the extreme
weather (e.g., snowstorms) in late summer may also impact bird migration by
cutting off their food supply and promoting their migration before they were
physiologically ready. In this study, we investigated the environmental drivers
of massive bird die-offs by combining socioecological earth observations
datasets with citizen science observations. We employed the geographically
weighted regression models to quantitatively evaluate the effects of different
environmental and climatic drivers, including wildfire, air quality, extreme
weather, drought, and land cover types, on the spatial pattern of migratory
bird mortality across the western and central US during August-September 2020.
We found that these drivers affected the death of migratory birds in different
ways, among which air quality and distance to wildfire were two major drivers.
Additionally, there were more bird mortality events found in urban areas and
close to wildfire in early August. However, fewer bird deaths were detected
closer to wildfires in California in late August and September. Our findings
highlight the important impact of extreme weather and natural disasters on bird
biology, survival, and migration, which can provide significant insights into
bird biodiversity, conservation, and ecosystem sustainability.