JACKSON HOLE, Wyo. — Research led by the University of Wyoming shows that extensive and severe wildfires, as well as wildfire-induced smoke, led to patterns of mass mortality events for various bird species in 12 Western states during the 2020 summer fire season. At the same time, snowstorms in late summer also may have impacted bird migration by cutting off the birds’ food supply and pushing their migration before the birds were physiologically ready to make the trip.
Di Yang, an assistant professor in the Wyoming Geographic Information Science Center, headed a research group that investigated the environmental drivers of massive bird die-offs by combining sociological Earth observation data sets with observations of citizen scientists.
“Migratory die-off events in the western U.S. are significantly related to smoke and toxic gases released from wildfires, combining with the heavy snowstorms in some areas by using a series of satellite images,” Yang says. “More importantly, citizens played an important role in observing this massive die-off event and provided invaluable data to iNaturalist, which is a citizen science platform.”
Yang is lead author of a paper, titled “Unprecedented Migratory Bird Die-Off: A Citizen-Based Analysis on the Spatiotemporal Patterns of Mass Mortality Events in the Western United States,” that was published in the April issue of GeoHealth. The open access journal publishes high-quality original research articles and commentaries across the intersections of the Earth and environmental and health sciences.
Other contributors to the paper were from Colorado State University, University of Georgia, Oregon State University and the University of Wisconsin-Madison.
The study investigated bird migration and survival from the perspective of global climate change, natural disasters and ecological disturbance. The study covered Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Texas, Utah, Washington and Wyoming. The American robin, barn swallows, flycatchers, mountain bluebirds and Wilson’s warblers were the bird species most frequently observed based on the death numbers reported, Yang says.
In Wyoming, during August and September, more birds were found in urban and forested areas compared with other types of lands. Cropland areas show a positive correlation with the number of bird mortality events in mid-September in eastern Wyoming. Translated, the more cropland cover there was in an area resulted in more dead birds found.
Overall, the study’s findings suggested that air quality and distance to wildfires were two major drivers that caused the severity of bird mortality rates. The closer distance to wildfires indicated a smaller number of bird deaths, except during mid-August to mid-September in California.
Regarding the distance to fires, birds have evolved to cope with fires and adjust migration pathways, Yang says. However, due to the lack of forest management practices, such as prescribed burning and removing some standing dead trees, the wildfires burned far hotter and were much larger, which made it difficult for the migratory birds to deal with.
“The toxic gases that were released from the smoke made an impact on the respiratory systems of migratory birds, and birds are very sensitive to the toxic gases during their exhausting long flights,” she explains.
During the August and September 2020 study period, numerous dead birds were found by citizen scientists and were reported on the citizen science platform.
The use of citizen scientists improved the accuracy of the study, Yang says, because their use significantly expanded the sample set. As a result, Yang and her research team were able to build a national-level model by adapting a quality-control framework to the citizen science data. For the identification of bird species in different regions of the West, volunteers have been proven to be as efficient as experts for this project, she says.
The study’s results also indicated that different land cover compositions affect bird mortality divergently over space and time, but with an increasing number of detections in urban areas.
The 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 stability. The findings also support calls for the efforts of the bird conservation program and the Migratory Bird Treaty Act to better take into consideration the interactions between environmental change and ecosystem sustainability.
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