Article: Predicting Bird-Window Collisions with Weather Radar by Elmore and colleagues (2021)
Background: Every year, nearly 1.5 billion birds die as a result of colliding with man-made structures in the United States (Loss et al., 2015). Several factors play a role in predicting when these collisions occur: migratory patterns, flight speed, flight altitude, and time of day. Most collisions occur at night as artificial light disorientates birds and disallows them from identifying clear, safe flight paths. Losing such a large number of birds has seed dispersal, pollination, and pest control consequences, so it is important to develop strategies for monitoring bird flight and predicting bird collisions. Effective techniques will allow us to mitigate bird collisions, thus resulting in a potentially large decrease in bird fatalities annually.
Methods: Elmore and colleagues conducted morning surveys (7:00-9:00 am) at 17 buildings In Stillwater, Oklahoma during the fall and spring migrations to observe bird fatalities. The number of fatalities were compared to night migratory pattern information (e.g., migration traffic, speed, altitude) derived from the NEXRAD network (radar surveillance; scans the airspace every 5-10 min).
Findings: The researchers conducted 3857 collision surveys and documented 304 bird fatalities. Of these birds, 227 were considered migratory birds (e.g., Warblers, Thrushes, Hummingbirds, and Sparrows), so they were used for further analyses. Migration traffic rate (i.e., number of birds crossing a line perpendicular to the migration direction) was found to be the only factor associated with bird fatalities; an increase in migration traffic rate resulted in an increase in bird fatality.
Conclusions: Although the sample size was small (i.e., number of fatalities and number of surveys), Elmore and colleagues found an important association between a radar-derived migratory factor and bird fatality. Because Stillwater, OK is a small city, the characteristics of larger cities (e.g., larger buildings, more light pollution, etc.) would likely lead to an enhanced effect on bird fatality. Since migration traffic rate and increasing artificial light at night are associated with bird fatality, decreasing artificial light during nights with high predicted migration traffic rates could prevent a large number of bird deaths. Further, incorporating radar and weather surveillance would allow for even better predictions of bird movements, since weather is known to impact bird migratory patterns, flight altitude, and flight speed. Implementing this technology in large and small cities and advocating for policies aimed at reducing light pollution can help protect bird biodiversity.
Figure: Radar map of Stillwater, OK and surrounding area. The three black dots represent the NEXRAD radar sites. The values (dBZ) are relative to the size of the object that can be detected.
Reference:
Elmore, Jared A., et al. "Predicting bird‐window collisions with weather radar." Journal of Applied Ecology.
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