What causes bird-building collision risk? Seasonal dynamics and weather drivers

Authors: Kara M. Scott1 | Attilla Danko2 | Paloma Plant3 | Roslyn Dakin1

1Department of Biology, Carleton
University, 1125 Colonel By Drive,
Ottawa, Ontario K1S 5B6, Canada
2cleardarksky.com, Ottawa, Ontario,
3Fatal Light Awareness Program Canada,
PO Box 430, Toronto, Ontario M5C 2J5,

Year: 2023

Publication: Ecology and Evolution

Publication Link: https://doi.org/10.1002/ece3.9974

Keywords: aeroconservation, birds, building collisions, conservation, migration, mortality, weather

Abstract: Bird-building
collisions are a major source of wild bird mortality, with hundreds of
millions of fatalities each year in the United States and Canada alone. Here, we use
two decades of daily citizen science monitoring to characterize day-to-
variation in
building collisions and determine the factors that predict the highest risk times in two
North American cities. We use these analyses to evaluate three potential causes of
increased collision risk: heightened migration traffic during benign weather, increased
navigational and flight errors during inclement weather, and increased errors in response
to highly directional sunlight that enhances reflected images. The seasonal
phenology of collisions was consistent across sites and years, with daily collision rates
approximately twofold higher in autumn as compared to spring. During both migration
seasons, collision risk was best predicted by the weather conditions at dawn. In
spring, peak collision risk occurs on days with warm temperatures, south winds, and
a lack of precipitation at dawn. In autumn, peak collision occurs on days with cool
temperatures, north winds, high atmospheric pressure, a lack of precipitation, and
clear conditions with high visibility. Based on these results, we hypothesize that collisions
are influenced by two main weather-driven mechanisms. First, benign weather
at dawn and winds that are favorable for migration cause an increase in migration
traffic in both spring and autumn, creating greater opportunity for collisions to occur.
Second, for autumnal migrants, cold clear conditions may cause an additional increase
in collision risk. We propose that these conditions may be particularly hazardous in
autumn because of the high abundance of naïve and diurnal migrants at that time of
year. Our analysis also establishes that a relatively small proportion of days (15%) are
responsible for 50% of the total collision mortality within a season, highlighting the
importance of targeting mitigation strategies to the most hazardous times.

Leave a Reply

Your email address will not be published. Required fields are marked *