Year-round monitoring at a Pacific coastal campus reveals similar winter and spring collision mortality and high vulnerability of the Varied Thrush. Issue 3 (23rd June 2021)

• Record Type: Journal Article
• Authors: De Groot, Krista L; Porter, Alison N; Norris, Andrea R; Huang, Andrew C; Joy, Ruth
• Is Part Of: Ornithological applications. Volume 123:Issue 3(2021)
• Publication Date: 2021-06-23
• Subjects: anthropogenic threats -- bird conservation -- bird mortality -- bird–window collisions -- building collisions -- collision monitoring -- urban ecology -- urban threats vulnerability; menaces anthropiques -- conservation des oiseaux -- mortalité aviaire -- collisions d'oiseaux aux fenêtres -- collisions contre les édifices -- suivi des collisions -- écologie urbaine -- vulnérabilité aux menaces urbaines; Birds -- Periodicals; Birds -- California -- Periodicals; Ornithology -- Periodicals; 598
• DOI: 10.1093/ornithapp/duab027
• Languages: English
• ISSNs: 2732-4621

Abstract

Abstract: Bird–window collisions are a leading cause of direct anthropogenic avian mortality, yet our state of knowledge regarding this threat relies heavily on eastern North American studies. Seasonal patterns of collision mortality may differ along the Pacific coast, and western North American species remain understudied. We therefore surveyed a stratified random sample of 8 buildings for collisions at the University of British Columbia, Vancouver, Canada over 45-day periods during 2 winters, 1 spring, 1 summer, and 1 fall season between January 22, 2015 and March 15, 2017. After accounting for the rate of scavenging and efficiency of observers in finding carcasses, we estimated that 360 collision fatalities (95% CI: 281–486) occurred over 225 days of collision monitoring. Collision mortality was highest in fall, but in contrast to most published research, collision mortality was intermediate in both winter and spring and was lowest in summer. In winter 2017, we performed point-count surveys to assess whether individual species are disproportionately vulnerable to collisions when accounting for population size and found that the Varied Thrush ( Ixoreus naevius ) was 76.9 times more likely to collide with buildings, relative to average species vulnerability in winter. To our knowledge, this is the first study to report the Varied Thrush as a species that is disproportionately vulnerable to collisions. Further studies are needed to assess the vulnerability of Western North American species and subspecies, and to determine whether similar patterns of seasonal collision mortality are found elsewhere. Lay Summary: Between ~381 million and ~1.3 billion birds are killed each year by colliding with glass in the United States and Canada alone, but we know little about how collisions affect western North American birds throughout the year. We monitored 8 buildings for collisions at the University of British Columbia in Vancouver, British Columbia and estimated that between 281 and 486 birds were killed by collisions at our study buildings over five 45-day monitoring periods across all seasons between January 22, 2015 and March 15, 2017. Collisions with glass were most prevalent during the fall migratory season but collision mortality was also prevalent in winter and during spring migration. We calculated species vulnerability to collisions in winter 2017 and found that the Varied Thrush was most vulnerable to collisions; colliding 76.9 times more frequently than expected at our study site. Graphical Abstract: