Birds & Buildings: Bird-Window Collisions in the Urban Landscape

Abstract

Bird collisions with buildings are the second largest anthropogenic source of direct mortality for birds (365-988 million birds killed annually in the United States). To investigate the factors that affect bird-building collisions from both the building and the avian perspective, I make use of the high quality avian collision data collected by a citizen science effort to monitor and rescue birds that collide with buildings: Minnesota Project BirdSafe. Through the program, citizen scientists walked routes in Saint Paul and Minneapolis that include buildings almost daily spring and fall migration for 10 years. I used the data collected by these citizen science volunteers to assess building and landscape factors contributing to bird-building collisions and to identify patterns in bird-building collisions based on taxonomy and behavior of birds. Findings from building and landscape analysis highlight importance of differences in building collision dynamics between spring and fall migration, the increased risk of collisions for buildings that are close to migratory stopover habitat, and using edge:area ratio of buildings rather than percent glass as a predictor of bird-building collisions. Findings from analyses of avian risk for collisions indicate that birds that predominately migrate during the day have a decreased risk of building collisions despite peak collision numbers occurring during early morning. Additionally, for many species, local abundance is the predominant determining factor for collision risk. However, for ~20% of species studied, the family, genus, and/or species of a bird may increase or decrease collision risk beyond what would be expected from abundance alone. Lastly, comparative analysis of multiple sources of avian abundance data (local point count, local banding data, eBird data, and Breeding Bird Survey data) reveal generally comparable results when used for analysis of bird-building collision risk; thus while current understanding of species collision risk is spatially restricted, but pre-existing citizen science data could allow for analyses in any location with bird-building collision data; improving our understanding of which birds are most in need of protection from bird-building collisions.