Modeling Bird-Window Collisions in Core Urban Environments

Abstract

Birds contribute to ecosystem function and deliver ecosystem services to human societies. However, birds are threatened by multiple anthropogenic stressors. Although window strikes are only one among many threats, they have received attention, a prominent example being public concern that the U.S. Bank Stadium’s massive glass gates could result in bird deaths. We can mitigate bird–building collision mortality with bird-safe glass. However, targeted intervention requires models that predict where losses are greatest. With this objective, I assessed spatial drivers of collisions using data provided by research partner Audubon Minnesota. These data, collected by volunteer citizen scientists and skillfully managed by staff, recorded bird collisions in the Twin Cities during migration seasons (2007–2016). I assessed the influence of vegetation on collisions while also exploring how spatial scale affected that relationship. In addition, I compared collisions at skyways versus buildings. To complement this spatial study, I conducted a distinct investigation in the same location during the breeding season (2016). I measured local bird abundance using point counts, and concurrently, surveyed the area for collisions. Of 14 total species, only 3 were counted both alive and in collisions. I used generalized linear mixed models to determine that after abundance is accounted for, species designations did not explain collision counts. However, a trait that may influence collision susceptibility is body mass, suggesting that small birds are more likely to collide than large birds. Lastly, I estimated that 6% of local birds succumb to collisions. Although cities contain hazards for birds and other wildlife, they also contain observers who can help shed light on how ecological processes are affected by urbanization. This is especially relevant in our increasingly urbanized world where conservationists engage city dwellers to protect and appreciate biodiversity.