Window collisions by migratory bird species: urban geographical patterns and habitat associations

Bird collisions with buildings are an increasing concern and yet understanding the factors contributing to collisions at the species level remains largely unknown. This gap in our knowledge of species-specific strike patterns hinders the development of accurate estimates for the impact of death-by-collision on bird populations and impedes on our ability to minimize its effects. Our study offers the first examination of the impact of environmental variables on bird-window collisions at the species level. The Fatal Light Awareness Program Canada collected bird-window collision data in three distinct regions of Toronto, Canada during the migratory season of the years 2009 and 2010. Our results indicated that building percent window cover, exposed habitat cover, and cover of built structures significantly affect bird-window collisions. Multivariate analyses showed that the bird species that collided with buildings surrounded by a high level of urban greenery are species that typically occur in forested habitats and are foliage gleaners. In contrast, species that collided with buildings surrounded by a higher level of urbanization are species that typically occur in open woodland and are ground foragers. These results suggest that the composition of bird species colliding with buildings across various regions of the Greater Toronto Area is influenced by the local bird species community composition, by the configuration of the surrounding landscape, and by the levels of greenery around the buildings.