Continent-wide analysis of how urbanization affects bird-window collision mortality in North America

Abstract Characteristics of buildingsand land cover surrounding buildingsinfluence the number of bird-window collisions, yet little is known about whether bird-window collisionsare associated with urbanization at large spatial scales. We initiated a continent-wide study in North America to assess how bird-window collisionmortality is influenced by buildingcharacteristics, landscaping around buildings, and regional urbanization. In autumn 2014, researchers at 40 sites (N = 281 buildings) used standardized protocols to document collisionmortality of birds, evaluate buildingcharacteristics, and measure local land cover and regional urbanization. Overall, 324 bird carcasses were observed (range = 0–34 per site) representing 71 species. Consistent with previous studies, we found that buildingsize had a strong positive effect on bird-window collisionmortality, but the strength of the effect on mortality depended on regional urbanization. The positive relationship between collisionmortality and buildingsize was greatest at large buildingsin regions of low urbanization, locally extensive lawns, and low-density structures. Collisionmortality was consistently low for small buildings, regardless of large-scale urbanization. The mechanisms shaping broad-scale variation in collisionmortality during seasonal migration may be related to habitat selection at a hierarchy of scales and behavioral divergence between urban and rural bird populations. These results suggest that collisionprevention measures should be prioritized at large buildingsin regions of low urbanization throughout North America.