Collisions with buildings cause up to 1 billion bird fatalities annually in the United States and Canada. However, efforts to reduce collisions would benefit from studies conducted at large spatial scales across multiple study sites with standardized methods and consideration of species‐ and life‐history‐related variation and correlates of collisions. We addressed these research needs through coordinated collection of data on bird collisions with buildings at sites in the United States (35), Canada (3), and Mexico (2). We collected all carcasses and identified species. After removing records for unidentified carcasses, species lacking distribution‐wide population estimates, and species with distributions overlapping fewer than 10 sites, we retained 269 carcasses of 64 species for analysis. We estimated collision vulnerability for 40 bird species with ≥2 fatalities based on their North American population abundance, distribution overlap in study sites, and sampling effort. Of 10 species we identified as most vulnerable to collisions, some have been identified previously (e.g., Black‐throated Blue Warbler [Setophaga caerulescens]), whereas others emerged for the first time (e.g., White‐breasted Nuthatch [Sitta carolinensis]), possibly because we used a more standardized sampling approach than past studies. Building size and glass area were positively associated with number of collisions for 5 of 8 species with enough observations to analyze independently. Vegetation around buildings influenced collisions for only 1 of those 8 species (Swainson's Thrush [Catharus ustulatus]). Life history predicted collisions; numbers of collisions were greatest for migratory, insectivorous, and woodland‐inhabiting species. Our results provide new insight into the species most vulnerable to building collisions, making them potentially in greatest need of conservation attention to reduce collisions and into species‐ and life‐history‐related variation and correlates of building collisions, information that can help refine collision management.
Cities can be regionalized in intra‐urban and peri‐urban areas. The space between urban areas and adjacent systems represents an ecological transition that often acts as a semi‐permeable biological filter. In this study, we assessed changes in avian community species richness, density, and composition at different peri‐urban ecotones (i.e., urban‐croplands, urban‐grasslands, urban‐shrublands) of northeastern Mexico City. Species richness was lower in the urban component of urban‐grassland and urban‐shrubland ecotones, while bird densities were higher in the urban components of the urban‐grassland and urban‐shrubland peri‐urban ecotones, mainly due to the high number of urban exploiter species. However, the urban‐cropland peri‐urban ecotone exhibited a different pattern, with similar low bird species richness and density values between both components (urban and non‐urban). A species composition analysis revealed that urban bird communities were not influenced by adjacent non‐urban habitats, since the urban components of peri‐urban ecotones were more similar among them than in relation to the rest of non‐urban components. In summary, results of this study show that urbanization can represent an important biological filter for birds, often reducing species richness and homogenizing avian communities at local scales. As the environmental variables determining ecological processes related to the semi‐permeable filter effect that urban areas pose to biodiversity might depend on urban habitats, regions, and spatial scales, further studies are needed to fully understand this phenomenon.
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