A First Estimate for Canada of the Number of Birds Killed by Colliding with Building Windows

Mortality from birds colliding with windows in buildings may be ecologically significant. Although data are sparse, we estimated the number of birds killed by this means in Canada. We made distinct models for three classes of buildings: houses, low-rise commercial and institutional buildings, and tall buildings. Estimates were developed using Monte Carlo-based simulations incorporating uncertainties and based on distributions that best fit available data or conceptual models. We estimate that about 25 million (range 16 - 42 M) birds are killed by colliding with windows in Canada annually. The assumptions used in our analyses are identified in detail so that subsequent efforts can address the uncertainties. Houses likely cause 90% of building-related mortalities, low-rise buildings slightly less than 10%, and tall buildings approximately 1%. The disproportionate contribution of mortality caused by houses is a function of their relative number compared to the two other classes of buildings. Our review found that warblers and sparrows were the most commonly killed birds at low-rise and tall buildings, and insufficient information exists on species deaths at houses to determine proportions. Targeted mitigation for certain tall buildings and a segment of the low-rise building types could significantly reduce the total mortality for both these building types. Mitigation strategies are now widely available, including architectural guidance produced by numerous cities in North America as well as specific products suitable for home use to reduce the number of birds colliding with windows.