Hundreds of millions of birds are killed in collisions with windows each year in the U.S. alone, and although high-rise buildings tend to be the biggest individual culprits, the vast number of suburban homes across the continent means that even a few deaths per house add up fast. A new study in The Condor: Ornithological Applications examines the factors that affect window collision rates at homes and shows that yards that are more attractive to birds are also the sites of more collisions.Working with Alberta homeowners who collectively contributed more than 34,000 days' worth of collision data, Justine Kummer of the University of Alberta and her colleagues found that the presence of a bird feeder, whether a house was in an urban or rural area, and the height of the vegetation in the yard were the most important predictors of collisions. Of Alberta's 421 bird species, 53 were represented in the data, mostly common urban species.