According the a study of bird feeding in the United States and Canada called ProjectFeederWatch, window strikes are responsible for more deaths at feeders than cats, hawks or any other factor.
This conclusion is based more than 2,000 deaths reported during the study. According to the analysis of these data, nearly half of all deaths are caused by birds striking windows. If these data are correct, the study leaders estimate that one in ten birds might be killed by flying into buildings annually.
While this is indeed a cause of concern to those of us that feed birds in our backyards, these deaths might represent only two or less percent of North America’s fall bird population.
This conclusion is based on volumes of data collected by literally thousands of citizen scientists that submitted detailed logs a wide range of subjects relating to their bird feeding programs.
This monumental study was sponsored by the Cornell Laboratory of Ornithology, Bird Studies Canada, National Audubon Society, and the Canadian Nature Federation.