The collision of migrating birds with human-built structures and windows is a world-wide problem that results in the mortality of millions of birds each year in North America alone. Birds killed or injured at such structures are due to two main factors. The first of these is the lighting of structures at night, which “traps” many species of nocturnal migrants. The second factor contributing to the hazard is the presence of windows, which birds in flight either cannot detect, or misinterpret. In combination, these two factors result in a high level of direct anthropogenic (human-caused) mortality. Bird mortality at human-built structures receives relatively little public attention, but structural hazards are actually responsible for more bird kills than higher profile catastrophes such as oil spills. The purpose of this report is to summarize what is currently known about migratory bird collisions, to investigate the seriousness of the threat, to present data on migratory bird mortality in central Toronto, and finally to make preliminary recommendations on how to help eliminate the problem.