Many happy hours can be spent gazing at the birds we've attracted to our yards with feeders and native plantings. But the same windows that allow us to view outside can be dangerous for birds. Window strikes are considered one of the most significant causes of bird mortality, with as many as 900+ million birds killed per year in the United States alone.
A 2020 review of research on bird-window collisions found that some species collided more than others (these "super colliders" include the White-throated Sparrow, above) due to their behavior and migratory status. Building glass is particularly dangerous when panes are large and they reflect surrounding vegetation, or when the windows are in close proximity to green areas such as urban parks or bird feeding stations. The authors also noted that most studies were conducted in North America, highlighting the need for additional research elsewhere.
Reducing or disrupting window reflections can help birds. The American Bird Conservancy offers guidance on ways you can prevent bird collisions and they maintain a database of effective products. For example, you might consider leaving window screens in place over the winter, keeping window blinds partially open, making a zen curtain, or applying decals to the outside of your windows.