After cats, what's the second biggest killer of birds? Windows. A new report finds that between 365 million and 988 million US birds, or as much as 10% of the country's bird population, die each year after flying into windows. And interestingly, skyscrapers account for less than 1% of those deaths, Science News reports. Buildings from four to 11 stories are biggest culprits, causing about 56% of the deaths, while one- to three-story buildings cause about 44% of the deaths.
Per building, however, skyscrapers are deadliest, with each one doing in an average 24 birds per year, compared to just a few birds per smaller building. But that's because there are just 21,000 skyscrapers in the country—compared to 138 million smaller buildings. Why are windows so dangerous to birds? One reason: Birds on long migration flights can be disoriented and confused by artificial lights at night. You can turn your lights off in an effort to help them out, or try bird-thwarting products like hawk stickers on your windows, Gawker reports. As for how the window deaths compare to deaths by cat, a study last year found that cats kill as many as 3.7 billion birds per year. (Read more birds stories.)