Almost 1,000 Birds Died in One Night From Striking a Chicago Building

But the city isn’t alone: Across the United States, between 365 million to about 1 billion birds die each year from colliding with glass in skyscrapers and low-rise buildings. Window strikes are the second-leading cause of bird deaths, behind cats. (Other human-caused threats, such as habitat loss, almost certainly kill more birds, but those are much harder to measure.)