Bird Strike: deaths caused by collisions with buildings severely dent populations

On a brisk May morning in 2001, countless dying birds fell like rain from the grey Toronto sky. In the east of the city, outside a hulking 18-storey office complex called Consilium Place, workers on cigarette breaks watched in horror as tiny feathered bodies thudded onto the pavement, fell into their laps, and crashed onto the picnic tables where they had laid out their coffee and morning snacks.

While the office workers sought shelter, a bird enthusiast named Michael Mesure called for backup. As founder of the Fatal Light Awareness Program, or FLAP, Mesure runs a team of volunteers who patrol Toronto in search of birds that have stunned themselves — or worse — by flying into one of the city’s many mirrored-glass skyscrapers. Some mornings Mesure’s team doesn’t find many birds: perhaps just one, or two, or twenty. 

In the space of six hours on that May morning, though, Mesure and a dozen or so volunteers found at least 500 birds. Ruby-throated hummingbirds, dark-eyed juncos, white-throated sparrows and Nashville warblers were carefully collected: the tiny corpses stored in plastic bags, the injured survivors placed gently in paper sacks for treatment and subsequent release

On a smaller scale, experts say, such scenes are repeated daily across North America as birds, unable to distinguish between blue sky and what Vladimir Nabokov poetically called “the false azure in the windowpane”, careen into windows at speeds of up to 30 miles per hour.

In all, it’s estimated that the Toronto skyline accounts for about 1 million bird deaths a year — and even that is just a drop in the bucket. It’s hard to put a precise number on collision-related mortalities, but researcher Scott Loss of the Smithsonian Institute is preparing to publish new research that, based on a sophisticated analysis of 23 previous studies, estimates that between 400 million and 1 billion birds die from window impacts each year in the U.S. alone.

That eye-popping number suggests that window impacts are putting a serious dent in the North American bird population. 

Troublingly, too, there’s evidence that North America’s most vulnerable species are disproportionately affected. According to Loss’s data, at-risk species including hummingbirds, woodpeckers and various warblers are between 12 and 35 times more likely than the average bird to collide with buildings, perhaps because their migratory routes take them through skyscraper-filled cities such as Toronto, New York and Chicago. 

After a series of false starts, much of the research in the field now focuses on developing unobtrusively patterned glasses or films that birds interpret as solid obstacles. Perhaps the most promising technology under development is a kind of glass that alternately reflects or absorbs ultraviolet light, creating patterns that are visible to birds but not to humans. 

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