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. And still the birds kept falling. “It was literally hailing birds,” Mesure says. “It was just a real sobering moment for us.”

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. The resulting brain damage is thought to kill about 60% of birds on impact, with many of the remainder left nursing chipped beaks or internal injuries that subsequently prove fatal. 

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. There are thought to be around 10 to 20 billion birds in the U.S., Loss says, so it’s not unreasonable to assume that up to 10% of the entire U.S. bird population dies, year-in, year-out, due to building collisions.

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. 

That kind of attrition can’t be sustained indefinitely, says Dan Klem, an ornithologist at Muhlenberg College who has spent the last four decades studying bird impacts. Population declines due to over-predation and other natural factors are self-correcting, Klem explains, since predators lose interest as numbers dwindle, and the fittest birds survive to rebuild the population. Windows, by contrast, are relentless in the toll they take, and kill both fit and unfit birds without distinction. “That in my opinion is what makes it so insidious and such a threat,” Klem says. “It’s so universal in its take.”

Reducing that take is easier said than done. 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. “That’s the holy grail of bird-friendly glass — a piece of glass that deters 100% of collisions but that looks just like normal glass to the human eye,” says Glenn Phillips, executive director of NYC Audubon. 

While that “holy grail” is still some way off, a growing toolkit is now available to designers and developers who want to create bird-safe buildings, says Christine Sheppard, head of the American Bird Conservancy’s building-impact program. Convincing people to actually make use of those tools remains a challenge, Sheppard says. Still, there are some positive signs: architects and developers appear enthusiastic about a new LEED credit being tested by the US Green Building Council, with 49 projects signing up for the credit in its first year. 

Some government bodies, too, are adopting bird-safe building regulations. Rep. Mike Quigley, a Democratic congressman representing northern Chicago, got the ball rolling during his time as a county commissioner, pushing through local bird-safety rules that have since been emulated in New York, Toronto and San Francisco. After heading to D.C., Rep. Quigley proposed a federal version of his bird-safe building ordinances, but received little support from perplexed fellow lawmakers. “I still get weird looks from people in Congress,” he says. 

Still, Rep. Quigley — who still finds himself checking the perimeters of large buildings for fallen birds — says he’s determined to keep working on the issue. For now, he’s quietly lobbying the General Services Administration to voluntarily adopt bird-safe standards for new public buildings. “We’re optimistic we can get something done,” he says.

Some activists aren’t willing to wait. In 2010, a coalition of environmental groups filed suit against the owners of Toronto’s Consilium Place, using FLAP’s bird-collection data to argue that the building breached Canadian environmental statutes. Though Consilium’s owners ultimately won, the lawsuit highlighted the risks being run by building operators who neglect bird-safety issues, says Brian Fowle, co-founder of architectural firm FXFOWLE. “That was a real eye-opener,” he adds. “We’re now actually at the point where you’re putting yourself at risk if you don’t deal with it.”

Consilium Place, meanwhile, is under new ownership, and has installed films printed with small white dots over its mirrored windows in a bid to ensure that birds don’t mistake glass for open sky. It’s still early days, says Mesure, but FLAP has already seen “a significant reduction in bird death” at the site. “My hat goes off to them — it’s a really big success story,” he says. 

Ben Whitford is the Ecologist’s US correspondent. He can be reached at mail@benwhitford.com.