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On a chilly day in Toronto, Michael Mesure, executive director of a local bird conservation group, leads me up several flights of stairs in City Hall. We walk down a hallway and there stands a large, white chest—a freezer—with a lid straining to close against its contents. Mesure removes a heavy Rubbermaid bin to reveal dozens of migratory birds of every size and plumage—hermit thrushes, common yellowthroats, white-crowned sparrows. Some look mummified in Saran wrap; others are frozen in plastic bags. There’s at least a hundred inside. “This is barely a sample of the birds we’ve picked up,” says Mesure.

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Mesure is the founder of Fatal Light Awareness Program (FLAP) Canada, one of several nonprofit groups drawing attention to the fatal problem that bright city buildings present to birds. He and FLAP volunteers rescue injured birds and collect the dead each spring and fall, when the birds take wing along the four major “flyways” across North America to breed or feed. A single species might pass through both New York City and Miami on its journey. Though migration has always carried risks, the journey has become increasingly perilous for those that pass through the continent’s rising city skylines. Mesure says a single office complex in Toronto killed 500 birds in six hours. “You’d be picking up one bird, and one or two would fall on your back as you’re picking it up,” he says. “It was insane.”

Mesure isn’t sure exactly how many die each year—the data are difficult to collect, and historical estimates are rough. But recent studies put the number of birds killed by collisions with buildings, in North America alone, at 300 million to 1 billion. Ironically the reason for the death toll has to do with birds’ finely tuned navigational sense.

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Like many migratory animals, birds have an inborn sense for navigation. Long-distance migrants, explains Bridget Stutchbury, a conservation ecologist studying songbird migration, use the position of the sun and stars—celestial navigation—to get their bearing. But in a situation where that’s not possible, like travelling on a cloudy night, they can fall back on an in-built compass. How this mechanism works remains unclear; some researchers think that minute amounts of magnetite or iron in a bird’s head allow them to sense the earth’s magnetic field. One study, published in 2011 in arXiv, even suggests quantum entanglement could somehow be involved. Birds also seem to learn from certain experiences. Ones that have made a migratory journey before appear to move faster and more efficiently from place to place, and they recognize visual landmarks.

But what the birds don’t seem to learn is that major cities—during day or night—can be serious migratory hazards. On foggy nights, migrant birds confuse building lights with stars, drawn toward the inverted sky of the city, and during the migration season in New York, thousands of birds are swept into the spotlights of the Twin Towers memorial, aimlessly circling the bright shafts; if necessary, the lights are turned off for a few minutes, allowing the spell to break and the birds to move on. Many cities try to turn off the lights on major buildings during migration periods, but billions of birds still end up in scanty patches of habitat in suburbs and downtown areas.

During the day they can’t tell the difference between a pane of glass and what it’s reflecting. The patches of greenery in office lobbies, along with the sky and images of trees and parks reflected off commercial buildings, also look inviting; birds, foraging desperately to refill their energy reserves, will fly straight into the windows, dying on impact or falling concussed to the ground. Hundreds of millions of them end this way, but many more may perish as easy prey for domestic and feral cats if they survive the fall. Mesure says studies that rely on pet-owner surveys don’t determine whether domestic cats are actually killing the birds or just finding their remains, as owners only know how many carcasses end up on their doorstep.

It’s a huge problem—but there’s a relatively simple solution. If you look closely at large, ground level panes of glass in malls, there’s usually a logo or a band of color at eye level to prevent you from crashing into them. Now, scientists and engineers are applying the same principle to stop window collisions. Mesure has a variety of patterns in his office as examples—dots, stripes, thick bands—that promise to end birds’ perceptual confusion. Denser patterns work best, Mesure explains, because they are the most visible, but many buildings are reluctant to install obtrusive designs that ruin their aesthetic. There are other complications, too; an early dotted prototype created an optical illusion that caused intense feelings of nausea and vertigo in the office workers unfortunate enough to look out the window.

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New designs, however, avoid these pitfalls and capitalize on birds’ ability to perceive light on the ultraviolet spectrum; while humans can barely tell the difference, birds see a bright, iridescent warning to stay away. At least, that’s the hope—Mesure says some studies indicate it might actually be a bright, iridescent invitation to fly into a window.

It also may be possible that birds themselves will eventually adapt their migration patterns, since both the urge to migrate and the direction a bird goes are hereditary. The blackcap, for example, used to visit the United Kingdom briefly on its way to feed in southern Spain. Increasingly, however, they spend whole winters in Britain, luxuriating in backyard birdfeeders and the heat generated by cities. One subspecies of white-crowned sparrow gave up migrating from California to Alaska and northwestern Canada altogether.

Overall, however, Stutchbury is not optimistic. “You’re putting such a huge pressure on natural populations,” she says. “It’s a bit naïve to think that they’ll be able to evolve their way out of the problem.” And although it appears that full-time city residents such as pigeons can learn and adapt to new habitats—they rarely fly into windows—migratory birds continue to die from collisions despite previous successful trips through city environments.

On Toronto’s streets, Mesure points out some of the towers that have taken steps to mitigate bird collisions: a tight cluster of grey dots on a window, a series of horizontal bars made to look like venetian blinds. But between the light pollution and the thousands of brightly reflective buildings, he fears it’s not enough. Not many people are willing to make the effort to turn off their lights or sacrifice the aesthetic of their homes and offices. “It’s just so…” he pauses, frustrated. “People are so attracted to the shininess of it all.”

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Evidently, it’s a problem we share with the birds.

Alex Tesar is a reporter for The Walrus.

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