take a guess: how many birds die from hitting windows in the u.s. every year? 

brace yourself, because the answer might be surprising: 1.28 to 3.46 billion every year at a minimum, according to ornithologists. conservatively, that’s around 3.5 million birds dying each and every day around the country from running headfirst into windows. these collisions are a key factor contributing to the net loss of 29% of america’s bird population since 1970.

but unlike other complex challenges facing birds, such as habitat loss and climate change, the window collision problem is a simple one. researchers have developed affordable, straightforward methods that can be applied to windows to protect birds — now, experts say it’s up to us to implement them.

listen to the audio story below to learn more about why these collisions happen, why they’re a problem and how people can help prevent them.

audio story transcript

[scoring intro]

madeline shaw: catherine quayle is on a walk in her brooklyn heights neighborhood when she comes face to face with a tiny tragedy. [pause] she looks down and sees a small bird… 

catherine quayle: it’s lying there as if it were sleeping against this apartment. 

ms: but it isn’t sleeping, it’s dead. it appears to have run headfirst into a window. [pause] this wasn’t just any bird either, but a yellow-bellied sapsucker. picture a small black and white speckled woodpecker with a red cap and a buttery tint to its chest. [yellow-bellied sapsucker sound effect] like their name suggests, these birds live on sugary tree sap. but that’s not the only thing that makes them special to catherine. 

cq: they’re just really cool. you know, not a lot of woodpeckers migrate. there’s only a few species, and this is one species that does migrate.

ms: this bird had likely started life with a handful of siblings, nestled together in a tree’s heartwood inside a northern forest. it had spent its days foraging for food and avoiding predators before beginning a long journey south, away from the nest.

cq: it’s so sad that this beautiful bird has gone through everything it had to go through to reach maturity, to start its migration—already the odds are against birds in that situation—and then to come and just die against someone’s apartment window. what a travesty. what a travesty.

ms: for this bird, migration came to an untimely end on a new york city sidewalk. [pause] [scoring starts] but this wasn’t a one-time accident. it’s happening every day, in new york city and around the world, over and over and over. to make matters worse, these deaths are coming at a time when birds are already facing lots of complex challenges, from habitat loss to bird flu. [scoring intensifies]

ms: my name is madeline shaw, and today on scienceline we’re going to talk about the window collision crisis — why it happens, why it’s so deadly, and simple solutions that could help our feathered friends.

ms: first, we need to understand the scope of the problem. just how many birds die from hitting windows in the us each year? i went to the streets of new york to see what people think.

[vox pop guesses – 100k, 5 million, 100 million, etc.] [scoring ends]

ms: no one even came close. the real number?

daniel klem: that figure turns out to be 1.26 to 3.46 billion every year in the united states alone. 

ms: that’s right, billion with a b, every year. this is dr. daniel klem. he’s an ornithologist who has spent more than 50 years studying the deadly effects of glass windows on birds.

dk: an easy way to think about that is that it’s 3.5 million birds every day, 365 days a year. i just don’t think the general public, and frankly, most of the scientific community is really aware of the mortality and its level and its influence on the health of the bird populations of north america.

ms: so why is this happening? 

dk: they just don’t see it. it’s like if you look at a reflective window, you’re seeing the facing habitat in the sky. and that’s an illusion, for sure, but the bird doesn’t recognize that as an illusion. they recognize it as an actual scene, which they try to reach.

ms: now there are lots of windows in new york, especially on newer skyscrapers. but daniel told me this problem goes way beyond cities. 

dk: it’s happening everywhere. most of the deaths are happening at residential homes, or homes that are, you know, one to three stories high.

ms: now you might be thinking, “but i’ve never seen a bird hit my window.” you think you’d notice if your windows were killing multiple birds a year, right? daniel says not so fast. when someone says that to him, he asks if he can come by and take a look himself.

dk: there’s never been a home where i haven’t found evidence that birds have struck windows. skeletons, feathers, feather smudges, blood, sometimes, seeds that have been ejected by the bird that hit, fecal material on the glass surface. all of these are evidence. they’re just unaware of it. they might hear a little knock, or may think it’s a dropping of a spoon or something like that, but it’s some bird that has hit their window. 

ms: and on top of that, if a bird hits your window, there might be no signs at all. researchers have found that anywhere between 50 to 90 percentof all bird strikes leave no evidence.

ms: after decades studying the problem and working on solutions, daniel says addressing the threat posed by windows is now urgent.

dk: from 1970 up to the present, 29% of all the birds in north americahave been lost, and windows, among other tragedies, are part of that. 

ms: so, what can be done to keep birds out of harm’s way? [more hopeful scoring] turns out the solutions are actually pretty easy. i talked about them with katherine chen, a conservation biologist who runs project safe flight for the nyc bird alliance. for almost 30 years, project safe flight has tracked window collision deaths in the city and advocated for more bird-friendly building design.

katherine chen: to make glass bird safe, all you have to do is put something on the glass or in front of the glass that helps the birds realize, hey, you can’t actually fly through this. the golden rule is using two inches by two inches spacing. 

ms: essentially, by putting a pattern on the outside of your window, you can signal to a bird that there’s an obstacle in the way. this 2×2 pattern is important, because it helps prevent even the smallest birds from thinking they might be able to squeeze through. you can purchase stickers or tape for example, that are specially designed to protect birds. but katherine says there are plenty of other options too. 

kc: it doesn’t have to be anything expensive. you can get creative with it. you can use tempura paint to draw fun patterns.

ms: there’s proof this strategy works, right here in new york.

kc: a really iconic example is the javits center. they used to be this building that had a lot of mirrored glass. it was really dangerous for birds. they voluntarily chose to renovate their building and use bird safe glass to replace all of that old mirror glass, and it was super successful.

ms: these changes reduced the number of collisions by at least 90%at the javits center. now imagine if these improvements were made across the city. in fact, katherine says that contacting local elected officials to advocate for bird-safe legislation could help usher in more positive change. 

kc: we do have a local law here in new york city, local law 15of 2020, and it mandates all new construction in the city as well as any buildings are going to be replacing all of their external glazing to use bird safe materials on their building. that was a big win for new york city’s birds, and it is the most comprehensive bird safe buildings law in the country.

ms: new york state is also considering proposals that would require bird-safe glass in buildings owned or used by the government. [pause] but as long as windows remain a danger to birds, there will be more tiny collision victims in need of saving. 

ms: that’s a job for people like catherine, who found the yellow-bellied sapsucker. she works at the wild bird fund—one of the few wildlife rehabilitation centers in new york city. she says the clinic sees about 1500 birds a year that have been seriously injured from flying into a window. they do what they can to help these patients, but…

cq: there’s not a lot of complicated intervention that’s possible, especially since many of these birds are tiny little four gram birds. you know, you’re not going to splint a wing, you’re not going to do any kind of surgery on them. it’s really kind of a waiting game.

ms: instead, they give the birds anti-inflammatory medicines, clean their wounds, and let them rest. in the end, about 6 in 10 of the birds that arrive don’t make it. 

cq: if you see one bird, you think, oh, that’s sad. but you know, imagine seeing 30 or 40 of them every day. it’s heartbreaking. 

ms: still, catherine takes comfort in the survivors.

cq: it’s very rewarding when we get to release them, and we do have some really nice opportunities to set these beautiful birds free in the park and see them return on their migratory paths.

ms: each little rehabilitated bird is a victory, because as daniel says,

dk: we have to be in a position to protect the common birds while they’re still common, and we don’t have any choice about the endangered species. we have the solutions. we just have to enact them. [pause] what kind of world would we live in if it didn’t have birds in it? 

ms: i’m madeline shaw, and this has been scienceline. this episode was written, edited and produced by me, with help from blythe terrell. music by blue dot sessions and sound effects courtesy of the bbc sound effects library. many thanks to catherine quayle of the wild bird fund, dr. daniel klem of muhlenberg college, and katherine chen from the nyc bird alliance for sharing their thoughts. and thank you for tuning in.

[bird sounds, outro scoring]