Conservation news

Window tech could save billions of birds, and it’s already here

  • Close to one billion birds in the United States die each year from collisions with windows on buildings.
  • Last year, a 48-year study reported that the overall bird population in the U.S. has declined by roughly 30% since 1970 in the United States.
  • A variety of methods to prevent bird collisions could reduce these numbers, including the use of ultraviolet signature coatings on glass.
  • Combining this technology with sustainable window solutions that control interior light and heat may make it easier for building owners to adopt bird-friendly materials.

This may sound familiar: you’re sitting at home, absorbed in your daily activities, when THUD; a bird crashes into your window. You jump, or at least look up, and feel a moment of concern: “I hope it’s okay!” After inspecting the smudge on the glass, your next thought might be, “Well, there’s nothing I can do now — at least it was only one bird.”

It turns out, “only one bird” is a pretty common occurrence. A recent study estimates that nearly a billion birds are killed annually from hitting windows — and that’s just in the U.S. No one knows how many die worldwide, but it would certainly be in the billions. And the impact of these losses may go well beyond just the birds involved.

“People have no idea the ecological services that birds provide,” says Christine Sheppard, the bird collisions campaign manager at the American Bird Conservancy (ABC). She says birds play a crucial role in strengthening habitats against climate change, and helping ecosystems bounce back after disaster hits. “California burns down, and birds bring seed back in so habitats can regenerate,” she says.

While simple solutions to bird collisions have existed for a while, newer window technology may make it easier for companies and individuals alike to adopt bird-safe solutions while also lowering energy costs and carbon emissions.

How bad is one billion dead birds?

By some estimates, these one billion deaths may account for 5 to 10% of the total U.S. bird population annually (estimated at 10 billion to 20 billion), making window collisions one of the biggest killers of birds. But assessing the severity of an issue like this can be difficult, especially when the number of birds in the U.S. drastically fluctuates each year due to migration, according to Sheppard.

Matthew Kamm, a biologist and educator with Zoo New England, says migratory birds are often hit the hardest, especially the warblers. Hummingbirds and swifts, also migratory species, showed the highest risk among birds included in the report. The report also found that seven species that are among the most vulnerable are also listed nationally as “birds of conservation concern” by the US Fish and Wildlife Service and 10 of these most vulnerable species are listed regionally.

While window collisions are not the sole cause of population decline for these struggling species, Sheppard says they can be detrimental to the already massive effort it takes for birds to re-establish healthy numbers.

Hummingbird killed after strike with window. Image by beard14 via CCSearch CC BY-NC-SA 2.0

“If you don’t worry about birds until they’re at the point of extinction, it’s phenomenally difficult to try to get them back,” she says, explaining that well before a bird is gone, its ecosystem begins to lose the critical services that it provides. This makes it even more difficult for birds to rebound in their changed environment.

“The simple fact is, being a long distance migrant in the modern world is just harder than it used to be,” Kamm says.

Before migratory birds even begin their journeys, increasingly unpredictable weather patterns caused by climate change can throw off their schedules. Once in the air, urban developments not only heighten the potential for building collisions, but also provide confusing light pollution at night and contribute to the loss of green spaces and insect prey that birds require to rest and recharge.

“They’re more vulnerable to predators when they get to where they are going,” Kamm says. “It’s really a death from a thousand cuts.”

The only two threats graver than window collisions are critical habitat loss and predation by domesticated cats, an invasive and predatory species. All these hazards have added up over the past 50 years. According to a study in Science this past year, 2.9 billion birds have disappeared in the United States since 1970, an estimated loss of about 30% of the population.

Stats like this can be a canary in the coal mine for ecosystem integrity, predicting more dramatic disappearances to come.

“Extinction begins with loss in abundance of individuals that can result in compositional and functional changes of ecosystems,” write the scientists behind the Science study that showed nearly 3 billion in losses.

Potential solutions

But bird deaths by collisions can be mitigated, according to the ABC, by a number of potential solutions. Some of these include easy do-it-yourself methods such as tempera paint and stick-on window decals. They also rate bird-safe products using tunnel tests, in which scientists measure how many birds fly toward a tunnel exit covered in clear glass versus the sample product.

One type of solution that ABC approves is glass with “ultraviolet signatures,” which allow UV light to reflect off the outside of the window. Since most birds can see in ultraviolet, glass that reflects ultraviolet light sends the message that the space is occupied rather than an open patch of sky. For humans, the window remains transparent.

What birds see, left, compared to what humans see looking through UV signature-coated glass. Image courtesy of Arnold Glas Corp.

Although Sheppard is encouraged by technology like this, she says it still has its flaws. For example, not all birds can see in the UV range, and levels of UV light vary from place to place and throughout the course of the day.

“I’m guessing that UV signatures are going to work a whole lot better in Phoenix, than in a place like Portland,” she says.

Despite the flaws, Kamm says he thinks there is still a healthy demand for these solutions.

“I feel like [bird-safe materials] should be an easier sell than, you know, some other environmental asks,” he says.

Michael Reed, a professor at Tufts University specializing in avian ecology and conservation biology, stresses the importance of including bird-safe solutions in the conversation about sustainability in the first place, and says that everyone has their own perspective of what sustainable means.

“Sustainability [reflects] what gets paid attention to as a social issue,” he says. “If people get behind [bird-safe solutions], that’s what will be the focus. But if no one talks about it, no one cares about it, then it’ll never rise to the top.”

This is especially true for big companies and institutions: if bird-safe glass costs more than standard windows, companies will likely opt for the cheaper option. But to Reed, that demonstrates an opportunity.

“If enough people raise a fuss,” he says, “then politicians listen and laws get passed that require companies to do something. I’m not sure the company would actually care, but they would do something about it, and as far as I’m concerned that might be sufficient.”

Luckily for birds, social pressure may not be the only way to incentivize companies and individuals alike to start using safer materials.

Several manufacturers provide bird-friendly UV signature glass in tandem with technology that regulates how much heat and light can pass through. Glass coatings such as Bird1st from Guardian Glass and ORNILUX from Arnold Glas add UV-reflecting stripes or patterns, and can be paired with low-emissivity (heat-filtering) and solar-control treatments. This combination allows windows to both maintain the temperatures inside the building and mitigate the number of bird collisions outside.

Like transition eyeglass lenses, dynamic glass self-tints in reaction to the amount of sunlight it is exposed to throughout the day. It can also adapt to artificial light coming from within, which does birds a bonus favor by lowering light pollution that can confuse migratory birds at night.

Unidentified bird looking at window. Image by guppiecat via CCSearch CC BY-NC-ND 2.0

Controlling the internal climate can be attractive to building owners not only because it creates a comfortable space, but also because it reduces energy costs, helps earn LEED credit points, and can reduce greenhouse gas emissions.

“It’s relatively straightforward to get people to consider birds during the design phase,” Sheppard says. “It shouldn’t add any cost to the building if you’re making this set of decisions as opposed to that set of decisions, because there’s a lot of overlap between bird-friendly glass and different ways to control heat and light and sometimes even security.”

Beyond UV window technology, people are continuously looking for novel approaches to preventing collisions. One group is looking to develop nanomaterials that create signals birds can respond to and avoid, according to Sheppard. Another is working on sound nets that divert birds from an area using noise. While the actual implementation of these products may be tricky, new technologies like these could save birds from dangerous and undesirable areas, like airports.

For Sheppard, no matter the method, saving birds from collisions ultimately comes down to including them in the environmental agenda, and pushing for action.

“There are very few conservation issues where you can get information in the morning and do something about it in the afternoon,” she says. “Usually, it’s just depressing. But this is actually something almost anybody can do something about. We know what to do, we’ve just got to get everybody to do it.”


Banner image: The imprint left by a bird after colliding with a window. Image by Bill Gracey via Flickr (CC BY-NC-ND 2.0).


Loss, S. R., Will, T., Loss, S. S., & Marra, P. P. (2014). Bird–building collisions in the United States: Estimates of annual mortality and species vulnerability. The Condor116(1), 8-23. doi:10.1650/condor-13-090.1

Rosenberg, K. V., Dokter, A. M., Blancher, P. J., Sauer, J. R., Smith, A. C., Smith, P. A., … Marra, P. P. (2019). Decline of the North American avifauna. Science366(6461), 120-124. doi:10.1126/science.aaw1313