how many birds fly into windows

For birds, glass windows are worse than invisible. By reflecting foliage or sky, they look like inviting places to fly into. And because the sheer number of windows is so great, their toll on birds is huge. Up to about 1 billion birds die from window strikes in the U.S. each year, according to a 2014 study.

The good news is that you can greatly reduce the danger your home’s windows pose to birds with some simple remedies, according to Christine Sheppard, who directs the Bird Collisions Program of the American Bird Conservancy. The group offers extensive information on preventing collisions on its website. The Fatal Light Awareness Program also offers great information on preventing bird collisions.

What happens to birds that hit windows? Sadly, the bird often dies, even when it is only temporarily stunned and manages to fly away. Many times these birds die later from internal bleeding or bruising, especially on the brain. Daniel Klem of Muhlenberg College has researched this issue since the 1970s. He writes, “Glass is an indiscriminate killer that takes the fit as well as the unfit of a species’ population.”

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Every year in the United States, a great number of birds are killed by glass collisions. However, the majority of Americans are unaware of this risk, and even fewer are aware of the easy and affordable fixes that can be used to help stop these deaths.

In order to clarify this ubiquitous danger, ABC’s collision specialists, Christine Sheppard, Ph. D. , and Bryan Lenz, Ph. D. assemble a list of answers to the top 15 questions they get asked. Take a look. Chances are, weve got an answer for you below.

how many birds fly into windows

Although it is challenging to provide a conclusive response due to the widespread use of glass, Smithsonian researchers made an effort in 2014.

They calculated that dwellings and other structures with one to three stories were responsible for approximately 253 million bird deaths a year, or 44% of all bird fatalities. Larger, lower-rise structures with four to eleven stories contributed to 339 million deaths. And each year, 508,000 birds are killed by high-rise buildings with eleven stories or more. Because there are fewer skyscrapers overall, fewer birds are killed by them even though individual skyscrapers can be quite lethal.

Combining these figures, the Smithsonian concluded that, with a median estimate of 599 million, collisions probably kill between 365 million and 1 billion birds yearly in the United States.

For a number of reasons, we think the actual figure is closer to one billion or even higher. One reason is that the study’s data was collected more than ten years ago, and since then, glass use has steadily increased, raising the risk of deadly collisions. Furthermore, we now know that reports of bird carcasses frequently understate the number of deaths (refer to questions 4 and 5). This implies that a greater number of dead birds remain uncounted than previously believed.

This indicates that domestic cats are the only anthropogenic (caused by humans) threat that kills more birds in the United States annually2.

Both humans and birds cannot see transparent glass, but most of the time, humans can anticipate the presence of glass and avoid collisions by using visual cues such as door frames. Birds, of course, dont share this ability. Because they interpret reflections as actual objects, they can cause collisions when they present glass reflections, particularly when they represent food, shelter, or an escape route. Learn more by visiting our “Why Birds Hit Glass” page.

how many birds fly into windows

Some birds may be lucky enough to be momentarily stunned and escape permanent injury after colliding with glass, but this is not always the case.

Birds sustain internal bleeding, concussions, or harm to their bills, wings, eyes, or skulls in many of these incidents3. Birds with even minor injuries are far more susceptible to predators and other environmental threats, even though they might be able to fly for a short while.

However, in many cases, birds are killed right away and never escape.

For a variety of reasons, collisions at residential and commercial buildings frequently go unreported. First off, a lot of birds that strike windows do not always die instantly and depart without leaving a trace.

According to one study, only two of the 29 birds that collided with windows died right away, leaving a carcass at the base of the window4. However, even birds that initially fly away most likely die somewhere else due to severe injuries like fractured bones and beaks, concussions, and internal bleeding3.

Second, animal scavengers frequently remove bird carcasses from the base of buildings quickly when they do die. For a simple meal, cats, raccoons, raptors, and even squirrels can learn to wait at windows where collisions happen.

In addition, birds can tumble through grates, land in landscaping, fall onto inaccessible rooftops, or land in dense vegetation that obscures their view.

The total number of dead birds discovered is consistently much lower than the actual number of birds that collided with the glass, even in the case of extensive collision monitoring programs. This is the case for similar reasons to the response given above.

A large number of birds that strike windows do not instantly perish and depart without leaving any evidence behind. According to one study, only two of the 29 birds that collided with windows died right away, leaving a carcass at the base of the window. But birds can get serious injuries3, so even if they take off at first, they might end up dead somewhere else.

Second, when birds do pass away and land on the ground, the carcasses are usually removed by animal scavengers and humans—often facilities teams—before monitors can discover them. Collision monitors even report that animals, like squirrels and gulls, have learned to wait at windows where collisions happen in order to have a quick meal. Because of the severity of this issue, academic monitoring programs carry out “carcass persistence studies” to determine how many dead birds are removed before monitors walk their routes and discover them5,6,

Researchers have discovered that the rate at which injured and dead birds vanish varies greatly from site to site7; in some instances, carcasses are removed in a matter of hours8, while in others, it takes days5,6, 7. At certain locations in New York City, for instance, only 25% of the carcasses placed on collision monitoring routes remained after the collisions and the monitors walked their routes later that same morning.

Lastly, not all of the remaining birds are always picked up by monitors9. Birds can fall through grates, onto inaccessible rooftops, into landscaping, into thick vegetation that obscures their view, get swept away in gutters, or simply go unnoticed because they blend in with the surroundings.

In one study where the researchers took into account both scavenging and imperfect detection, they calculated that only roughly 2020% of the killed birds were actually found by people who were looking for them. Therefore, it is safe to conclude that the number of birds detected during a monitoring effort, particularly if it is not thorough, will be a small portion of the birds that truly perished and a much smaller portion of the total number of birds that struck the windows.

There are many ways to making windows bird-friendly. One of the best is to use external insect screens. These screens almost completely block reflections, and in the unlikely event that birds do strike them, the impact is softened, minimizing damage. Easy installation of these screens on new or old home windows is an additional advantage.

If screens aren’t an option, you can make window patterns that birds will perceive as solid objects that need to be avoided using a variety of materials, including tape, decals, strings, cords, paint, netting, and shutters. Check out our great home-friendly solutions guide here.

Make sure to remove any gaps larger than two inches so that birds cannot see a feasible path between the markers or objects you are using.

Always keep in mind that the material you choose must be visible to birds from a minimum of ten feet away, giving them enough time to notice it and alter their course.

how many birds fly into windows

Applying solutions outside the window, where they are readily visible, is the best option.

However, using external solutions isnt always an option. Certain windows, such as those found in tall buildings, can be challenging to reach from the outside.

In these cases, we recommend testing a variety of solutions. This is due to the fact that different types of glass have differing degrees of reflection, and sadly, there isn’t a universal fix.

Apply a sticky note, piece of tape, or a sample of your suggested solution to the inside of the window and observe it from the outside every hour or two, beginning in the early morning, to conduct a test.

Birds will see your test material if you can see it most of the time, so you might be able to solve the problem internally.

However, internal solutions frequently fail, and reflections will obscure your solution for some or all of the day, diminishing or eliminating its efficacy.

But this shouldnt deter you from acting. is better than doing nothing. Adding something to your windows is better than doing nothing.

how many birds fly into windows

No, you can save birds without sacrificing your vision.

There exist efficacious solutions that occupy as little as 1% of the window area, permitting sunlight to enter and a gaze out. According to our observations, people get used to bird-friendly design solutions quickly and frequently forget they are there. Additionally, we’ve discovered that when loved ones, acquaintances, or clients see the pattern and understand its significance, they value the efforts made to preserve birds.

Depending on your preferences, there are several options available if you’re looking to retrofit existing windows.

When planning a new construction or replacing windows, take into account the expert solutions that architects recommend. Architects have long favored many of these sophisticated products purely for their visual appeal. To learn more about window replacement or building design, go to the “Architects, Planners, and Developers” page. Looking for inspiration? Check out our bird-friendly building gallery.

how many birds fly into windows

Light can increase collision numbers in several ways. According to recent studies, birds are drawn to the human-built environment by urban glow, increasing the likelihood of collisions10,11.

Strong lights set against the night sky also draw migratory birds that are flying at night. The phenomenon referred to as the “beacon effect” can be attributed to various factors such as lighthouses, offshore oil platforms, or intense light displays, such as the twin beams at the 9/11 Tribute in Lights memorial located in New York City. These lights have the potential to seriously impair birds’ ability to navigate, causing them to veer off course and become trapped near the light12 or confused. Volunteers at the 9/11 memorial keep an eye on the birds, and when necessary, they turn out the lights to ensure everyone can pass safely.

Brightly lit building facades can also affect birds. These facades and their vivid windows may occasionally result in nighttime collisions13, 14. These birds can be observed flapping at windows that are lit or worn out on the ground, where they are more susceptible to predators.

Even though nighttime lights can be dangerous, it’s crucial to remember that most collisions happen during the day. These collisions, which are frequently fatal and direct, are caused by habitat reflections in or seen through glass.

While turning off lights is a great way to support birds and other wildlife, treating your windows with one of the many available options is the best way to prevent collisions, especially at homes.

how many birds fly into windows

For a bird, a glass door is just another obstacle to fly around, but a single decal might be sufficient to alert a vigilant human to its presence.

Decals and other collision deterrents must be placed with appropriate spacing to give the impression of a cluttered environment through which it would be difficult or impossible for birds to fly in order to effectively deter birds. You can learn more here. It’s important to keep in mind that no pattern you choose for your windows should have any gaps wider than two inches.

The first thing to do is document the problem. When you come across dead birds, take pictures of them and record the numbers and dates.

Ask the facilities or maintenance department what they have observed; they are typically in charge of cleaning up dead birds that have struck glass, and they could be valuable allies in helping you gather information or persuade building managers of the threat to birds.

Once the issue has been documented, go over the window solutions on ABC’s website, get in touch with the building manager or owner to inform them of the problem, and offer guidance or resources (like this blog) on how to resolve it.

Remember that you are asking for help and seeking a partner in order to save birds, so make sure that these exchanges are constructive and non-aggressive. Refrain from demonizing the person in charge of a collision issue that they probably were unaware of.

You can also find out if anyone else is concerned about the same things by speaking with residents, employees, or shoppers in the disputed building. If so, inquire as to whether they would like to participate. Collaborating with others creates a collective voice that can raise the issue’s profile.

Remember, there are many ways to get involved. These consist of lending a hand with monitoring, composing correspondence for building owners, participating in building management meetings, and planning community outreach.

Visit our “How to Advocate for Retrofits” page for additional advice.

how many birds fly into windows

Structures not built with bird-friendly design principles run the risk of becoming lethal to birds.

The amount of glass used, where it is placed, how reflective it is, how tall and how much vegetation surrounds the building, and whether or not there is water are some of the variables that affect how dangerous they are.

We feel that all new construction, not just glass-covered skyscrapers, should include bird-friendly features due to the increased cost of creating a bird-friendly building. When considering these features at the outset of the planning process, the cost is lower than when retrofitting an existing building.

There are several ways to help make this happen. The first step is to create and approve a local ordinance mandating that your community adopt bird-friendly building standards. To download an easy-to-use ordinance template, click here. You can also review our list of current ordinances that require bird-friendly design or establish voluntary guidelines.

Remember that most ordinances only apply to large buildings, leaving out homes and low-rises, so it’s critical to ensure that the ordinance covers the greatest number of buildings.

While enacting an ordinance is a fantastic achievement, there are other things you can do.

Think about voicing your concerns to the developers of both proposed and ongoing construction projects. We advise concentrating on projects with a high chance of success because this can be a time-consuming process (e g. , museums, nature centers) or establishments that have an impact on several structures (e g. , local government, academic institutions, healthcare facilities, and architectural firms) to assist them in implementing building regulations that protect birds.

Though it’s important to ensure that new construction has bird-friendly designs, keep in mind that hundreds of millions of birds already perish each year due to existing buildings. Thus, for the foreseeable future, retrofitting homes and other buildings will be necessary to reduce bird collisions.

To learn more visit our “Creating Bird-Friendly Legislation” page.

how many birds fly into windows

Not necessarily. When architects, developers, and other stakeholders intend to create a LEED-rated building, they review available credit options and select the amount of credits needed for the rating they want.

Bird-friendly credits, however, werent available until 2011, when the LEED program adopted a new, bird-focused building design credit known as “Pilot credit SSpc55: Bird Collision Deterrence.” LEED added a permanent “Bird Collision Deterrence” credit to the Innovation Catalogue in 2022.

Utilizing this bird-friendly credit is optional, just like with all other credits in the LEED system. Thus, not all LEED-rated buildings are bird-friendly, even though many builders have chosen to use this credit.

We strongly advise architects and builders to incorporate bird-friendly building guidelines into their designs, regardless of their LEED rating. Check out our LEED Innovation Credit page for additional information regarding testing and LEED ratings.

No two collisions occur at the same rate over a year or even a single day.

The majority of collisions occur during the day or right before dawn, though some do happen at night. Particularly in the mornings, collisions tend to occur more frequently during the day15,16,17, and 18. This occurs during migration when migratory birds stop to look for a place to land and refuel after flying all night. People who land in or close to cities discover themselves in a deadly glass maze. Furthermore, local birds are usually busiest in the morning when they wake up hungry and start looking for food.

Over the course of a year, migration periods frequently result in the highest increases in collisions as large numbers of birds pause to rest, frequently in uncharted territory where glass is prevalent10,19,20. Numerous collision programs concentrate on collisions that happen during migration in urban areas where they typically happen in large numbers. Fall typically sees higher migrant mortality than spring because there are more birds in the air during that season. This is due to the fact that fall migration consists of both mature and summer-born juvenile birds. Spring migration includes only adults returning to breed.

But migration is not the only dangerous season. Moreover, we observe an increase in collisions in the late spring (18) when nesting birds fledge their young, and in the winter (21, 22), when resident birds abandon their territories and travel farther in pursuit of food. Bird feeders near windows can result in collision deaths during the winter23.

how many birds fly into windows

The American Bird Conservancy works to minimize bird-glass collisions by creating an environment where human construction has left birds as safe as possible. To maximize our impact, we focus on the following areas:

Product testing: To better understand how birds interact with different commercially available window treatments, we run a flight tunnel (watch our video to learn more) These assessments enable us to develop guidelines for architects designing bird-friendly buildings and suggest practical fixes for occupants of houses and other structures. We assess and record scientific literature about bird collisions as subject matter experts.

Codes, laws, and LEED: We support the development of science-based, bird-friendly codes based on our own and other researchers’ tunnel test results. For instance, we collaborated with Congressmen to draft the national Bird-Safe Buildings Act, which mandates the use of bird-friendly building materials and designs in public buildings. Additionally, we have assisted in passing local ordinances and establishing building guidelines such as the LEED Bird Collision Deterrence Innovation Credit. For more information, visit our Legislation page and look under the Bird-friendly Legislation tab.

Teaching engineers and architects: The American Institute of Architects and the Green Building Council both offer continuing education credits to architects who complete ABC’s bird-friendly building design course.

Advice on retrofits and monitoring: ABC assists companies, academic institutions, and private citizens in developing efficient monitoring systems and choosing the best ways to lower the number of collisions. Public outreach and education: Increasing public awareness of this issue is a major component of ABC’s collisions mission. We link people to solutions and give legislators, architects, engineers, and homeowners comprehensive information.

New projects: We are constantly striving to enhance window goods that are friendly to birds while promoting public action to lower bird mortality rates. You can follow us on Facebook or X (formerly Twitter) or sign up to receive email updates about our collisions program.

Dr. Christine Sheppard is ABCs Bird Collisions Campaign Director. She earned her Ph. D. before joining ABC, he was employed at Cornell University as the head of the ornithology department at the Bronx Zoo. Since then, she has written the books for Bird-friendly Building Design in both of its editions published by ABC. She developed AIA/LEED continuing education courses on bird-friendly design, contributed to the creation of San Francisco’s standards for bird-safe buildings, and has written laws and codes in numerous jurisdictions. Sheppard was involved in creating LEED Pilot Credit 55: Reducing Bird Mortality for the USGBC. Because of her work on glass testing, she was named one of Engineering News-Record’s “Top 25 Newsmakers for 2014.” She has collaborated with most major glass manufacturers on the design and assessment of materials that are friendly to birds.

Dr. Bryan Lenz is ABCs Bird Collisions Campaign Manager. He earned his Ph. D. at Tulane University and held positions as Chief Scientist at the Western Great Lakes Bird Observatory and Director of the Community Conservation Program in Bird City, Wisconsin. Bryan works at ABC to lessen the risk of bird collisions caused by the built environment, particularly by glass. Research, design, law, building codes, outreach, education, and marketing are all incorporated into his work.

  • Loss, Scott R. , Tom Will, Sara S. Loss and Peter P. Marra. 2014. The annual mortality and species vulnerability estimates of bird-building collisions in the United States Condor 116:8-23. https://doi. org/10. 1650/CONDOR-13-090. 1.
  • Loss S. R. , Will T. , and Marra P. P. 2013. The effects of domestic cats kept in freedom on American wildlife Nature communications 4(1):1-8. https://doi. org/10. 1038/ncomms2380.
  • Klem, D. , Jr. 1990. Bird injuries, reasons for death, and recovery following window collisions Journal of Field Ornithology 61(1):115- 119. https://www. jstor. org/stable/4513511.
  • Samuels B, Fenton B, Fernández-Juricic E, & MacDougall-Shackleton SA. 2022. Viewing the “black box” of bird-window collisions: passively captured home backyard videos PeerJ 10:e14604 https://doi. org/10. 7717/peerj. 14604.
  • Kummer, J. A. , C. J. Nordell, T. M. Berry, C. V. Collins, C. R. L. Tse, and E. Bayne. 2016. Bird-window collision estimates are modified by urban scavengers using the removal of bird carcasses. Avian Conservation and Ecology 11(2):12. http://dx. doi. org/10. 5751/ACE-00927-110212.
  • Riding, Corey S. and Scott R. Loss. 2018. Factors affecting observer detection and experimental estimation of scavenger removal in surveys of bird-window collisions Ecological Applications 28(8): 2119-2129. https://doi. org/10. 1002/eap. 1800.
  • Hager, Stephen B. , Bradley J. Cosentino and Kelly J. McKay. 2012. The scavenging behavior of bird carcasses left behind by window collisions in an urban environment J. Field Ornithol. 83(2) 203-211. https://doi. org/10. 1111/j. 1557-9263. 2012. 00370. x.
  • Parkins, Kaitlyn L, Susan B. Elbin and Elle Barnes, 2015. Light, glass, and bird–building collisions in an urban park. Northeastern Naturalist 22(1): 84- 94. http://dx. doi. org/10. 1656/045. 022. 0113.
  • Bracey, Matthew A. Etterson, Gerald J. Niemi, and Richard F. Green. 2016. Variation in the mortality and scavenging rates of birds colliding with windows in an urban environment The Wilson Journal of Ornithology 128(2):355- 367. https://doi. org/10. 1676/wils-128-02-355-367. 1.
  • Fink D, Buler JJ, La Sorte FA, Farnsworth A, and Cabrera-Cruz SA 2017. Seasonal correlations between nocturnally migrating bird populations and urban light pollution Glob Change Biol. 23:4609–4619. https://doi. org/10. 1111/gcb. 13792.
  • McLaren, J. D. , Buler, J. J. , Schreckengost, T. , Smolinsky, J. A. , Boone, M. , Emiel van Loon, E. , Dawson, D. K. and Walters, E. L. 2018. Artificial light at night confuses migratory birds’ broad use of their habitat. Ecol Lett. 21(3):356-364. https://doi. org/10. 1111/ele. 12902.
  • Van Doren, Benjamin M. , Kyle G. Horton, Adriaan M. Dokter, Holger Klinck, Susan B. Elbin and Andrew Farnsworth. 2017. High-intensity urban light installation dramatically alters nocturnal bird migration. Proc Nat Acad Sci: 114 (42) 11175–11180. https://doi. org/10. 1073/pnas. 170857411.
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  • Gelb, Y. and N. Delacretaz. 2006. Avian window strike mortality at an urban office building. Kingbird 56(3):190-198. https://nybirds. org/KBsearch/y2006v56n3/y2006v56n3p190-198gelb. pdf.
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Why Birds Collide With Windows

how many birds fly into windows

Daytime and nighttime window collisions are the two primary categories. Birds collide with windows during the daytime because they can see vegetation or potted plants on the other side of the glass, or they can see reflections of the vegetation. Most songbirds and other nocturnal migrants crash at night when they fly into illuminated windows.

For reasons not entirely understood, lights divert nocturnal migrants from their original path, especially in low-ceiling or foggy conditions. In the lighted area, they mill about, sometimes colliding with one another or the lighted structure. As a subsequent hazard, migrants drawn off course by urban lighting may roost safely nearby, only to become vulnerable to daytime reflections in windows the following day. The BirdCast project and the Fatal Light Awareness Program have more about this problem.

One more reason is that birds occasionally target their reflections in windows. When territoriality is high in the spring, this occurs most frequently. Despite the fact that it may irritate the homeowner, the bird’s survival is rarely in danger. The majority of the solutions listed below for window strikes also address the issue of birds attacking reflections.

Treatments for Existing Windows

Ideally, vertical markings on windows should be arranged in a 2-by-2-inch grid to discourage small birds. (This will protect the windows from even the tiniest birds, like kinglets, siskins, hummingbirds, and gnatcatchers.) ) The exterior of the window should be marked using all marking methods.

  • Tempera paint or soap. Use tempera paint or soap to leave a lasting, low-cost mark on the outside of the window. You can paint designs or other artwork on your window, or you can use the 2 by 2 inch grid pattern shown above.
  • Decals. Apply stickers, decals, sun catchers, masking tape, mylar strips, and other items—even sticky notes—to the window’s exterior. These are only effective when spaced very closely (see above). Note that hawk silhouettes do little to deter birds. Recall that adding a few window stickers to a large window won’t stop collisions; instead, the stickers must cover the majority of the glass, leaving gaps that are too small for birds to fly through.
  • Dot Patterns and Tape. Durable tape products make it simpler to apply the proper dot spacing throughout your window. Items like those found at Feather Friendly are effective in reducing the risk of collisions.
  • Acopian Bird Savers. These closely spaced ropes, sometimes referred to as “zen curtains,” hang over windows. They function similarly to tape or decals, but they are simpler to apply and sometimes have a nicer appearance. We use them to protect the windows at the Cornell Lab headquarters because they are very effective. You can create your own or order them to fit your windows.
  • Screens. If you install mosquito screens on the exterior of your windows and cover the entire surface, the results will be very effective.
  • Netting. Cover the exterior glass with netting that is at least three inches a