Bird Conservation: Preventing Window Strikes

Our avian friends face many obstacles in the urban landscape including habitat destruction, domestic cats, and windows. Each of these forces kill upwards of a million birds annually, but most people would not think of windows as terrible bird-killing machines. In fact, windows have an estimated annual avian death toll of 31,159,228 in the United States alone.[1] Birds behave as if windows are invisible and will fly into them at substantial speeds, fatalities usually resulting from cranial hemorrhaging.  Windows pose a threat to all birds, but the majority of the birds killed are migratory. These migratory birds play a major ecological role in different parts of the world as pollinators, seed dispersers, and links in the food chain. In order to protect different ecosystems, birds must be conserved and that means treating windows as the serious threat they are. Conservation programs, laws, and bird-friendly window designs are all parts of the solution to mitigate window strikes.

Birds are protected under various legislations such as the Migratory Bird Treaty Act (MBTA) and the Endangered Species Act (ESA) both of which have the potential to be helpful in deterring window strikes. When a bird protected under the MBTA or the ESA hits a window and dies, the owner of the building is responsible for that death and can be brought up on charges. Under the MBTA the owner may face up to $2,000 fines or two years jail time or both and under the ESA face a $1,000 minimum fine.[2] The ESA is restricted to only being able to prosecute window strikes that have killed endangered birds, but it gives rewards of up to $2,500 to individuals who give information that lead to convictions, encouraging nosy neighbors.[3] These legal penalties provide strong incentives for developers, business owners, and homeowners to invest in technology designed to deter window strikes or construct buildings with birds in mind. However, despite the presence of these laws, politics remains a messy business and these acts are not as effective as they may seem.

The MBTA was created in 1918 to prevent population declines of birds used in the millinery trade, and, after 1940, is enforced by the U.S. Fish and Wildlife Service. The language of this act is vague and has for the most part remained unchanged for 100 years. The act states it is “unlawful at any time, by any means or in any manner, to…kill…any migratory bird.” Though the drafters of this legislation were specifically aiming to soften the blow hunting and trapping had on bird populations, they could not have predicted the threats birds would face 100 years in the future such as habitat destruction, domestic cats, and window strikes. Due to the extremely vague language, a window strike or even accidental road kill can be prosecuted under the MBTA. In 1999, however, a court ruled “[b]ecause the death of a protected bird is generally not a probable consequence of driving an automobile, piloting an airplane, maintaining an office building, or living in a residential dwelling with a picture window, such activities would not normally result in liability”.[4] This case set the precedent for how window strikes would be prosecuted under the MBTA until the act is reformed to account for current conservation problems – that is not at all.

bird strike
Imprint of a window strike. Photo taken by pinlux

For bird watchers, animal lovers, and conservationists the main incentive is not saving money in legal fines but rather the value of birds as a natural heritage or a moral obligation to protect species facing human threats. Fatal Light Awareness Program (FLAP), a Canadian bird conservation organization, aims to spread awareness of all the obstacles facing migratory birds and even has a window strike death counter that estimates how many birds have died since the time you open their website. FLAP explains migratory birds rely upon constellations and natural light sources as ways to orient their migration route and how our artificial light sources cause migrating birds at night to alter their migration route and fly into structures such as lighthouses and windows. FLAP has public outreach programs like Lights Out Toronto!, a collaborative initiative between FLAP and the city of Toronto to get privately owned and public buildings to turn off their lights at night for energy and bird conservation. In 2013 under the Canadian Species at Risk Act it became illegal to kill or injure wild birds with reflective windows on buildings, resulting in businesses investing hundreds of thousands of dollars in bird-friendly window technology.[5] The Lights Out campaign is so popular that cities in the United States are also adopting it. Lights Out DC! is run by City Wildlife, an organization dedicated to protecting the wild animals of D.C. Volunteers collect dead and injured birds around the city to encourage building owners to bird-proof their windows, but their ability to take legal action is hindered, meaning the U.S. has to rely upon the social conservation movement.

The best place to observe this social movement is the internet in various blogs and forums. On the Purple Martin blog, individuals discussed the pros and cons of taping strips on your windows to discourage window strikes. Commenter dsonyay said removing the tape after the purple martins left for the winter was a messy process and other members of his family did not appreciate the tape’s lack of aesthetics.[6] The Hummingbird Forum is concerned with feeder placement and window strikes. Commenters unanimously agreed it is best to have the feeder as far away from the window as possible.[7] The Purple Martin and The Hummingbird Forum only discussed the value of their namesakes and ignored the conservation of all other bird species. dsonyay decided he would make his windows strike-proof only during the summer months in order to save the purple martins, forsaking winter migrants.  Despite this single-mindedness, bird lovers/watchers would and do invest in window strike preventative methods. If dsonyay already possessed a window designed to prevent window-strikes, not only would this help all migrants, but  the purple martins would be safe from his windows as well – which is all he seems to care about. These narrow mindsets of “save the purple martins” and “save my company money” do not have a negative effect on [window strike] conservation since both minds would decide to buy a bird-friendly window or window product (if we had legislation that fined window kills). In order to make this conservation happen, bird-friendly window products need to appeal to businesses and homeowners.

Birds sometimes purposely fly at glass to access habitat reflected in the window pane. In a building design and landscape context,  the more windows a building has, the more window strikes will occur and the closer vegetation is to the window, the more strikes will occur.[1] Minimizing the number of windows and placing vegetation away from clear and reflective glass will reduce the number of window strikes a building will have. Landscapers and builders who want to protect birds should take these preventative measures, but bird-friendly window designs are being developed that may negate the need to install less windows and be mindful of landscaping.

parachute-cord-from-outside
Parachute cord window model by Jean Chamberlain

In order for birds to recognize windows as an obstacle they need to avoid there has to be a visible pattern uniformly placed on the pane. There are a few popular products such as window stickers that claim they reduce bird window strikes. The cute bird and leaf shapes appeal to businesses and homeowners who want to feel as if they are contributing to bird conservation. However, these stickers only work if they are placed 5 to 10 cm apart across the entire window. This is not aesthetically appealing and obstructs the view from inside. These stickers are typically purchased individually and are not sold in such a way that promotes or encourages the average consumer to make the bulk sales needed to cover just one window. A few window models incorporating bird-friendly patterns into their design exist such as the ceramic frit and parachute cord models. The ceramic frit model places circles of ceramic frit between two panes of glass in a polka-dot pattern with each circle being 0.32 cm apart from the next. This model has proven effective at deterring bird strikes for the most part, but problems arise at certain times of the day when the outer pane reflects surrounding vegetation and the circles are obscured.[8] The parachute cord model uses parachute cords vertically placed 10 cm apart over the outside pane. This model has proven to be the most effective bird-friendly window, reducing window strikes by 90% compared to traditional clear glass when cords are placed 8.9 cm apart.[9] Though these models are ready-made and each piece of the pattern does not need to be bought separately, most businesses and home-builders/buyers do not want their view of the outside world obstructed by these patterns. There needs to be another option that will look like traditional glass windows and still deter window strikes.  

Birds see a wider color spectrum compared to humans, meaning birds can see ultra-violet (UV) frequencies while those wavelengths remain invisible to humans. Window models with UV patterns are more widely accepted as the better alternatives to glass windows, since they do not obstruct views. A few UV models and products exist including the ORNILUX Mikado model, UV- absorbing plastic strips, and the complete UV-absorbing film covering. The strips and film covering are applied to traditional glass and reflective windows to transform them into bird-friendly UV windows. The film covering prevents 66% of window strikes compared to clear glass while the strips prevents 77%.[9] Despite the UV-absorbing strips superiority to the complete film covering, the covering may be preferred by consumers due to aesthetics as the strips visibly texture the window. In contrast, the ORNILUX Mikado model proved to be more lethal than clear or reflective panes, killing 17% more birds than the clear glass control.[8] Researchers speculated this is due to the quality of UV reflectance. Previous field experiments revealed 20 – 40% of UV reflectance over 300 – 400 nm successfully prevented window strikes. The ORNILUX Mikado model only reflects 7 – 22% in the 300 – 400 nm range. Surely, other window models with UV reflectance over the 300 – 400 nm range exist and are available on the market, however these UV models are still very expensive compared to traditional windows and, unless the legal fines for killing migratory and endangered birds are enforced, businesses and homeowners will not see a monetary incentive to bird-proof their windows.

In conclusion, the United States still has a long way to go in terms of policy reform and marketable bird-friendly window models in order to circumvent the avian death toll caused by windows. In a perfect world, we’d all have parachute cords arranged over the outside window pane, not care about aesthetics, and make amendments to the MBTA to make the act compatible with current conservation concerns. Looking into the future, we may see more UV window models and perhaps some legislation saying window strikes could result in a punishable fine. Until then, conservation programs and dysonyay will continue to reach out to the public and protect the purple martins.


[1] Klem, D., Farmer, C. J., Delacretaz, N., Gelb, Y., & Saenger, P. G. (2009). Architectural and Landscape Risk Factors Associated with Bird–glass Collisions in an Urban Environment. The Wilson Journal of Ornithology, 121(1), 126-134. doi:10.1676/08-068.1  

[2] MIGRATORY BIRD TREATY ACT: Summary from Federal Wildlife Laws Handbook. (n.d.). Retrieved April 29, 2016, from https://www.fws.gov/alaska/ambcc/ambcc/treaty_act.htm

[3] The Endangered Species Act Endangered Species Handbook. (n.d.). Retrieved April 29, 2016, from http://www.endangeredspecieshandbook.org/legislation_endangered.php

[4] Rozan, K. (2014). Detailed Discussion on the Migratory Bird Treaty Act. Animal Legal & Historical Center, Michigan State University College of Law.

[5] Birds Protected: It’s the Law! (n.d.). Retrieved April 29, 2016, from http://www.flap.org/law.php

[6] New solution for bird window strikes – Purple Martin Forum. (n.d.). Retrieved April 29, 2016, from https://www.purplemartin.org/forum/viewtopic.php?t=21796

[7] Window Feeders and Window Strikes. (n.d.). Retrieved April 29, 2016, from http://www.network54.com/Forum/439743/thread/1435610388/last-1435761930/Window Feeders and Window Strikes

[8] Jr, D. K. (2009). Preventing Bird–Window Collisions. The Wilson Journal of Ornithology, 121(2), 314-321. doi:10.1676/08-118.1

[9] Klem, D., & Saenger, P. G. (2013). Evaluating the Effectiveness of Select Visual Signals to Prevent Bird-window Collisions. The Wilson Journal of Ornithology, 125(2), 406-411. doi:10.1676/12-106.1


Thank you for reading. This is actually my final paper for my Urban Ecology class. Please follow my twitter for updates on my works.

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