Authored by Jo-Annie Gagnon, B.Sc. Education Program Coordinator of Le Nichoir Wild Bird Rehabilitation Centre

Last year, Walker Glass began a series of articles on residential bird collisions. We are back with an article from the perspective of wild bird rehabilitation centre Le Nichoir, located in the Greater Montreal Area. In this article, Jo-Annie Gagnon, B.Sc. shares data and insights from her experience as Education Program Coordinator at Le Nichoir.

Bird collisions with house windows

Caring for wild bird species since 1996, wildlife biologists at Le Nichoir Wild Bird Rehabilitation Centre often triage birds that are listless and have difficulty keeping their balance, occasionally presenting with a swollen head. These are the signs of a bird that has been injured by colliding with a window. Records show that these collisions, in addition to cat attacks, are the two most common causes of injuries and mortality for wild birds admitted to this rehabilitation centre.

Bird collision with high-rise building glass is a well documented problem. Increased awareness of this wildlife threat has led to impactful changes, such as bird-friendly building legislation in multiple North American cities. However, avian injuries and death following window collision are not limited to high rises in dense urban areas. Although conservationist groups record urban bird strikes all year round, the numbers for urban and high-rise bird strikes peak during migration seasons. In fact, residential windows are responsible for the largest number of casualties. These findings are reflected in Le Nichoir’s bird admissions data, as most birds admitted for rehabilitation following a window collision are found near houses. This indicates a need for action at residential and individual levels, as well as industrial and commercial levels. Education and pre-emptive steps could have far reaching potential to minimize this leading cause of bird mortality.

Birds, glass and feeders

Window collisions occur because birds have no concept of glass. Reflections of vegetation and sky in window glass are often confused for habitat. Birds may also collide with glass if they are able to ‘see through’ the building. For example, if two windows face each other across a narrow area of the building, birds may try to fly through the apparent empty space. Increasingly popular glass railings pose another serious threat.

At night, indoor lights can confuse and attract birds. This often leads to collisions, especially during the fall and spring migrations.

Feeders can increase the risk of birds colliding with windows. This likely due to the greater abundance of birds around areas with feeders, increasing the probability of a collision. However, despite their possible negative impact, feeders also offer benefits to birds. The threat they pose can be greatly reduced with proper placement. Most bird casualties following a collision have been found to occur when birds flew from a distance over 1m from a window. On shorter distances, the birds do not usually gain the speed needed to cause a serious injury. Placing feeders less than 1m away from windows is a simple way to reduce the risk of severe collisions. Window feeders are a good option, as birds have to slow down before landing on the feeder.

Learn more about the science of bird collisions here.

In rehabilitation

In 1996, Le Nichoir received 420 birds. Now, 25 years later, the centre admits and rehabilitates over 2,500 birds annually. The causes of admissions are varied. They include orphaned birds, car collisions, entanglements, malnutrition and cat attacks. Window collisions represent the second most common cause of injury after cat attacks. It is important to note that this statistic does not represent the number of bird deaths due to collisions with glass. Rather, it accounts for birds who have survived a collision and been delivered to Le Nichoir for rehabilitation.

Bird strikes in general go under-reported. This is because collision victims may be picked up by scavengers, cats, or garbage removal services, or flee the site under their own power if they are able. Even at the rehabilitation centre, many birds admitted show injuries commonly associated with a collision but are only treated as suspected victims of a window strike, and thus not considered in the data. Considering these factors, the death and injury toll from residential glass must be estimated to be far greater than the number of birds actually reported.

As can be expected, migratory birds are admitted at higher-than-average numbers following a window collision. Twenty to thirty percent of all thrushes, warblers, hummingbirds and kinglets received at the centre are victims of a collision with a building. More surprisingly, non-migratory woodpeckers are also common casualties of window collisions. Up to a third of all Hairy Woodpeckers and a fifth of all Downy Woodpeckers admitted to the centre have suffered window collisions. This may be due to their brains’ adaptations to pecking, which can protect them from dying on impact or initial trauma and allow more birds to survive until they reach the rehabilitation centre. Injuries are similar across species. They include beak fractures, head swelling, eye damage, spinal or brain trauma, and wing injuries. In most cases birds require medication, oxygen therapy, and rest time.

Of all birds admitted to Le Nichoir following a window collision, only 40% will survive their injuries.

wild bird rehabilitation centre

Image credit: Wendy Dollinger, President at Le Nichoir

People finding birds after they collided with their house often report that one or two windows are repeatedly the cause of collisions. This suggests that some windows are more prone to confuse birds than others. This may be due to the position of the glass, surrounding habitat, and vegetation. Glassed-in porches are also a commonly cited culprit. The recent trend toward glass guardrails in residential architecture exacerbates the problem.

Unfortunately, some people are reticent to use effective patterned stickers because they ‘’cover the window’’ and often choose to install a few sparse decals which have limited efficacy. Normalizing the use of patterns on glass and increasing collision-deterrent options available to the public, such as window films and bird friendly glazing, will go a long way towards reducing the impact residential windows on bird populations.

Lessons for the industry

This article presents a view from a single wild bird rehabilitation centre. Now, just for one second, imagine what the numbers would look like if you combined all the bird rehab centres in North America. This is a serious issue, one already recognized in bird friendly building legislations across Canada and the United States. Legislations focus on commercial buildings for now, but that will soon change. It is only a matter of time before bird friendly legislation arrives for the residential market, and smart building professionals should look ahead to bird safe homes.

About Le Nichoir

Situated at the entrance to the Clarke Sydenham Nature Reserve in Hudson, Quebec, Le Nichoir’s mission is to conserve wild birds as part of our natural heritage for future generations. Le Nichoir delivers its mission by providing professional and compassionate care to injured and orphaned wild birds, and the development and delivery of public environmental education programs. Le Nichoir admits over 2,500 birds annually, representing over 100 species from more than 180 municipalities in Quebec, making it one of the largest centres of its kind for songbirds in Canada. The Centre offers public education through interactive environmental education programs for children, seminars, family activities, guided or self-guided tours of the Centre, informational kiosks at community events and responding to over 14,000 phone calls and emails annually.

Learn more at


Hager SB et al. 2017. Continent-wide analysis of how urbanization affects bird-window collision mortality on North America. Biol Conserv. 212(2017): 209-215.

Klem D Jr. 1990. Collision between birds and windows: mortality and prevention. J Field Ornithol. 64(1): 120-128

Klem D Jr, Keck DC, Marty KL, Miller Ball AJ, Niciu EE, Platt CT. 2004. Effects of windows angling, feeder placement and scavengers on avian mortality at plate glass. Wilson Bull. 116(1): 69-73

Klem D Jr. 2009. Preventing bird-window collisions. Wilson J Ornithol. 121(2): 314-321

Lao S, Robertson BA, Anderson AW, Blair RB, Eckles JW, Turner RJ, Loss SR. 2019. The influence of artificial light at night and polarized light on bird-building collisions. Biol Conserv. 241 (2020): 108358.

Le Nichoir Wild Bird Conservation Centre. 2021. Bird mortality causes analysis and reach of pilot Wild Bird Helpline in an eastern Canada rehabilitation centre. Report prepared for the ECCC. March 2021.

Loss SR, Will T, Marra PP. 2015. Direct mortality of birds from anthropogenic causes. Annu Rev Ecol Evol Syst. 46: 99-120. Available from: doi: 10.1146/annurev-ecolsys-112414-054133

Machtans CS, Wedeles HRW, Bayne EM. 2013. A first estimate for Canada of the numbers of birds killed by colliding with building windows. Avian Conserv Ecol. 8(2): 6. Available at:

Van Doren BM et al. 2021. Drivers of fatal bird collisions in an urban center. PNAS. 118 (24): 2101666118.

Xufeng N, Yikun N et al. 2014. Bird-building collisions in the United States: Estimates of annual mortality and species vulnerability. Avian Conservation and Ecology. 8(2):2.

Share This