Bird imprint on window | 22kay22 Getty Images, Canva

by Judy Bowes

On September 1, 2021, Seattle Audubon made history by launching the first long-term bird building collision monitoring study in Washington—the Seattle Bird Collision Monitoring project. Outside of a handful of studies from the West Coast, collision research has focused primarily on the Northeast and central areas of North America. By studying building collisions locally, we can gain deeper insights into specific species’ vulnerabilities and how local weather patterns, light pollution, building design, and proximity to vegetation and water contribute to collision risk. The research design intends to inform action by architects, designers, decision-makers, and conservationists to prevent collisions in Seattle, the Puget Sound region, and the Pacific Northwest.

Research to inform future strategy

Bird building collisions are a critical conservation issue negatively affecting bird species across North America. Collisions kill on average 600 million birds each year in the United States, with estimates as high as one billion per year (3). The enormous yearly loss from collisions, along with losses from habitat degradation, pollution, cat predation, and other human-related impacts, has contributed to a 29% reduction in North American bird populations since the 1970s, including a 50% decline in the number of migratory birds (6) . Addressing all impacts to birds is vital to the future of North American birds, and until recently, the impact of building collisions has largely been overlooked. The Seattle Bird Collision Monitoring project will help determine when and why collisions happen in Seattle, adding to the limited body of research on the topic and tailoring collision prevention strategies to local conditions and avian assemblage.

The primary questions driving the Seattle Bird Collision Monitoring project are:

    • How many and what types of birds are victims of collisions in Seattle?
    • What common architectural features in Seattle contribute to or reduce collision risk?
    • What collision prevention solutions are most effective in the real world?

Research to date

To date, the best insight into the number and types of birds impacted by collisions in the Puget Sound region comes from patient intake records at our local wildlife clinic. The PAWS Wildlife Center (PAWS), located in Lynnwood, WA, shared data from 1,100 bird collision patients between 2009-2019. Ten species make up over 50% of the total number of cases. The top three species, the American Robin (Turdus migratorius), Northern Flicker (Colaptes auratus), and Varied Thrush (Ixoreus naevius), account for one in four total cases. Additionally, one in four of these top ten species are from the thrush Family (Turdidae) (4). An important caveat to the PAWS data is that it represents a small and biased sample of the total set of birds impacted by collisions. The PAWS data only includes those collision victims that were detected, survived the collision, and were transported to Lynnwood by compassionate community members. 

bird chart

Even so, the PAWS data agree with a recent study on collisions at eight low- to medium-rise buildings in Vancouver, British Columbia. The study shows that many of the same species reflected in the PAWS data seem to be vulnerable to collisions in the greater Pacific Northwest, such as the Varied ThrushAmerican RobinGolden-crowned Kinglet (Regulus satrapa), Dark-eyed Junco (Junco hyemalis), and Hermit Thrush (Catharus guttatus). Also similar to the PAWS data, the Thrush family is most affected, comprising 38% of total collisions. The Varied Thrush had the greatest number of collisions overall (1).  

Unlike studies from the East Coast or Midwest, the Vancouver study reported a relatively high number of winter fatalities, comparable to fatalities during spring migration. These data suggest that some species are more vulnerable during the winter months. Again, the Varied Thrush tops the list as the species most vulnerable to glass collisions in the winter. Varied Thrush are 76.9 times more likely to collide with glass than species with an average risk of collision. The Spotted Towhee (Pipilo maculatus) is the second most vulnerable species—58.1 times more likely to collide with glass in the winter, but with lower collision risk during fall and spring migration seasons (1). Similar winter collision patterns are likely in the Seattle area as abundant evergreen foliage does not diminish during the winter, which maintains attractive year-round habitat close to structures with reflective glass. Migration patterns and a large number of overwintering birds may contribute to a high number of winter casualties in Seattle, as reported in Vancouver. 

varied thrush

Varied Thrush | BirdImages

spotted towhee

Spotted Towhee | Devon Yu

2Understanding our local species’ vulnerability to collisions, along with their habitat preferences and behaviors such as migration, will help identify and implement design solutions that most effectively prevent collisions. This also depends on understanding local weather conditions and landscape features near the buildings where birds collide with glass.

Conditions for a collision

Despite increasing urbanization and growth, critical patches of habitat remain for Seattle’s resident and migratory bird species. These green spaces provide resources for birds, but the risk of collision increases when located near structures. When located within 50 meters of a building, reflections of vegetation in windows can lure birds closer to dangerous glass surfaces and increase collision risk (3). For Seattle, we are curious to learn how conifers and deciduous trees contribute to collision risk differently, especially in the winter months.

The impact of bodies of water on collision risk is not well known. However, by collecting collision data from buildings both near to and distant from bodies of water, the Seattle Bird Collision Monitoring project may determine if proximity to water affects collision risk similar to proximity to vegetation.

By recording weather patterns and light use at building sites, the Seattle Audubon study can uncover if the Pacific Northwest climate affects collisions during overcast conditions at a different rate than studies from the eastern and the central United States. These studies show that overcast conditions tend to increase building collisions and can lead to large-scale collision events when coupled with light pollution (5). Particularly during migration, the light emitted from buildings through windows or by illuminating the exterior of the building can attract birds to the glass windows and solid surfaces, resulting in higher collision rates (2).

Additionally, flight paths can shift in reaction to these light sources, and the glow from cities can cause disorientation leading nocturnal migrants to redirect their flight path towards the city (5). Moreover, artificial light can be confused for celestial navigational cues sending migrating birds on an energy-draining detour or a fatal flight path towards light-emitting buildings (5).

As the study from Vancouver states, the Pacific Northwest has an expected high rate of fall collisions but a higher rate of winter collisions than studies located in the eastern and central United States (1). Determining if overcast weather is a factor in both the high fall and winter collision numbers would be an important contribution of Seattle Audubon’s study. While assessing the environmental conditions and light pollution at each study building will be a crucial component of the study, determining how design features of Seattle’s buildings contribute to collisions will be central to preventing future collisions in our area.

Dangerous structures

Seattle Audubon’s study focuses on the use of glass and how the environment around the buildings influences the rate of collisions. While the extensive use of reflective or transparent glass by a building or structure typically increases collision risk, moderate use of glass is dangerous too, especially when suitable habitat is within 50 meters of a building (3). Greenspaces provide vital habitat in Seattle, but deadly collisions increase when glass reflects vegetation, is visible through transparent glass, or when green spaces lure birds closer to windows and glass structures. The Seattle Bird Collision Monitoring project will study buildings designed with a large amount of glass and buildings designed with a moderate amount of glass with various amounts of green spaces or bodies of water within 50 meters to inform design strategies to prevent collisions.

moderate glass use building example

Example of moderate glass use, with habitat within 50 meters. Photo by Judy Bowes


Local buildings using a large amount of transparent and reflective glass. Photos by Judy Bowes

How transparent glass and other reflective materials are used in the design is also a crucial aspect of the study. Transparent glass structures, corners, and walkways give birds the illusion of a clear flight path through the building to open sky and green spaces. Further, the study can determine if some design features like external shades prevent collisions by monitoring buildings like the Bullitt Center. Additionally, the study will evaluate if reflective metals are conducive to collisions by monitoring the Museum of Pop Culture. Volunteers participating in the monitoring study will record landscape and design data by marking where collision victims are found relative to landscape and building features.

museum of pop culture

Example of reflective metal at the Museum of Pop Culture. Photo by MoPop.

bullitt center windows

Example of exterior shades at the Bullitt Center. Photo by the Bullitt Center.

Volunteer power

Seattle Audubon’s monitoring study starts with a pilot program during this year’s fall migration. The study is planned to repeat each migration season over at least the next five years. This study depends on community scientists to monitor buildings regularly, and detect collision fatalities, meaning local volunteers drive this project.

In addition to volunteers, building managers and property owners have been essential to securing monitoring sites. The pilot program begins in the Capitol Hill neighborhood with eight building sites. The study has confirmed more sites across multiple neighborhoods in Seattle to be monitored for the entirety of the study beginning with 2022’s spring migration. Seattle Audubon has seen an encouraging amount of enthusiasm from building managers to allow volunteers to monitor their buildings. This early support is promising as solutions to prevent collisions will depend on applying bird-safe design strategies.

Beyond adding to the limited research of bird building collisions in the Pacific Northwest, the study aims to use the gathered data to prevent collisions across Seattle through education and policy. While the data volunteers gather through the Seattle Bird Collision Monitoring project will fill significant gaps in our understanding of bird building collisions locally, we can use the available information to act. In parallel with this project, Seattle Audubon is working to inspire individuals to prevent bird building collisions at their residences and advocating for the city of Seattle to adopt policies that reduce glass and lighting hazards to birds.


Make fall migration safer

Here are four ways you can act now to make Seattle safer for birds during this fall migration, and all year long:

    • Bird-safe your home
      The most important way to help birds is to be proactive by applying bird-safe products to prevent collisions at home and committing to a lights-out program during migration seasons or year-round.
    • Activate your network
      Once homes are bird-safe, the next step is to encourage neighbors and local businesses to adopt a lights-out program and apply bird-safe products to transparent or reflective windows.
    • Contribute collision data
      If you discover a dead or injured bird, report it at These data helps us track the causes of bird mortality and injury across Seattle. If the bird was a collision victim, be sure to treat the window it struck with effective bird-safe products to prevent future collisions.
    • Volunteer
      Sign up to participate in the Seattle Bird Collision Monitoring project! We’re growing the program and will need a large pool of volunteers for future seasons. The next volunteer opportunity will begin in spring 2022.


Bird building collisions are a critical conservation issue threatening up to a billion birds in the United States each year. The Seattle Bird Collision Monitoring project will provide much-needed information to a limited body of knowledge as to why collisions happen, particularly in the Pacific Northwest. Understanding how bird building collisions impact resident and migratory species will inform conservation and building design solutions. This study will lay the foundation for Seattle to act and prevent collisions through a bird-safe city policy. By implementing these actions, we intend to reduce hazards to birds in Seattle’s built environment and help to keep common birds, like the Varied Thrush and Spotted Towhee, common and prevent vulnerable and threatened species from going extinct.


1. De Groot, Krista L, Alison N Porter, Andrea R Norris, Andrew C Huang, and Ruth Joy. “Year-Round Monitoring at a Pacific Coastal CAMPUS Reveals Similar Winter and Spring Collision Mortality and High Vulnerability of the Varied Thrush.” Ornithological Applications 123, no. 3 (2021).

2. Lao, Sirena, Bruce A. Robertson, Abigail W. Anderson, Robert B. Blair, Joanna W. Eckles, Reed J. Turner, and Scott R. Loss. “The Influence of Artificial Light at Night and Polarized Light on Bird-Building Collisions.Biological Conservation 241 (2020): 108358.

3. Loss, Scott R., Tom Will, Sara S. Loss, and Peter P. Marra. “Bird–Building Collisions in the United States: Estimates of Annual Mortality and Species Vulnerability.” The Condor 116, no. 1 (2014): 8–23.

4. Progressive Animal Welfare Society (PAWS). 2020. Patient intake records: known or suspected collision-related injuries, 2009-2019. Unpublished raw data.

5. Rich, Catherine, and Travis Longcore. Ecological Consequences of Artificial Night Lighting. Island Press, 2013.

6. Rosenberg, Kenneth V, Dokter, Adriaan M, Blancher, Peter J, Sauer, John R, Smith, Adam C, Smith, Paul A, Stanton, Jessica C, et al. 2019. “Decline of the North American Avifauna.” Science (New York, N.Y.) 366 (6461): 120–24.

About Judy Bowes

Judy is an architectural researcher and bird building collision consultant. She received her MS in Architecture, History and Theory from the University of Washington where she studied the impacts of the built environment on avian species in the United States. Learn more about Judy by visiting her website,


Other articles in this issue of EarthCare Northwest

bird imprint on window

Wanderlust: Incredible journeys by fascinating birds

Changes in organ placement, personality, or the ability to nap mid-flight are some of the incredible ways birds have adapted to prepare for their bi-annual migratory journeys.

western grebe

Migration: Inspiring authors, photographers, and makeup artists alike

Seattle Audubon Board Member, Grace Rajendran, has a passion for books and birds. She interviewed the authors of Pacific Flyway, a book about waterbird migration, and then used her creativity to create makeup looks inspired by some beautiful migratory birds.