30,000 Dead Birds and Counting

Townsend’s Warbler found during a Seattle Bird Collision Monitoring Project survey.

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Early Estimate of Spring and Fall Bird-window Collision Mortality from the Seattle Bird Collision Monitoring Project

You may have heard the heart-breaking statistic that more than one billion birds die each year in the United States after colliding with glass. Seattle’s birds are among the victims of this environmental catastrophe. In 2020, Birds Connect Seattle launched Bird-Safe Seattle and the Seattle Bird Collision Monitoring Project to improve our understanding of the the issue and and inspire action to prevent collisions.

Since the fall of 2021, nearly 200 Birds Connect Seattle volunteers have spent more than 900 hours monitoring commercial, institutional, and residential structures for evidence of bird-window collisions. Sometimes the evidence is as obvious as a dead bird laying under right under a window. But often the signs are more subtle: a smear of blood on a window or a feather pile in the bushes (scavengers often find carcasses before we do).

Thanks to careful searching of Birds Connect Seattle volunteers, the toll collisions have on our local birds is becoming clear.

Our analyses suggest that collisions with windows kill nearly 30,000 birds at residential and institutional buildings during peak spring and fall migration periods. The models estimate that 19,000 of these are immediate fatalities, with an additional 9,000 deaths possible from collision-related injuries that are not immediately fatal. Please note that our dataset is still maturing. The models and our confidence in the estimate will improve as we continue collecting data.

table presenting bird-window collision statistics for the City of Seattle

That said, we expect the actual annual death toll to be much higher. This analysis only estimated mortality at institutional and residential structures during a small portion of the year. We know that collisions occur at all types of buildings, from skyscrapers to offices to detached homes, condominium complexes, hospitals, greenhouses, and more. But since our survey data is mostly limited to residential structures and buildings on educational campuses, we conservatively assumed that only these structure types experience collisions. We also restricted our analysis to just peak migration seasons. We know that collisions occur year-round, but surveys completed in summer and winter still represent a small fraction of our dataset, so we have did not include them in the analysis. We expect, too, that the estimate for fall mortality at residential structures will increase and the estimate for spring will decrease as we collect more surveys.

Dark-eyed Junco after colliding with a window | Seattle Bird Collision Monitoring Project

What species do we find most commonly?

Nearly half of the collision evidence we encounter we cannot confidently attribute to any particular species (e.g., dust print, blood smear, non-descript body feathers). For those we can identify, thrushes are the most common casualty, represting 18% of collisions documented by the Seattle Bird Collision Monitoring Project in Seattle proper. Sparrows and warblers are also fairly common, each representing 10% of documented collisions.

How do collisions in Seattle compare to other cities?

Unfortunately, an answer here isn’t readily available. Only New York City has an annual mortality estimate, reporting between 90,000-230,000 migratory birds are killed each year by collisions with buildings. That situates our estimate fairly reasonably, as NYC is a much larger city than Seattle by area and with higher structural and migration densities.

What does this mean?

Thanks to our Seattle Bird Collision Monitoring volunteers, bird-window collisions are now a well documented phenomenon in Seattle with a quantifiable impact on our local birds. The scale of the impact—nearly 30,000 mortalities just during migration periods—demands action. We all have a role to play in reducing collision risk to birds in our neighborhoods. See our tips for preventing collisions here, but importantly, we need to regulate this issue. We will not be a sustainable city until our homes and businesses stop killing wildlife. Please contact your elected officials right now and tell them we need bird-safe building standards, as so many other cities already have.

Take Action Now

We want to join other large urban areas like New York City, Portland, and Vancouver BC by passing bird-safe building policy. You can help us advocate for city-wide solutions to bird-window collisions.

Tell our local lawmakers that we need bird-safe building policy