At the macro-level, confusion during migration is the leading cause for bird window strikes.

Nonetheless, where does this confusion come from, and why specifically during migration?

Despite such impressive strategies, artificial light and manmade structures can greatly impact their effectiveness and subsequently lead to mortality.

Window strikes can be blamed as one of the top factors contributing to the mortality of birds. But, why is it so deadly? There are many reasons why a bird may strike a window, but the two main causes are the lights at night and the reflectiveness of windows during the daytime reflecting nearby greenery. Passerines use stars at night when they migrate, so the lights from buildings can easily disorient birds at night, causing them to occasionally fly into windows. On nights with the best conditions for migration (north winds in the fall and south winds in the spring), the strike rate for birds is much higher than on nights with unsupportive conditions for migration. This is likely the top reason why birds collide with windows, although the second reason is also very problematic. Windows, especially in areas of college campuses because there are more trees and shrubs near buildings when compared to very urban areas, can reflect the greenery surrounding them. Also, days with heavy fog in the morning also cause high strike rates as well (as seen in 2021 with nearly 30 birds striking on our campus in a morning). This makes it appear that there are more trees to a bird rather than just a window reflecting it. Due to this, birds also strike windows at high rates in the daytime.

On campus: both of these reasons are the driving factors of bird collision. In our generation, the modern architecture appeal is that buildings have large windows, which can be seen at the newly constructed Campus Instructional Facility and Siebel Center for Design, with large window facades on each building. This is continuing to create more and more problems and our data suggests it's detrimental and costly to birds. Because this is a college campus, most buildings keep lights on at night due to either students studying in these buildings or for security reasons, which causes many birds to strike. When compared to more urban areas like downtown Chicago with large skyscrapers which birds strike primarily at night, our campus also has a daytime strike problem with so many large window facades next to trees or shrubs. For example, the new Siebel Building also has a new tree and shrub planting all along the south side of the building. Due to the proximity to the windows, many birds strike here as well. It is interesting to note that the species of birds we find at this building are migrants that are found in more shrubs and shorter trees, supporting the argument that the plantings right next to the buildings possibly cause this!

Another issue we are currently watching is the "glass walkways" or "glass peninsulas" combined with the surrounding environments around these areas. The prime example is the south side of Beckman which is the most struck location on campus. This is a large glass peninsula extending from the south side of the Beckman Institute which is very problematic to birds, even though the lights are off at night. This feature juts out in-between a large line of trees, of which migrants spend a lot of time foraging for food and flocking together. Because this is an obstacle in the middle of the line of trees, but also reflects the nearby trees making it look like the line of trees continues through the windows, MANY birds strike here. There are also some other areas on campus such as the near walkway at the Civil Hydrosystems Laboratory and the one at the Chemistry Laboratory are also very problematic for the same reasons!

Mass Audubon. (2019, March 19th) Help Us Learn About Bird-Window Strikes Downtown Retrieved from https://blogs.massaudubon.org/distractiondisplays/help-us-learn-about-bird-window-strikes-downtown/