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

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

What causes a bird to begin the migratory process?

Beneath all those feathers, avian morphology and neurology are incredibly complex. Shared in this complexity is the behavior of migration, which many birds undergo for a variety of reasons. The mechanisms that trigger migration are not completely understood and vary between species, however, there exist certain changes that contribute to birds undergoing the process. In tandem with seasonality, changes in photoperiod and temperature can provide the impetus for a bird to begin migrating. Differences in day length and average temperature also impact the availability of food, which can also cause birds to migrate. Even on the individual level, specific genetic differences can be the motivating force for this movement as well. 

All About Birds. (2021, August 1st) The Basics of Bird Migration: How, Why, and Where. Retrieved from https://www.allaboutbirds.org/news/the-basics-how-why-and-where-of-bird-migration/

How do birds navigate during migration?

Despite their typically small stature, birds have incredibly large brains for their body size. Within this tiny but powerful brain, birds are able to use a variety of tools to navigate during the migration process. However, two specific types of navigation strategies are associated with window strike mortality.

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 due to more trees and shrubs near buildings when compared to very urban areas, can reflect the greenery nearby Also, days with heavy fog in the morning also cause high strike rates (as seen in 2021 with nearly 30 birds striking on our campus in a morning). 

On campus: both of these reasons are the driving factors of bird collision. In our generation, the appeal of modern architecture is that buildings have large windows. This can be seen at the newly constructed Campus Instructional Facility and Siebel Center for Design, with large window facades at 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 students studying or security reasons, which causes many birds to strike. When compared to more urban areas like downtown Chicago with large skyscrapers, our campus also has a daytime strike problem with so many large window facades next to trees or shrubs. 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 perpendicular to a large line of trees, where 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, MANY birds strike here. These lights are off at night, so almost all of the birds strike here during daylight hours, enforcing that the proximity to trees is the primary reason why birds strike here. There are also some other areas on campus such as the near walkway at the Civil Hydrosystems Laboratory and 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/