Description
Birds generally do not see clear or reflective glass (Klem and Saenger 2013). Glass reflectivity and transparency create a lethal illusion of clear airspace that birds do not see as a barrier. During the daytime, birds collide with windows because they see reflections of the landscape in the glass (e.g., clouds, sky, vegetation, or the ground);or they see through glass to perceived habitat (including potted plants or vegetation inside buildings) or to the sky on the other side. At night, during spring and fall bird migrations when inclement weather occurs, birds can be attracted to lighted structures resulting in collisions, entrapment, excess energy expenditure, and exhaustion (Manville 2009). This phenomenon has resulted in a number of concentrated avian mortality events. These mass events are less common at city, office or residential buildings, but still a possibility under the right weather and lighting conditions. The majority of collisions with both residential and urban buildings happen during the day, as birds fly around looking for food. Large avian mortalities at night more frequently occur at communication towers, offshore drilling platforms and in other situations where there is a bright light source in a dark area, especially during inclement weather. Annual bird mortality resulting from window collisions in the U.S. is estimated to be between 365-988million birds (Loss et al. 2014). While most people consider bird/glass collisions an urban phenomenon involving tall, mirrored-glass skyscrapers, the reality is that 56% of collision mortality occurs at low-rise (i.e., one to three story) buildings, 44% at urban and rural residences, and <1% at high-rises (Loss et al. 2014).
Source for the above text: Reducing bird collisions with buildings and building glass best practices, US Fish And Wildlife Service Division Of Migratory Bird Management, Falls Church, Virginia, January 2016 (updated July 2016) (https://www.fws.gov/migratorybirds/pdf/management/reducingbirdcollisionswithbuildings.pdf)
Because of this issue, the US Fish and Wildlife Service Division of Migratory Bird Management recommends tall buildings to have bird-friendly windows. The recommendation is to create visible patterns that have a good color contrast with the background on the glass to break up the reflective areas of the glass. You may read more about the specifics of the recommendation following the link above.
- Now, think about the dynamics involved during the collision
- Why the impact between the flying bird and a glass window is deadly for the bird?
- Making realistic assumptions and using the principle of linear impulse and linear momentum, find the significance of the force of impact on the bird
