Large glass surfaces shape modern architecture – transparent, open, filled with light. For birds, however, they represent an almost invisible obstacle. Every year, countless animals collide with windows or façades because they cannot perceive the reflective or transparent surface. Many property owners and planners therefore resort to stickers or bird-of-prey silhouettes. Well-intentioned as they are, they offer little real protection in practice.
Birds perceive glass surfaces differently than humans. Transparent panes provide an unobstructed view of vegetation or sky; reflective surfaces mirror the surroundings so realistically that they are mistaken for a continuation of the flight path. Particularly dangerous are opposite windows, conservatories, and glass façades with high reflectivity. Birds fly at full speed – often with fatal consequences.
The risk of a collision caused by transparency increases with corner glazing or when an additional window at the back suggests a possible passage. It also rises when lights are switched on behind glass in the evening. Moreover, nighttime illumination of large buildings can itself become a hazard for birds.
The risk of a collision caused by reflection generally increases with higher external reflectance and when reflections show attractive targets for birds.
