❮ Projects page Audubon Pennsylvania

The mission of Audubon Pennsylvania is “to conserve and restore natural ecosystems in Pennsylvania, focusing on birds, other wildlife, and their habitats through science, education and advocacy, for the benefit of humanity and the earth’s biological diversity.”

It is estimated that several million to as many as one billion individuals of North America’s native bird species collide with buildings each year with the majority dying on impact. These collisions are caused mainly by the fact that most birds do not understand what glass is: they perceive reflections of trees, the sky and the general landscape on glass surfaces to be real scenes that they can fly into, or they fly into non-reflective glass because it may appear invisible to them. Ambient lighting at night and lights on inside of buildings at night exacerbate these problems. Collisions occur most often during migratory periods when millions of migrating birds pass through cities while traveling between their breeding and wintering grounds. Hundreds of North America’s bird species are affected including many that are uncommon and declining, and collisions are now believed to be one of the most important causes of decline in many of these species. Bird collisions have been monitored in Toronto, New York City, Chicago and other large cities for several decades and it is estimated that one million collisions occur each year in the city of Toronto alone.

It has always been assumed that bird collisions occur randomly and that no species is more likely to fly into a particular structure than another. But data collected suggest that the distribution of specimens may not have been random.

Audubon Pennsylvania wanted to determine whether the distributions were random or not. If non-random distributions were found this would demonstrate for the first time that factors other than glass and lights may also be involved in causing bird collisions. Specifically, they suspected that birds may be interpreting buildings as areas of potential habitat and certain kinds of buildings or groupings of buildings may appear more attractive to some species than to others.