Building Bird Collision

Each year hundreds of millions of birds die in collisions with man-made structures that are mostly windows and buildings, communication towers, and wind turbines. The rates of mortality of birds that collide with different types of man-made structures are different. To get an idea of these rates in the United States alone, consider the following estimates:

Based on these estimations, we can see that up to one billion birds are killed every year in the United States by flying into plate glass windows. This by far is the first reason behind birds’ death. Unlike some sources of bird mortality that predominantly kill weaker individuals, there is no distinction among victims of glass. Because glass is equally dangerous for strong, healthy, breeding adults, it can have a particularly serious impact on populations.

Much of this mortality takes place during spring and fall when songbirds are migrating. While songbirds are most at risk from collisions with glass, nearly 300 species have been reported as collision victims, including hummingbirds, woodpeckers, kingfishers, woodcock and birds of prey. We do not usually see dead stricken birds by the buildings. It is most probable that they die elsewhere as a result of the collision. The injured may also be eaten by a cat, raccoon, fox, or dog before we found them.

In fact, birds cannot perceive transparent or reflective glass as a barrier to be avoided. During the day there are two possible scenarios. First, they don’t detect the reflected scene by windows. The hazard to birds is even greater when there is more natural habitat around thus the scene seems more real, and when there are large panes of glass.

Second, when there is a transparent glass that allows views of habitat on the other side of a building or views of plants inside the building: 

Birds can't see glass and don't understand the architectural cues, such as window frames, mullions, and handles, that help people detect it

Even small windows can be dangerous to birds that are accustomed to flying through small gaps between trees and shrubs:

During the night, there is another reason for bird collisions. Lighting is an attractant especially for migrating birds who often fly at night. Brightly lit buildings can draw birds in where they can hit windows or other obstacles. It is said that in cities the biggest kills typically occur at night during spring and fall migrations, when building lights appeared to lure birds into deadly collisions.

In this picture each little spot is a migrated bird that has been trapped in the light beam. They circulated in the beam for several hours until some people reported to turn off the light. 

In order to mitigate the rate of building bird collision, it is recommended to incorporate bird-safe design elements into new architecture for commercial buildings and homes at early stage. In case of existing buildings, retrofitting is another solution: For example, applying tape, film, paint, or decals to the exterior to create visual barriers; installing netting in front of the glass or using exterior shutters; and modifying interior and exterior lighting regimes.

In broader view to this problem we can notice that, while all native birds are protected by law, such sources of mortality (i.e. window collisions) are simply overlooked. Now a few communities have some requirements in this case. For instance, the City of Toronto has new requirements for bird-safe design. Minnesota has a state law requiring all state-owned and leased buildings to adhere to “Lights Out” parameters to benefit migrating birds and save energy. And Federal legislation has been proposed requiring bird-safe design for federal buildings. (To get the Minnesota Bird-Safe Building Guidelines click here)  

In case of green buildings, LEED has applied some criteria to mitigate this problem (Green buildings by having ample openings, windows and attractive environment for birds, have a potential risk of collision). Provisions related to bird safety are included in the newest version of LEED v3 (2009) as a part of the Innovation and Design (ID) category. Also in some design categories, LEED points may fulfill bird-safety needs at the same time as they fill needs for sustainability and efficiency in other categories. Currently, LEED v4 offers a pilot “bird credit” for those who design and build in a bird-friendly manner.