You’ve probably heard the sickening sound of a bird flying into a window, but you may not have heard that annual bird fatalities from such collisions range from 100 million to 1 billion in the U.S. alone. This threat to bird populations is second only to habitat loss, according to ornithologists. Birds can’t see glass, so collisions can happen anywhere birds and glass coexist. Exacerbating the problem, glass often reflects trees and sky—appearing attractive to birds.
There are a number of ways to prevent bird collisions in both new construction and existing buildings, but solutions that can be integrated into the design of a building are most likely to be welcomed by designers and project owners. The new
LEED Pilot Credit 55: Bird Collision Deterrence provides resources for helping buildings integrate solutions, and metrics for measuring success.
Among the more promising solutions is bird-safe glazing manufactured with bold patterns visible only to birds and other wildlife that can see ultraviolet light. A variety of window films that change the reflectivity of existing glazing or create bird-deterring patterns are also available. Etching of glass to reduce reflection can also prevent fatalities, but this technique visibly changes the building façade. All these efforts are most effective when the deterring pattern uniformly covers the entire window, and space between lines is four inches or less in vertical columns and two inches or less in horizontal rows.
Careful design of shading and architectural elements around windows can mitigate bird hazards while also controlling solar gain—benefiting energy efficiency and daylighting. When glazing is angled down at twenty to forty degrees, birds strike at an angle, reducing fatalities. Strategically placed fences and other efforts to block visual contact between flying birds and windows can also be effective.
Bird feeders should be located less than one yard from windows; this way, if birds taking flight from feeders collide with windows, they do so at low speed. Corners of buildings and other areas where it is possible to see through one window and out another are also problematic, as birds may attempt to pass through. Visual barriers between windows, such as blinds, hanging banners, or artwork, can alleviate this problem.
Nighttime poses a special set of risks, as lights can confuse high-flying birds and draw them into urban areas. Minimizing light pollution saves birds and also saves energy. This is especially important during the spring and fall migration seasons.
If you don’t see bird carcasses around a building, that doesn’t mean it’s bird-safe. Scavengers—some of whom have learned which buildings are the most “productive”—may remove dead birds before occupants find them. However, attempting to monitor bird fatalities can help increase general awareness of the problem and alert facility managers to potential weak points in their efforts.