Busting Bird-safe Building Myths

By Alan Scott and Heidi Trudell

Did you know that 74% of Americans drink coffee every day? The coffee berry borer beetle and other pests are a major threat to the availability of your morning cup, and birds are the most effective means for coffee farmers to control pests. Half of these beetle-munching birds migrate to North America every spring, and unfortunately many don’t return. Why? Habitat destruction and outdoor domestic cats are primary culprits, but unmarked glass on buildings is also a leading cause.

Collisions with windows are conservatively estimated to kill more than one billion birds annually in North America (recent studies suggest actual mortality may be more than 2 times higher). Coffee is of course not the only reason we should be concerned. Birds are inherently valuable living creatures, they reward us with biophilic joy, generate $41 billion annually in economic activity from birdwatching, and provide an array of priceless ecosystem services (such as post-wildfire regeneration).

We can all help preserve these valuable creatures, at home by keeping our cats indoors and marking exterior glass on our residences, and professionally by incorporating bird-safe measures on the buildings that we design, construct and maintain. Many cities, including Chicago, New York, Portland, San Francisco and Toronto, have adopted bird-friendly building guidelines and ordinance, and LEED has a bird-collision deterrence innovation credit. Several glazing manufacturers now offer bird-safe glass to reduce bird strikes. Even with growing awareness of the deadly impact buildings have on birds, numerous misconceptions about this nuanced subject persist, so let’s dispel common myths and review best practices.

First, a reminder of the primary causes of collisions and the problem areas on buildings. Birds do not perceive glass as a solid barrier. Reflective glass mirrors the landscape or sky they are flying through and appears open for continued flight. Transparent glass is invisible, with the trees and sky seen on the other side inviting their forward motion. This is especially true of transparent corners, glass-enclosed skybridges and walkways, and glass guardrails. Mullions or joints between panes of glass are not enough of a marker to alert birds to the hazard.

Traditional solutions to reduce bird strikes include limiting glazing area, shading over windows, keeping landscaping away from glass walls, and turning off building lighting at night (during migrations), but these are minimally effective. Scientific knowledge about the causes of collisions, and advances in technology for bird collision deterrence are fast replacing these old approaches. Best practices now suggest using patterned glass with frits, etching or UV coatings, but not all solutions are equally effective in all locations. Let’s dispel some myths and review preferred solutions.

Bird-window collisions comparison between low-rise, residence, and high-rise buildings.
Photo courtesy Brendon Samuels

Because declines in migratory bird populations are a cause for concern, and because the primary migration routes run north and south, some argue that bird-collision deterrence is only required on north and south elevations of buildings. However, migrating birds will stop over to rest and refuel along their journey in places where they navigate locally in all orientations and may interact with all sides of a building. Further, non-migratory local bird populations are of additional concern, and they fly in all directions year-round.

Similarly, some project teams will try to dismiss the need for bird collision deterrence because the building is not located directly on a designated flyway. This is a misconception because the primary path of migration may vary from year to year, due to jet stream variation, weather and other environmental factors. Even in a normal year, the breadth of the Mississippi Flyway broadly includes everything from Chicago to Cleveland, and beyond.

Bird-safe building ordinances are misconstrued as optimal rather than minimum requirements to make buildings safer. For example, a maximum window-to-wall ratio per building face may be required to avoid marked glass mandates, but if that allowable area in concentrated in large expanses of glass, the building will still be very hazardous to birds. So as not to limit design options, jurisdictions avoid overly prescriptive ordinance, but this flexibility means that architects must seek to understand the intent of the applicable standard and apply their creativity to blend optimal collision deterrence with the overall design.

Bird-safe glass is increasingly available, but it is not a magic solution. For instance, even tested materials that achieve a low threat factor score may be less effective or inappropriate in certain applications. For example, UV-reflective coatings, which can increase visibility for many bird species while remaining nearly imperceptible to humans, don’t work well on windows facing north, or under overhangs, or overcast skies that block direct sunlight from contacting the glass. Similarly, markings are often added to the number 3 surface of insulated glazing units (outer surface of inner lite) where the low-E coating on the number 2 surface creates enough reflection that the markings are obscured. Patterned glass is most effective if markings are added to the number 1 (exterior) surface. Additionally, current guidelines indicate that 2×2 spacing of markings (not more than 2 inches apart vertically or horizontally) is needed to prevent most collisions.

In place of bird-safe glass, exterior screens and grills can deter bird-collisions and provide heat gain and glare reduction for buildings, and metal guardrails are a bird-friendly alternative to glass rails on balconies. Bird collision authority, Dr. Daniel Klem Jr. in his book “Solid Air,” said, “To be effective, the solution must physically keep birds from glass or visually transform the space windows occupy into a barrier that birds will see and avoid.”

We must make our existing and new buildings safer for our avian friends, for their own sake, for the health of ecosystems, and for human well-being, whether you drink coffee or not. Architects should educate themselves on the science, seek the advice of experts, and apply their creativity to create beautiful buildings that are also visible to birds.

Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect and consultant with over 35 years of experience in sustainable building design. He is director of sustainability with Intertek Building Science Solutions in Portland, Ore.

Heidi Trudell is a biologist turned architectural consultant who has been working on bird collision prevention since 2003. To learn more, follow Scott on LinkedIn at and Trudell at