The opening of the new Minnesota Vikings’ U.S. Bank Stadium last year was a source of pride for the community and fans. The reputation was soon marred, however, when it was revealed that the large expanses of glass and prominent location on the Mississippi Flyway (a major corridor for migratory birds) made it a death trap for birds.
Far from an isolated incident, multiple studies reveal that buildings are the second leading anthropogenic cause of bird mortality in the U.S., killing almost 1 billion birds annually. The impact from buildings is magnified, as natural causes of bird mortality from predation take the weakest in the population, while glass collisions often kill the fittest. This is a big concern as 25 percent of North American bird species are on the U.S. Watchlist of Birds of Conservation Concern and need our protection. Birds provide important ecosystem services in pollinating plants, disbursing seeds, and providing natural insect and rodent control.
The primary building hazard for birds is glass. Birds do not perceive glass the same as humans. We use visual cues, context and experience to identify large areas of glass we might otherwise walk through, but birds do not have the same ability. The location, configuration and character of glass, along with light conditions, can alter what a bird sees when it encounters a glazed building. Reflective glass (or even clear glass under certain sky conditions) acts as a mirror, creating a deceptive continuation of the sky or adjacent landscapes. Transparent glass is a deadly, invisible barrier for birds flying toward destinations seen on the other side. Corner windows, glass-enclosed sky bridges and glass guardrails pose some of the greatest hazards, with the most troublesome windows being in the first 40 feet above the ground, and those adjacent to vegetated roofs and landscaped courtyards.
Light pollution is another factor that can exacerbate window collision hazards for birds. Birds most at risk from building collisions are not non-native urban invasive species like pigeons and starlings, but migratory species. Birds migrate at night, using celestial cues to help them navigate. They are also photophilic, meaning they have a strong attraction to light. Excessive light pollution, especially during the spring and fall migration, can draw birds in to developed areas and expose them to greater risk of window strikes and urban predators. This is particularly true of unshielded lights and blue-rich white light sources (>3,000 Kelvin).
To address this problem, many cities including New York, Chicago, Toronto, San Francisco and
Portland, Ore., as well as the state of Minnesota, have all adopted bird-friendly building design guidelines to educate building owners, architects and homeowners about the issue and possible solutions. The U.S. Green Building Council even adopted a Bird Collision Deterrence pilot credit that creates quantifiable standards for bird-friendly buildings.
Some of the most effective solutions focus on selecting glazing that is visible to birds, especially in the high hazard locations noted above. Potential products include fritted glass, acid-etched glass and silk-screen patterns.
The new Oregon Zoo Education Center in Portland used a decorative acid-etched pattern on the outside of the glass to prevent window strikes. One of the most innovative solutions is a UV-reflective coating to create a pattern on the glass that is visible to birds but not humans, allowing safer glass without changing the appearance to humans.
A number of high-quality, exterior-applied window films have been developed that improve bird safety and provide the added benefit of reducing heat gain and glare. A wide variety of attractive patterns can be used to make glass visible to birds, including horizontal or vertical lines, dots, and freeform graphics, as long as they follow the “2 by 4 rule” (birds typically will not fly through spaces less than 2 inches high, or more than 4 inches wide). The American Bird Conservancy developed the Bird-Smart Glass Program field-testing methods to quantify the effectiveness of different products at bird-collision deterrence (score of 0-100, greater than 70 is considered bird-safe).
The Jacob K. Javits Convention Center in Manhattan was one of the worst bird killers in the city, but a recent retrofit designed by FXFOWLE, New York City, replaced the existing reflective glazing with low-reflectance glass with a fritted dot pattern. This reduced bird collisions by over 90 percent while also improving thermal performance, daylight and visual transparency.
Architects have also developed creative solutions outside the glazing, such as the ceramic rod screens on the New York Times Building and the exterior metal trellis on the Edith Green-Wendell Wyatt Federal Building in Portland. Awnings and overhangs over glass walls can also reduce
(but not eliminate) bird hazards.
Other solutions involve landscaping and lighting. Avoiding tall trees and shrubs directly adjacent to window walls reduces the attraction of birds to hazard areas. Minimize exterior lighting and specify fully shielded exterior lighting with a warmer color temperature (less than 3,000 Kelvin), compliant with International Dark Sky Association’s Fixture Seal of Approval, and program interior lighting and unnecessary exterior lights to be off during unoccupied building hours. Building owners and homeowners can participate in the National Audubon Society’s Lights Out program, turning off lights at night during the critical migration months. Additional resources on deterring bird-collisions can be found at the Cornell Lab of Ornithology and Audubon.
Innovative approaches to bird-friendly building aren’t just for the birds. To borrow a concept articulated by Ilana Judah, principal and director of sustainability at FXFOWLE, improvements in glazing technology have led to an increased use of glass in modern building, giving architects the ability to create beautiful, transparent and expressive structures, but not without costs. She points out that buildings with floor-to-ceiling, wall-to-wall glass generally use more energy, have greater issues with thermal and visual comfort and create privacy issues (especially in residential), as well as inviting significantly more bird collisions. Perhaps a different approach to design, one that uses occupant comfort, energy performance and other environmental considerations such as bird-friendly design as drivers of architectural expression, could create the beautiful buildings of the future while protecting our feathered-friends and the environment we all depend upon.
* Jacob K. Javits Convention Center in Manhattan; Images courtesy of FXFOWLE; Photography by Chris Cooper
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Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with nearly 30 years of experience in sustainable building design. He is a director with YR&G Sustainability in Portland, Ore. To learn more, visit www.yrgxyz.com and follow Scott on Twitter @alanscott_faia.