Mortality Threat to Birds - Collisions with Buildings

The Problem

Emory University Math and Science Building. Photo: John Wegner

In the 1970’s it was estimated by a leading scientist of bird collisions with windows, Dr. Daniel Klem, Jr., that between 97.5 and 975 million birds were killed by collisions with windows in the United States every year.

By 2006, Dr. Klem wrote that even the upper end of his estimate may be highly conservative, based on subsequent studies published in the literature that have found high collision rates in a variety of settings, from suburban office parks, to low and high rise commercial buildings in urban settings. Many of the victims are birds whose populations are in decline. These collisions represent a significant, increasing, and largely invisible problem that has only recently come to be more widely acknowledged by conservationists and governments. Such collisions represent another of the cumulative impacts on bird populations struggling to survive habitat loss and degradation, pesticide poisoning, predation by cats, and other collision threats.

Collisions with buildings are both a daytime and a nighttime hazard.

At night: the intrusion of light into migratory bird flyways poses added danger to an already perilous journey. The interior and exterior lights on tall buildings and bright uplights used for decorative illumination of monuments, government offices, parking garages , and other structures of all heights, emit light fields that can entrap birds. The birds are reluctant to fly from a well lit area to a dark one, particularly during periods of low cloud cover or inclement weather when views of the stars and moon, which serve as navigational aids, are obstructed. The birds circle repeatedly within the light field, and as more and more birds are drawn into the light, they collide with each other and the building, or fall to the ground from exhaustion. If they are not killed immediately by the collision, they are at risk for death from injuries they have incurred, predation on the ground, and collisions with windows during the following days.

During the day: stopover migrants and those that survive night strikes are at risk from collisions with windows as they seek cover and food to build up their fat reserves and resume migration. Surrounded by windows in urban and suburban buildings, birds are at risk because they are not able to perceive clear or reflective glass as a barrier to be avoided. It is likely that all buildings kill some birds, yet we know that certain configurations of glass are particularly dangerous, including windows that reflect habitat and sky; “see through” corridors where transparent glass provides views through corners, walkways or other surfaces to internal and external greenery; attractants, such as bird feeders placed within 1-15 meters of glass, and buildings located in bird-rich areas and along migratory flyways. The collision threat posed by windows has increased with the number of new buildings, and as more of our modern buildings are wrapped in glass exteriors that use larger panes of highly reflective plate glass . Green building certification programs promote the use of glass to increase natural light (a technique known as “daylighting”) and other design elements that have had the unintended consequence of increasing the danger of these otherwise “green” buildings to birds. Mortality associated with window strikes is profound. Studies have documented that between 50%-90% of birds involved in collisions die, usually from internal hemorrhaging.

The Solutions

Patuxent National Wildlife Refuge Visitors Center. Photo: Holliday Obrecht/USFWS/Bird-Safe Building Guidelines

Light: In practical terms this is the easiest problem to solve by simply turning off unnecessary lights at night. This has the added advantage of reducing energy consumption and greenhouse gas emissions that contribute to global warming. . “Lights Out” programs are most effective when undertaken on a city-wide basis. Cities such as Toronto, Chicago, and New York have involved civic leaders, building owners and managers, and other stakeholders in programs that register and recognize participants, and have saved money, resources, and the lives of many thousands of birds as a result.

Windows: For new construction and renovation of existing buildings, windows can be designed to reduce collisions by incorporating patterns in or on the glass, and muting reflections of habitat and sky to alert birds to their presence. Other design innovations to deter bird collisions include angling glass downwards at an angle of 20 degrees or more to reflect ground instead of sky , using sunshades, sunscreens, and other external devices to shield windows, and situating landscape attractants such as trees and bird feeders within 3 feet of windows. Existing windows at both a residential and commercial scale can be modified or “retrofitted” with netting, exterior films, sandblasting, interior window fittings, and the dense application of decals or other visible elements, to reduce or eliminate collisions.

ABC at Work to Reduce Collisions with Buildings

Light:

• ABC is working to provide information and resources to expand Lights Out programs in cities across the United States with partners that include conservation organizations, federal, state and city agencies, and other stakeholders. We will partner with the U.S. Fish and Wildlife Service’s Urban Conservation Treaty City program, National Wildlife Federation’s Flyway Cities Campaign, and others to support program development and/or expansion.

Windows:

• Canada Warbler killed by collision with window in Chicago. Photo: © 2007 Annette Prince

  While ABC applauds and supports the certification and expansion of “green building” certification programs, the focus of these programs has been on the conservation of energy and other materials and resources without explicitly addressing the enormous mortality windows impose on birds. Quite simply, we do not believe that a building can be defined as “green” if it is killing birds. ABC is thereforeworking in partnership with conservation organizations, architects, private organizations, and government agencies and legislators to promote the concept, in the public and private sectors, of bird safety as integral to the definitions of “high performance green buildings” and "environmental sustainability."
• ABC is working to expand window modification projects in areas of important bird habitat, including National Wildlife Refuges, conservation areas that are part of ABC and other habitat programs, and in backyards across the nation. Such projects will save birds, educate visitors about collision deterrence by demonstrating window retrofits in action, and provide other collision prevention strategies they can apply in their homes and communities.
• ABC works with the Bird-Safe Glass Foundation to encourage development of a new type of glass product that will be visible to birds but appear transparent to people, the future “high tech” solution to bird collisions with windows.
  

What You Can Do

• Make your habitat, however big or small it is, safer for birds. Situate your bird feeder within 3 feet of a window.
• Take a look at your home from a bird’s perspective to see which windows reflect habitat and sky, or present a sight corridor from one side of your home through the other. Make these visible to birds with interior blinds and curtains, or exterior screens, film, or a dense application of decals or tape with not more than 4” separating a vertical pattern.
• Resources for screens and exterior window film include: www.birdscreen.com and www.lfdcollidescape.com
• Office workers and residents of apartment buildings should ask building managers to have the exterior vanity lights and flood lights turned off at night, especially during migration seasons.
• If you live or work on the upper floors of a building, keep your blinds drawn from 10:00pm through dawn.
• Move house plants away from windows so birds do not mistake them for available habitat.
• If you are designing/building a house or commercial building, make it bird-safe. Consult Bird-Safe Building Guidelines, available at www.nycaudubon.org and City of Toronto’s Bird-Friendly Development Guidelines, available at http://www.toronto.ca/lightsout/pdf/development_guidelines.pdf.
• Join a volunteer program that not only works with building managers to reduce light pollution, but rescues injured and disoriented birds.
• If you find a stunned or injured bird, follow instructions on the www.flap.org web site. Click on Being Bird Friendly, and follow the link to instructions, or contact your local wildlife rehabilitation center (see directory at: http://www.southeasternoutdoors.com/wildlife/rehabilitators/directory-us.html)
  

More Information

Fatal Light Awareness Progam, www.flap.org

Audubon Chicago Region, www.lightsout.audubon.org

Birds and Buildings Forum, Chicago, www.birdsandbuildings.org

New York City Audubon, www.nycaudubon.org

Cooper, Brian A. and R. J. Ritchie, (1995) The Altitude of Bird Migration in East-Central Alaska: a radar and visual study. Journal of Field Ornithology, 66 (4): 590-608.

Dunn, Erica H., (1992) Bird Mortality from Striking Residential Windows in Winter. Journal of Field Ornithology, 64 (3) 302-309.

Klem, Daniel Jr. (1989) Bird-Window Collisions. The Wilson Bulletin, 101 (4): 606-620

Klem, Daniel Jr. (1990) Collisions Between Birds and Windows: Mortality and Prevention. Journal of Field Ornithology, 61 (1) 120-128

Klem, Daniel Jr. (2006) Glass: A Deadly Conservation Issue for Birds. Bird Observer, 34 (2) 73-81.

Longcore, Travis and Catherine Rich, eds. (2006) Ecological Consequences of Artificial Night Lighting. Island Press, Washington, D.C.

O’Connell, Timothy, (2001) Avian Window Strike Mortality at a Suburban Office Park. The Raven, 72 (2)

Ogden, Lesley J. Evans, (1996) Collision Course: The Hazards of Lighted Structures and Windows to Migrating Birds, Published by World Wildlife Fund Canada and the Fatal Light Awareness Program