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Collision Control Bird-Friendly Design has Public Art and Energy Efficiency Spinoffs
July, 2007
New development guidelines from the City of Toronto offer a range of solutions for easing migratory birds' flight through urban centres. Most migratory bird species are unable to adapt to living in cities, and during biannual flyovers they become confused and disoriented by a combination of light pollution and the effects of glass in the urban environment.
Although specifically produced as an element of Toronto's green development standard (featured in Canadian Property Management, October 2006), the bird-friendly guidelines outline development and design considerations that could apply in almost any city. Many of North America's migratory bird species are facing significant population decline, and millions of migratory birds are killed in North America each year as a result of collisions with buildings.
There are two means of mitigating the danger glass poses to birds. The first and far more effective approach is to create visual markers. The second and less effective strategy is to mute reflections in glass.
The critical area is 12 metres above grade. Window applications to the first 12 metres are essential for a building to be considered bird-friendly since these dimensions relate to typical city tree heights.
VISUAL MARKERS
Birds begin to perceive buildings as objects to be avoided when the distances between features or patterns on glass is approximately 28 centimetres, with the most effective pattern distances at 10 centimetres or less. Essentially, the denser the pattern, the more effective it becomes in projecting itself as a solid object to birds.
Patterned or fritted glass has an image or abstract pattern embedded in it. By using dots of various sizes and densities, manufacturers can create any kind of image, translucent or opaque. The image in the glass then projects enough visual markers to be perceived by birds. Only non-reflective glass should be used in combination with fritted patterns.
Patterns can also be applied to existing glass with the use of film products. Applied to external surfaces, including windows, film products can be designed with any image or pattern. Film laminates are often applied to downtown buildings for other purposes such as security or advertising, or these products are applied to transit vehicles for advertising purposes. On buildings, the film could be integrated with the architectural design.
A pattern of decals applied externally can also create enough visual markers. However, if decals are used, a pattern with clear spaces of not more than 28 centimetres is required in order for the use of decals to be considered bird-friendly.
Multiple paned glass is an effective visual marker. The vertical and horizontal mullions create an image that is visible to birds, as long as the panes conform to the optimal range of 28 centimetres to 10 centimetres or less, with the smaller distances being more effective.
Exterior decorative grilles are another means of projecting visual markers to birds. Exterior decorative grilles can serve as a bird-friendly development feature as long as they are within the optimal range of 28 cm to 10 cm or less, with smaller distances being more effective.
Artwork installed on the interior or exterior of windows may provide enough visual markers for birds to perceive the glass as a solid object while allowing natural light into the interior space. This could allow developers to provide public art that is also a bird-friendly design so they are urged to think about those two elements in combination.
Birds are able to perceive ultraviolet (UVA-A) light. Currently, there are glass products under development that either reflect or absorb UV wavelengths - ranging from 300 to 400 nanonmetres - that birds can see but humans cannot. This would enable a window to be clear and/or reflective to the human eye, but appear solid to a bird.
Also, photovoltaic panels can be incorporated into windows where photovoltaic vision glass substitutes thin-film, semi-transparent photovoltaic panel for the exterior glass panel in an otherwise traditional double pane glass window or skylight. These panels can be designed to generate enough visual markers for birds to perceive windows as solid objects while also producing renewable energy.
MUTING REFLECTIONS
Angling glass panes in such a way as to project reflected images downward is a fairly effective way of reducing bird strikes, especially at ground level. Angles become effective at a minimum angle of 20 degrees, with 40 degrees known to be more effective.
Installation of internal screens may provide enough visual markers through non-reflective glass for birds to perceive windows as solid objects. To be most effective, they must be installed as close to the glass as possible so as to maximize the visual markers projected through the window.
Awnings and overhangs will cover windows in ground floor lobbies and mute image reflections in them. They can take on a variety of creative forms.
Sunshades are external features designed to reduce direct sunlight into a room while allowing indirect light, thus reducing the demands on cooling systems. They have many variations and can be incorporated into the design of a building in many interesting and creative ways. Sunshades mute the reflections in the glass windows thereby reducing the likelihood of birds flying into them.
Conversely, the location of interior plants, large and small, on the ground floor levels can have a negative impact on birds. Ground floor lobbies and walkways are often decorated with trees and shrubs, and designed with clear glass fenestration. These lobbies are often brightly lit at night, dramatically highlighting any greenery that may be inside.
Brightly lit lobbies with greenery features are extremely dangerous to migratory birds that have been drawn into a city by light pollution and become trapped in the unfamiliar urban environment. Birds, like humans, cannot perceive clear glass and thus will attempt to fly towards the greenery that is perceived as safe habitat. This often results in injury and death as they crash into the window.
To minimize bird collisions, building managers and owners are encouraged to locate any greenery away from clear glass. They are also encouraged to minimize lighting levels though motion-sensitive lighting systems in ground floor lobbies, walkways and corridors, and to retrofit clear glass wherever possible with translucent fritted glass, or to apply window film. These retrofit and application options will produce visual markers to enable birds to perceive the glass as a solid object.
ONSITE HAZARDS
Increasingly, landscape architects and garden designers are specifying mirrors (large and small) in their designs, with the intent to create a reflection and, at times, an infinite repetition of their design. In small gardens mirrors can create an illusion of a larger space. Unfortunately, these surfaces kill and maim birds, as birds cannot distinguish the reflected from real habitat. Mirrors should be avoided in landscape design.
Ventilation grates on a site also present a deadly hazard for birds. An injured and helpless bird that falls onto a ventilation grate with porosity large enough for birds to fall through will find itself trapped when it recovers enough to attempt flight. Ventilation grates should have a porosity of no more than 2 centimetres by 2 centimetres or should be covered with netting in order to prevent birds from falling through. Also, ventilation grates should never be up-lit for this would produce light pollution.
Noise barriers erected at highways and railway rights-of-way to protect adjacent communities from noise present similar problems if portions of noise barriers are constructed with clear polymethyl methacrylate (PMMA) panels. Birds perceive these transparent panels as non-existent and fly into them. These panels present the same dangers to birds as do glass panels on buildings.
Use of glass or methacrylate panels in noise barriers should be avoided. When transparent barriers are present, they should be treated in a way so as to create enough visual markers for birds to perceive them.
The preceding is an excerpt from the City of Toronto's new guidelines, Design-based Development Strategies for Bird-Friendly Buildings. For more information, see the web site at www.toronto.ca/lightsout.
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