A national standard for bird-friendly building design

The visual markers on a glass façade must be at least 16 to 25 m (52 to 82 ft) above grade to ensure reflections of nearby trees do not create an attractive illusion to birds.
The visual markers on a glass façade must be at least 16 to 25 m (52 to 82 ft) above grade to ensure reflections of nearby trees do not create an attractive illusion to birds.

A building designed with 25 to 40 per cent glass surface, a relatively low window to wall ratio, reduces lethal bird strikes. It is recommended to reduce see-through effects on buildings, such as glass-lined bridges, corridors (linkways), the walls around atria, outdoor railings, glass panels as noise barriers, and where sheet glass walls meet in corners, or treat these respective clear panes with markers following the 2 x 4 Rule. It is advisable to not design and construct buildings with glass-lined courtyards or open-topped atria unless bird-safe glass is used. Even then, in the case of open-topped atria, netting or another roof barrier must be installed to prohibit bird access.

Ventilation grates below or near windows must have openings no greater than 20 x 20 mm (25/32 x 25/32 in.) or 40 x 10 mm (1 19/32 x 13/32 in.) to prevent injured and dead strike victims from passing into wells they cannot escape or be retrieved from, respectively. Interior plants should not be placed near untreated windows such that they are visible as birds may attempt to fly to them. Bird feeders must be placed not more than 0.5 m (2 ft) from the surface of a window. Birds the size of a sparrow perched just a bit over 1 m (3 ft) from the glass surface can fly into a window and kill itself outright. Attractants such as bird feeders and vegetation placed within 0.5 m of the window surface protect birds by limiting their ability to build up enough momentum to injure or kill themselves.


Exterior lighting should be installed to project downward with no upward leakage, to be dark sky compliant. For commercial buildings, it is recommended to prevent interior lighting from entering the outdoors where it can attract birds to the window hazard after business hours, and from sunset to sunrise in all buildings. During nighttime, wherever possible, it is recommended to use task lighting instead of section building luminaires.

Bird strikes and consequent fatalities at night are rare events, occurring almost exclusively over urban areas in North America, during inclement weather with low cloud cover, forcing nocturnal migrants to fly lower on passage and to be attracted to projecting city lights from high-rise buildings. Both birds and moths are attracted to lights, and the brighter the light, the greater the attraction. The deceptive feature of sheet glass is not an issue under these conditions. However, light-attracted birds swirl in and out of the light. They are as likely to injure or kill themselves hitting one another as the birds are, in this situation, the high-rise buildings. As the birds move around the light they become exhausted, flutter to the ground, and are then in the canyons of concrete and glass where they become vulnerable to clear and reflective windows. Keeping lights from attracting birds to the vicinity of building windows at all levels of elevation will reduce the risk of a fatal strike.

The lethal hazard glass poses for birds will not go away unless the measures described in CSA A460:19 are enacted. Unlike the intractable complexity of solving the problems created by climate change, building professionals can solve the fatal hazard glass poses for birds. This can be an environmental challenge with a happy ending, but it will not be so unless architects, developers, and building owners collaborate with those interested in protecting birds, and act to make designs and actual structures safe for birds.

Daniel Klem, Jr., PhD, is the Sarkis Acopian Professor of Ornithology and Conservation Biology at Muhlenberg College, Allentown, Pa. An expert in avian mortality that is attributable to windows, Klem evaluates methods to prevent bird collisions and develops new bird-safe panes for remodelling and new construction. His research has resulted in U.S. patents to guide the development of films and windows using ultraviolet (UV) signals that birds see. He can be reached at danielklem@muhlenberg.edu.

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