Treatment of glazing
Regarding glazing, a minimum of 90 per cent of sheet glass in a building must be treated where a fly-through or reflective habitats create illusions and risks of a bird strike. The full glazing surface must be treated for non-vision (spandrel glass, shadow boxes, privacy) sheet glass. Birds have fatal collisions attempting to reach their habitat and sky on the other side of clear windows, or when trying to reach the illusion of habitat and sky reflected off of windows covering dark interior spaces. To make sheet glass safe, visual markers are used to transform glazed surfaces into barriers birds can see and avoid. To be effective, the application of visible-to-birds markers must uniformly cover the glass surface, and form contrasting patterns consisting of absorbing and reflecting elements. Among other options yet to be discovered, markers can be created using acid etching, ceramic frit, printing on film, non-film adhesives, and ultraviolet (UV) patterning applied to inorganic sheet glass and organic films. For most applications, organic films are used to retrofit existing structures, and novel bird-safe sheet glass is for remodelling and new construction.
These marker elements can be of any shape, minimally 4 mm (5/32 in.) in diameter or 2 mm (5/64 in.) wide x 9 mm (19/64 in.) long, if linear. They should be separated no more than 50 mm (2 in.), have high contrast with the background, and applied to the outside exterior glass surface. No matter the marker shape (dots, lines, diamonds, etc.), they will effectively deter bird strikes if applied using the 2 x 2 Rule, meaning if separated by 50 mm either in horizontal rows or in vertical columns. Multi-paned glass is an effective visual marker that birds avoid if horizontal and vertical mullions create at most 100 x 100-mm (4 x 4-in.) subdivisions.
The height of marker treatment on any façade is critical. It must be 16 to 25 m (52.5 to 82 ft) above grade. The limits of treatment are associated with the prospective height of mature trees seen through or reflected off the glazing that provides an attractive illusion to birds. Exceptions to these limits occur when buildings are placed within ravines or at varying heights relative to different grades near bird-attracting vegetation seen through or reflected in higher heights or in the entire glazing. At these sites all or the glass above the reflected mature vegetation must be treated with protective markers.
Integrated building structures
Integrated and permanently installed building structures, such as recessed windows, awnings, sunshades, screens, grilles, mesh, shutters, louvers, decorative façades wrapping entire structures, and balconies or overhangs providing shading below their projections qualify as preventive bird collision applications. Each of these options reduce the amount of visual glass, mute reflections during certain times of day, and provide visual cues for birds to avoid the area. They can be used in retrofitting an existing structure, or as design features of new buildings. An example is the grille placed in front of the windows of the New York Times building in New York City.
Traditional insect screening placed over windows eliminate bird strikes by preventing a flying bird from hitting the unyielding glass surface while absorbing the force of the impact. Widely spaced net openings covering the outside of glazing can do the same, but caution is advised when selecting materials and mesh size and during installation to prevent birds from entering and becoming trapped between the netting and glass surface. These external net coverings also trap unwanted leaves and other debris, thus requiring continuous maintenance. With the exception of insect screening and similar netting, the collection of optional integrated structures reduces but does not eliminate the risk of bird strike casualties as long as some areas of sheet glass, no matter how small, are exposed in a façade.
Design
Additional considerations of where a building is proposed to be constructed must be examined to reduce the risk of bird mortality. Site locations increasing the risk of fatal bird strikes exist near natural avian habitat and along known migratory flightpaths. Research studies have repeatedly revealed the two principal features that best explain the number of birds dying from striking windows at any one location are the amount of sheet glass covering a building and the associated vegetation attracting birds to within the immediate vicinity of the window surface, within 10 m (33 ft).
