There are four general types of threats the built environment poses to birds. These threats, which can result in fatal collisions, are reflectivity, transparency, a beacon effect and interior illumination. However, by adjusting a structure’s glazing and its interior and exterior lighting features, these threats can be mitigated. This post highlights some of the common solutions used by designers to make the built environment safer for birds.
When designing a site, local ecological features should be taken into consideration, and bird habitat or stopover locations should be documented. It is also advisable to consult with an ecologist or bird specialist to accurately take inventory of the bird species and habitats.
Avoid design concepts which require transparent barriers on the site, whether these are fences, guard rails or enclosed passageways. If these transparent barriers cannot be avoided, use bird-safe glazing strategies to reduce the number of collisions they will generate. Designing angled, glazed surfaces between 20 and 40 degrees from the vertical will cause the building to reflect the ground instead of vegetated spaces from a wider range of angles. While not perfect, this can be a valuable strategy for large glazed surfaces, particularly if they are designed with elements that block reflections from the sides of the surface.
When cladding a building in reflective opaque materials, the dangers of reflectivity can be reduced by creating curvilinear facades. Curvilinear or irregular reflective surfaces have been shown in case studies to pose less risk to avian species as their surfaces will warp the reflections to a point where birds no longer recognize them
Window patterning is also an effective bird deterrent and can be accomplished through several different techniques. These techniques include screen printing, roller printing, fritting, embedded filaments, sprayed enamel, adhesive materials and flush screens. A general rule of thumb for custom glazing developing is the 2×4 rule. This rule is based off the dimensions of songbirds, and states that any horizontal pattern should have spacing no more than 2” and any vertical pattern should have spacing no more than 4”.
No pattern is 100 percent effective, but efficacy is increased by tightening the pattern and moving it as close to the exterior surface of the glazing as possible. Ideally the window treatment would be located on the outermost surface of the glazing to avoid being obscured by high contrast reflections. UV treatments can be effective for some bird species, but others are less sensitive to light on the UV spectrum.
The most straightforward lighting strategy that can be used to reduce bird fatalities is simply turning the lights off at night. This is not always an option, so an additional consideration is to reduce the amount of light projected into the sky. If there is going to be persistent lighting on-site, it should be shielded and directed downward rather than skyward.
Other Effective strategies include:
• Exterior shading devices
• Offset exterior screens
• Exterior bird netting
• Window screens
The following information is from a literature review performed by Cuningham Group Researcher Dustin Schipper summarizing reports on bird-safe design, currently available regulations and some of the basic information used to develop them.