A sight unseen
Birds perish simply because they are unable to see glass on their flight path. According to ABC, “because of their small size and high-speed flight, birds hit glass and are usually killed or sustain injuries that will likely kill them.” More than 258 species, everything from hummingbirds to falcons, are documented victims of collision.
Glass reflecting skies or vegetation attracts birds, leading to collisions. Green habitats inside buildings with see-through façades, which is a growing trend, can also lure birds to their deaths. Glass corners or narrow glazed passages are other risk factors. Building strikes are second only to domestic cats as the most dangerous direct threat for avians.
Birds are also threatened by their migration patterns. Many travel along the densely populated ‘Atlantic Flyway,’ which hugs the U.S. eastern seaboard. “Located at the nexus of several migratory routes, New York City’s tall buildings with reflective glass pose a serious threat to over 100 species of migratory birds, some of which are experiencing long-term population declines,” according to the New York City Audubon Society. Chicago, which is located along the ‘Mississippi Flyway,’ is the most dangerous city in the United States for migratory birds. The Chicago Bird Collision Monitors (CBCM) recover about 6000 birds in a 4-km2 (1.5-mi2) area each year.
Game-changing glass
Bird-friendly architectural glass has been available for many decades, even though it has not always been marketed as such. This glass is visible to birds as it has bird-safe decorative pattern or a surface texture that breaks up continuous reflections.
The rule for these bird-safe patterns is based on research and testing. It is clear and simple, and also allows design professionals and glass manufacturers tremendous creative freedom. Known as the ‘2×4 rule,’ it stipulates glass patterns should be spaced no more than 50 mm (2 in.) apart vertically, or 100 mm (4 in.) apart horizontally (Figure 2). This is based on the findings that birds will not attempt to fly through openings that are less than 50 mm high or 100 mm wide. This means a wide range of designs, from timeless linear patterns to stylized nature-inspired motifs, can be employed in bird-safe glass architecture. Applied through a range of contemporary decorative glass technologies, including fritting, printing, etching, and carving, they can add originality and character to the building.
When creating bird-friendly glass designs, following the 2×4 rule is the best place to start. ABC also offers flight tunnel testing for bird-smart glass products. Spaces are limited and testing is performed in the spring and fall time only, making it best suited for standardized glass products with wider market appeal.
