How to help birds avoid hitting buildings
A big, glass-covered building makes a dramatic addition to a cityscape. It is a statement of human ingenuity and engineering. However, these buildings wreak havoc on birds. An estimated one billion birds die in collisions with buildings in the US every year. The majority of these collisions occur in the daytime, especially during the seasonal migrations of spring and fall, when more birds are moving between their regional territories.
Surprisingly, smaller buildings have an even greater impact. While most people consider bird collisions with glass to be an urban phenomenon involving tall, many-windowed skyscrapers, the reality is that 56 percent of collision mortality occurs at low-rise buildings of four stories or less, 44 percent at urban and rural residences, and less than one percent at high-rise buildings, according to the US department of Fish and Wildlife. This is because shorter buildings are most common and are at the same level as the vegetation, making them more likely to be in the flight path of more birds.
The reason birds collide with glass comes down to the difference between how humans and birds see the world. Contrary to a popular myth, neither humans nor birds “see” glass; anyone who has ever walked into what they thought was an open door will understand this concept. People are conditioned to understand that glass is transparent and/or reflective. Birds do not perceive glass, which creates a lethal illusion of open airspace.
The majority of collisions occur during the day, when birds can see reflections of the landscape in the glass, such as clouds, the open sky, vegetation, or the ground, or birds see through the glass to real or perceived habitats like potted plants or vegetation inside the buildings. During inclement weather, especially overcast or foggy conditions, migrating birds can be attracted to lighted buildings. This results in collisions and exhaustion. The birds may become entrapped in parts of the structure or continually try to find a way through the glass, burning up precious energy reserves.
Birds are critical to ecosystems. Those like crows and vultures scavenge carcasses, reducing the spread of diseases such as rabies and distemper. Some disperse seeds, spreading plants into new areas. Birds such as hummingbirds help pollinate plants. Predators like hawks and owls help keep the mouse and rat population in check. Others eat millions of mosquitoes and biting insects each year. Birds also serve as an important food source for other animals.
Starting in April 2018, a group of Yale faculty, staff, students, alumni, and citizen scientists began monitoring bird collisions at Edward P. Evans Hall as part of a wider case study to monitor bird strikes on campus and develop a plan to reduce collisions. The building features roughly 130,000 square feet of exterior glass; a courtyard with six honey locust trees; and multiple design features linked to fatal bird collisions, such as transparent walkways and unobstructed, reflective windows abutting bird habitat. From April 2018 to April 2022, at least 419 birds were killed and at least 19 birds were injured or stunned due to collisions with the building. These birds represent at least 56 species, including multiple species of conservation concern.
This shows the impact that human-created obstacles are having on all species of birds. Only free roaming, outdoor domestic cats are doing more damage to these populations, as published in the journal Nature Communications.
A number of steps can be taken to minimize bird collisions. Simply designing or retrofitting buildings to minimize elements that have been proven to confuse birds, including changing the type of glass used, adding awnings, shades and shutters to eliminate reflections, and adding screens and netting can reduce collisions by up to 90 percent.
Another factor is night time lighting. Reducing or eliminating excessive and unnecessary nighttime illumination will not only help birds, but it also reduces light pollution and saves energy. The Fish and Wildlife service states that reduced lighting power can be accomplished using lighting control strategies that extinguish or dim interior lighting when it is unneeded, such as when the building is vacant, during the workday when a space is unoccupied, or when natural lighting is adequate. Exterior lighting can also employ motion sensors and light downshields resulting in cost savings with only modest initial investment.
For individual homeowners, taking steps on the exterior of windows will be most effective. These treatments usually involve some form of visual disruption, such as lines or dots, that the birds can recognize as a barrier and avoid.
For more information on bird conservation, visit the American Bird Conservancy at abcbirds.org
