The following is a guest post by Em Merrick, an intern with the Digital Resources Division of the Law Library of Congress. They are a recent graduate with an M.F.A. in creative writing from West Virginia University.
Yellow-breasted Warbler. Color engraving by R. Havell, after drawing by John J. Audubon. Library of Congress Prints and Photographs Division. /hdl.loc.gov/loc.pnp/cph.3b52364
As the month of November ends, so does the annual fall migration season for birds in North America. According to the Cornell Lab of Ornithology, the adult breeding bird population in the United States and Canada has been reduced by almost 3 billion since 1970, a nearly 30% decline.
Although the actual impact is difficult to measure, a 2005 study published by the U.S. Forest Service estimates that 500 million to 1 billion birds die annually from human-driven causes, with a significant number of those coming from collisions with buildings. The American Bird Conservancy that up to one-third of bird species in the U.S. are affected by collisions. Even the most conservative estimates place the number of collisions in the hundreds of millions.
The most significant contributor to bird collisions is glass. Many modern buildings use glass in their construction; however, it poses a problem for birds: depending on the time of day, glass can appear either transparent, reflective of the environment, or dark, mimicking an opening in the façade that is safe to fly through.
John Hancock Center. Bill Engdahl. 1969. Library of Congress Prints and Photographs Division. //hdl.loc.gov/loc.pnp/ppmsca.54501
Large cities like Chicago, home to numerous skyscrapers and crowded streets, are particularly hazardous for birds. Bad weather and wind conditions can lead to mass collision events with large glass buildings, such as the McCormick Place Lakeside Center.
Public concern about bird safety is nothing new among Americans. The Migratory Bird Treaty Act of 1918 (40 Stat. 755), which protects certain birds from being hunted, killed, or transported unlawfully, was codified at 16 U.S.C. 703-712. Yet, it does not address bird safety in the context of buildings and new technologies, an issue that was well-documented even at the time the act was passed.
In the United States, before the advent of glass skyscrapers, the biggest threat to migrating birds was artificial light. From oil-powered lighthouses to the electrified Statue of Liberty, the mid-to-late 19th century saw the rise of technological achievements that made lighting up the night sky a possibility, but also threw bird populations into chaos.
Richard Mahler (5) is the Fire Island School’s youngest pupil and lives the farthest away. His father is the lighthouse keeper and, since the lighthouse is about four miles away, school is a long ride by jeep/ World Telegram & Sun photo by Roger Higgins. 1952. Library of Congress Prints and Photographs Division. //hdl.loc.gov/loc.pnp/ppmsca.09037
As cities like New York became perpetually lit, birds—particularly nocturnal birds—were pulled away from traditional migratory routes into direct contact with buildings, increasing reports of bird collisions. Conservationists and ornithologists at the time advocated for reduced light pollution, and many continue to do so now through programs like Audubon’s Lights Out.
In recent years, state and municipal legislation has sought to curb bird collisions through implementing “bird-friendly” building requirements, such as:
- In 2020, the city of Madison, Wisconsin, passed general ordinance 129 titled “Bird-Safe Glass Requirements,” which went into effect in October that same year. It requires the treatment of glass facades, skybridges, and at-grade glass features. An appeal opposing the ordinance was filed by the Wisconsin Institute for Law & Liberty (WILL), representing several local construction and real estate companies; however, the law was upheld.
- New York City, New York published its own bird-friendly building requirements after adopting Local Law 15 of 2020, which took effect in January 2021. It addresses known bird hazards such as highly reflective glass, prescribes safe fly-through conditions for birds, and provides examples of bird-friendly materials such as glazing treatments and visual markers.
- Washington, D.C., passed the Migratory Local Wildlife Protection Act of 2022, with similar requirements to those in New York City, but it allows exceptions for historical landmarks. The act went into effect in October 2024.
- The state of Maryland passed the Sustainable Buildings Act of 2023, which specifically regulates the glass in state buildings (classified as those with 51% or more Maryland state funding). The act is unique in its requirements for shielded nighttime lighting, which reduces glare and may assist nocturnal birds.
- Two building developments in Virginia have been designed as bird-friendly buildings through Fairfax County’s proffer. A proffer is a legal agreement that happens when “the developer agrees to minimize the impacts on the surrounding neighborhoods and the county by providing funds for amenities such as road improvements, schools, parks, and more.” (Bigger.)
The American Bird Conservancy estimates that 46% of annual bird deaths are due to building collisions with homes. (Bird-Friendly Building Guide. American Bird Conservancy. p. 9.) Bird deaths due to collisions are avoidable, and there are many preventative measures homeowners can take to protect their local bird populations:
- Add insect screens or decals to the outsides of windows to reduce their reflectiveness. When applying decals, follow the 2”x4” rule, aka place them no more than 2 inches apart vertically, and 4 inches apart horizontally.
- Place bird feeders closer to windows. This will encourage birds to slow down before impacting with glass.
- Keep lights off at night and draw shades during the day.
- Participate in local Lights Out programs to help migrating birds and reduce light pollution.
For further reading on birds, law, and conservation from the Law Library of Congress:
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