The New York City Skyline at night. Photo: Adriano BIDOLI/CC BY-NC-ND 2.0
Many birds, including most songbirds, migrate at night. Exactly how these birds navigate through the night is a question that ornithologists are still trying to answer. Star maps and physical landmarks are among the resources that birds use, but a third, natural “roadmap” may be most closely related to the perils posed by artificial light. Birds are able to determine location and direction using the magnetic field of the Earth; they may actually be able to “see” these magnetic lines in the presence of the natural dim blue light of the night sky.
When point sources of artificial light, such as brightly lit skyscrapers and upward-facing beams, project into these birds' migratory airspace, this lighting may obscure the magnetic “guidelines” and/or disrupt the birds’ magnetic sense, causing them to deviate from their normal flight paths.
How Light Impacts Bird Collisions
The majority of collisions with buildings take place in the daylight, but the birds are drawn to these unsafe environments by night-time lights: the amount of light emitted by a building is a strong predictor of the number of collisions it will cause, more so than building height. The urban glow of cities along migration routes can actually cause birds to orient towards and stop over in cities. They may then be either injured as they flutter confusedly about the lights, or become exhausted and settle in inhospitable areas that make them more vulnerable to collisions.
When dawn comes and hungry birds look to refuel for their long journeys ahead, they encounter a confusing urban landscape full of glass windows and facades that reflect sky or habitat, often colliding as they seek refuge or escape.
Learn more about the effects of night-time lighting on bird migration in Bird-friendly Building Design, our joint publication with American Bird Conservancy.
Working toward Solutions
Because of the connection between artificial lighting and collisions, many programs to protect migratory birds from collisions have focused on reducing night-time lighting during migration—including the Fatal Light Awareness Program (FLAP), the Toronto-based conservation society that spearheaded the lights-out movement in 1993, and NYC Audubon’s own Lights Out New York Program, founded in 2005. Given New York City’s great size and huge number of artificially lit buildings, however, achieving an impactful level of consistent “lights out” participation by the City’s buildings has proved challenging.
Following the landmark passage of citywide bird-friendly design legislation in late 2019, NYC Audubon looks to shift its advocacy focus towards the creation and passage of legislation that would require a reduction in artificial night-time lighting during spring and fall migration. Such a law would save the lives of countless birds—and in reducing energy consumption, form a logical part of the City’s sustainability strategy.
Artificial Light Research
In order to gain a clearer scientific understanding of the exact relationship between regular urban night-time lighting and bird deaths, NYC Audubon collaborates on research designed to better understand how night-time lighting affects birds that are migrating through the city, and how it may contribute to collisions. Our ongoing research with academic partners Cornell Laboratory of Ornithology and the University of Delaware correlates the density of migratory birds passing through the City with the intensity and quality of night-time artificial light. Comparison of these findings with our collision data will allow us to understand the interaction between artificial light and the bird deaths caused by building glass—and point us toward solutions.
NYC Audubon volunteers monitor the Tribute in Light each year for birds stuck circling in the Tribute’s powerful beams. Photo: NYC Audubon
The Tribute in Light
NYC Audubon staff and volunteers have monitored the Tribute in Light memorial since 2002 to ensure that while we honor those lost to us on September 11, 2001, unnecessary harm does not come to thousands of migrating birds who are attracted to the Tribute’s powerful lights and get stuck circling within its beams. This has helped advance our understanding of the impacts of artificial light on night-time migrating birds.