Birds trapped in the light beams of the 2016 Tribute in Light Memorial. Photo: NYC Audubon
Birds trapped in the light beams of the 2016 Tribute in Light Memorial. Photo: NYC Audubon

Tribute in Light Monitoring

Throughout modern history, clouds of birds have been observed fluttering around large lit-up structures, such as lighthouses, bridges and skyscrapers, including the Empire State Building and the Statue of Liberty—and most recently, the Tribute in Light Memorial. While birds are not always deceived and harmed by lighted structures, in certain circumstances, the harm can be devastating. 
 
As part of our job as guardians of migrating birds, 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. Night-migrating songbirds can be attracted in huge numbers to the Tribute’s powerful light beams, becoming exhausted and injured during the all-night event. 
 

 
In cooperation with partners Michael Ahern Production Services and The National September 11 Memorial & Museum, we prevent migrating birds from coming to harm by cooperatively shutting off the lights for short periods of time when too many birds become “trapped” in the light beams.
 
 Learn about becoming a volunteer for Tribute in Light monitoring and other community science programs here.

In addition to ensuring the Tribute is safe for birds, NYC Audubon collaborates with the Cornell Lab of Ornithology to further our understanding of artificial light’s effects on birds. Our research at the Tribute has demonstrated that the twin beams can attract bird densities up to 150 times higher than when the lights are not on.



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Perfect Storm
Over the many years of our monitoring program, it has become evident that a specific combination of circumstances can create a “perfect storm” for migrating birds during the Tribute in Light. When northwest winds produce a heavy migration flight and this coincides with a low cloud ceiling, birds can become trapped in the Tribute light beams in huge numbers. 
 
The evening of September 11, 2010, was one of those nights: thousands of birds were drawn to the lights and "trapped" on multiple occasions. Similarly, in 2015 the lights had to be turned off a record eight times to allow thousands of birds to migrate safely over New York City. Most years, it is necessary to turn off the lights at least a few times during the evening, in order to let migrants disperse and continue on their way. 
 
The images in the graphic below, showing concentrations of birds as detected by radar, were taken 20 minutes apart during the 2015 Tribute in Light. The low density of birds with the light beams turned off (left) is striking compared to the high concentrations present when the lights were on (right). These images were included in joint research by NYC Audubon and the Cornell Lab of Ornithology1.
 
Published Research Cited
1. Van Doren, B. M., Horton, K. G., Dokter, A. M., Klinck, H., Elbin, S. B., & Farnsworth, A. 2017. High-intensity urban light installation dramatically alters nocturnal bird migration. Proceedings of the National Academy of Sciences, 114:11175-11180.