Katherine Chen, Senior Manager of Community Science & Collision Reduction | October 8, 2024  

At 7pm on September 11, 2024, NYC Bird Alliance staff arrived on the roof deck of the Battery Park Garage, where 88 high-intensity lights were set up to form two twin beams. This luminous memorial is an annual display, shining from sundown on 9/11 to sunrise on 9/12 in remembrance of those who lost their lives during the terrorist attacks at the World Trade Center on September 11, 2001. 

Since the Tribute began in 2002, NYC Bird Alliance has partnered with the September 11 Memorial & Museum and Michael Ahern Product Services (MAPS) to ensure that that memorial is able to honor lives while also keeping birds safe. We are grateful for this continued partnership that demonstrates what amazing solutions are possible when we work together as a city. 

Around 70% of bird species are migratory and around 80% of those birds migrate at night. Artificial light at night attracts these birds into the City and disorients them. We see an extreme example of this on the night of 9/11. As the twin beams shine throughout the night, small, white, shiny specks can be seen twirling around in the lights. These white specks are birds that have been drawn to the lights and become “trapped” circling within them.

On nights when large migration pulses pass through NYC and under certain weather conditions likely to lead to bird collisions, thousands of birds may gather in these beams and, without intervention, exhaust the energy they need to continue on their migratory journey. In one particular year, we had to turn off the beams eight times to let "trapped" birds escape the lights.  

To prevent unnecessary harm to birds -- and conduct important collaborative research into light's effects on bird migration -- NYC Bird Alliance partners with MAPS to closely monitor the lights and turn off the lights when needed. Volunteers monitor both beams starting at 8pm on 9/11 until 6am on 9/12, counting how many birds are circling the beams every 20 minutes. 

If the number of birds exceeds a critical threshold of 500 birds per beam (or 1,000 birds total), or numerous birds are observed flying low in the beams, we ask the Tribute organizers to turn off the lights for 15-20 minutes to allow the birds to reorient themselves and disperse. 

Weather forecasts predicted fair weather with mostly clear skies for the night of 9/11, and BirdCast forecasted “medium” migration intensity, so we were hopeful for sparse bird activity in the lights but were prepared for a busy night. 

This all-night event was attended by NYC Bird Alliance board members, volunteers, members of the press, and Dr. Benjamin Van Doren, a researcher from the University of Illinois Urbana-Champaign who set up three thermal imaging cameras to record bird movements at the southern beam. 

8pm - the first group of volunteers began their first counts, with few birds in the immediate vicinity. All counts in the first two hours were in the single or double digits.

10pm - the number of birds circling the beams rapidly increased and birds began flying low in the beams.

10:20pm - many birds could be seen flying low and we also heard several flight calls from the birds trapped. Observing this, NYC Bird Alliance asked for the lights to be shut off for the first time. 

10:28pm - the lights were powered down for 15 minutes. As a result, we stopped hearing flight calls. Using a handheld thermal imaging camera (a camera that can record differences in heat, essentially allowing us to see in the dark) to record one of the beams, we were able to capture the birds’ movements as they came out of the trance. Within less than two minutes of the lights going out, the birds had completely cleared from the skies overhead!

10:45pm - the lights were turned back on at 10:45pm. The thermal imaging camera showed that the skies were all clear immediately prior to the lights going back on. Once lit again, a few birds were spotted circling high in the beams a couple minutes later. 

11:20pm and 12:08am - The lights went off for a short period at those times due to bird activity.

12:28am-6am - Minimal bird activity observed. There were a few moments throughout the night when numerous birds were flying low and vocalizing, but luckily after a few minutes they moved back higher or escaped the beams. Therefore, the lights did not need to be turned off again. 

While the main goal of the counts is to determine how many birds are circling the lights and whether the lights need to be temporarily turned off, we were also curious about which species were present. Identifying birds while they’re flying in the lights is difficult, but NYC Bird Alliance volunteers were able to identify several. 

As we welcomed the sunrise and packed up to return home for some much-needed rest at 6am, a question still remained: did the Tribute lights impact collisions in downtown Manhattan the following morning? Artificial light at night draws birds into the city where, come morning, when they are searching for areas to rest and refuel, they are forced to navigate a dangerous and confusing environment where they are susceptible to colliding with reflective and transparent glass. This is a major threat to birds and over a billion birds are killed from collisions every year in the U.S. alone. 

Thankfully, because we’re able to turn out the lights to allow the birds to disperse when they’ve congregated in the beams in high densities, we have never seen an associated increase in the number of collisions found by our Project Safe Flight collision monitors at nearby buildings in downtown Manhattan the following morning. This remained true this year and none of our volunteers found more birds than would’ve been expected if the lights had not been on. 

The Tribute in Light memorial is a stark reminder of the impact of artificial light at night on nocturnal migratory bird behavior. The Tribute, however high-profile and visible it may be, only occurs once a year. Lights emanating each night from many individual buildings, and the overall urban glow of New York City, draws birds off their migratory path on a daily basis during the spring and fall.

We can reduce artificial lights' impact on birds: NYC Bird Alliance is actively advocating for Lights Out legislation to curb the use of nonessential lights at night and protect migratory birds. 

Together with our partners at the Lights Out Coalition, we are championing a Lights Out bill, Intro 0896, introduced this year by Council Member Francisco Moya in the New York City Council. This critical legislation would require privately owned commercial and industrial buildings to turn off their nonessential lights at night, reducing our city's artificial light pollution that is harmful to both birds and people! As of this writing, it has 16 co-sponsors but needs 34 for it to pass.