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Billions of birds undertake migratory journeys each spring and fall. Most of these spectacular movements go unseen, occurring under the cover of darkness.
A new study published in the Proceedings of the National Academy of Sciences provides some of the most compelling evidence yet that artificial light at night causes radical changes in the behaviors of migrating birds.
“We found that migrating birds gather in large numbers because they’re attracted to the light,” Benjamin Van Doren of Oxford University, a lead author of the study, said in a statement sent to the press. “They slow down, start circling, and call more frequently. They end up burning energy without making any progress and risk colliding with nearby buildings or being caught by predators.”
Scientists from the University of Oxford, the Cornell Lab of Ornithology, and New York City Audubon studied migrant bird behavior over seven years in a unique setting — the Tribute in Light in New York City, held to commemorate the September 11, 2001 terrorist attack. Two beams of light – each with 44 xenon bulbs of 7,000 watts — rise into the night sky, mirroring the twin towers of the World Trade Center where nearly 3,000 lives were lost.
“This was a rare opportunity to witness the impact of powerful ground-based lights on nocturnally migrating birds,” says co-lead author Kyle Horton, now with the Cornell Lab, but working at the University of Oklahoma during the study. “This analysis would not have been possible without the help of tribute organizers.”
Well before the results of the study highlighted the effects of the installation, New York City Audubon reached out to the original tribute organizers, the Municipal Art Society, to let them know about the impacts of artificial light on migratory birds. In 2002, the two organizations worked together to develop a protocol to save the affected birds. The tribute lights are turned off for approximately 20 minutes when more than 1,000 birds are seen circling in the beams or flying dangerously low with frequent calling. The National September 11 Memorial Museum, which took over as tribute organizers in 2012, continued this practice.
These brief interludes of darkness during the nightlong tribute provided a unique opportunity for the scientists to quantify changes in bird behavior in several ways during the alternating periods of light and darkness.
“We had more than 20 wonderful volunteers on the ground counting birds to confirm what was happening in the beams,” says co-author Andrew Farnsworth at the Cornell Lab. “We also used remote sensing tools, including data from local National Weather Service radars, to understand the density and movements of the birds. Acoustic monitors recorded call notes and captured the vocal behavior of birds in the beams. And we ran computer simulations to try to better understand the dynamics of the patterns we were observing.”
Images above were taken 20 minutes apart during the 2015 Tribute in Light and show concentrations of birds on radar with light beams turned off (left) and turned on (right). Figure adapted from “High-intensity urban light installation dramatically alters nocturnal bird migration” in Proceedings of the National Academy of Sciences, September 2017.
When the tribute was illuminated, the study’s authors found that densities of birds over lower Manhattan could reach 60 to 150 times the number that would typically be found in the area at that time. The concentrating effects of the intense light on the birds reached as high as four kilometers. The impact on birds was consistent even on clear nights. Many previous studies focused on the dangers posed by artificial light on nights with poor visibility. When the light beams were turned off, the birds dispersed within minutes to continue their migrations.
Although Tribute in Light provided a way to measure a specific instance of light attraction, bright nighttime lighting poses problems for birds, even in rural areas. The study’s authors point out that one solution is relatively simple.
“We recommend building lights be turned off for as much of the night as possible, but at least from midnight to dawn during migration season,” says study co-author Susan Elbin of New York City Audubon. “This is true for areas around homes as well as other brightly-lit areas such as sports stadiums, construction sites, offshore oil rigs, and large buildings. Migrating is already hard enough for birds without this added danger from artificial light at night.”
This study was conducted with support from the National Science Foundation, Leon Levy Foundation, Marshall Aid Commemoration Commission, Cornell Lab of Ornithology Rose Postdoctoral Fellowship, and NASA.
Photos from above: Migrating birds circle through the light beams during the 2017 Tribute in Light, by Kyle Horton; 2015 Tribute in Light study, provided.
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I have long argued that Adirondack Park municipalities should have light-pollution abatement laws, and perhaps the APA should require them. The dark night skies of the Adirondacks—striking in nighttime satellite images—are as much a valuable natural resource as are our clean air and pristine waters. I have read that fully half of the world’s population cannot see the Milky Way because of light pollution. We are lucky to have our beautiful starscape.
And I ask my neighbors in the Town of Webb and elsewhere: do you really need those halogen security lights blazing all night? If you must have them, could you at least install motion detectors or some other way of keeping them off when not needed?
There are many models for light-pollution-abatement laws around the country. Adirondack communities should study them and adopt ones appropriate for our unique situation.
People move up to the mountains from the city and they bring their habits with them, ie…lights left on at night for one. When I go up to see mom and dad in the Adirondacks one of my things is to stand outside in the dark and look up at the stars. There used to be just a field across the street then the lot was sold and a house went up and when Condra died his house was sold and a new owner took over who just cannot seem to get enough light outside at night when she comes up. I remember those nights when I didn’t have to have my stargazing disrupted by lights left on by neighbors who evidently are afraid of monsters why else would leave lights on at night? Some of the locals do the same….leave their porch lights on and why this desire for streetlights in small Adirondack hamlets when you have towns outside of the park who have no streetlights at all? Some towns actually fight to keep streetlights out of the picture.
I have known that the birds get screwy from all of the lights at night and I have known it is not good, but who do you talk to about it? Who really cares? Our elected officials? The electric companies? Them’s like talking to brick walls. I know your angst Tom.
Companies touting security say the more light, the better. But it is wasted energy unless there are criminals about. Virtually any outdoor lighting type has alternative designs that only shine downward. Light shining upward is wasted. Properly designed lighting saves wattage while minimizing light pollution.