Kill the Lights, Save the Birds

by Valerie Blaine

Migratory birds have evolved over millennia to make round-trip journeys across continents and oceans. That a creature weighing as little as 0.35 ounces can navigate thousands of miles twice a year, is astounding. That it arrives safely and lives to do it again, is close to miraculous.

Birds face lots of challenges during their journeys. Predators, storms, and starvation are just a few. They have evolved to meet these perils, and most live to tell the tale – or at least to pass on their genes. But two modern-day challenges have popped up in the past century, and birds are ill-equipped to meet them: artificial lights and reflective buildings. These novel challenges have risen suddenly, in terms of evolutionary time. Birds haven’t had a chance to “catch up” and adapt to the sudden, new environmental hazards.

The death toll is staggering.

“Each year, an estimated 365 million to one billion birds die by smacking into reflective or transparent windows in deadly cases of mistaken identity, believing the glass to be unimpeded sky,” wrote Christine Hauser in The New York Times.[1] That’s a lot of birds.

While collisions kill birds directly, light pollution kills them indirectly. The majority of birds migrate at night, and the star-filled night sky is their version of Google Maps. [2] The ability to get their celestial bearings is critical to the success of their journey. Light pollution diminishes the ability to see stars and constellations. It also distracts with false signals from below.

Studies have shown that blinking lights, such as those atop communication towers and wind turbines, disorient birds. They fly aimlessly in circles, as dazed and confused as a Led Zeppelin fan on a good night. This needless flying depletes their energy at a time when they can least afford it. Their vocalization changes, too, and they are less able to use audible cues to keep track of each other in flight.

One of the most dramatic, unintended studies of this phenomenon is the 9/11 memorial in New York City. The Tribute in Light is a commemoration of those lost in the terrorist attacks of 2002. Two beams of light, each comprising 44, 7,000-watt xenon bulbs, shine skyward. When illuminated, the Tribute in Light is clearly visible in a 60-mile radius from Manhattan.

The message of the Tribute is important for our nation. Everyone who has seen the annual Tribute on September 11 says the emotional impact is profound. The biological impact, unfortunately, is devastating.

When the Tribute was in the planning stages, the New York City Audubon group anticipated the impact of the lights on migrating birds (September 11 falls in peak fall migration.) The Audubon group began working with the tribute’s organizers and worked out a plan. “When more than 1,000 birds are seen circling in the beams or flying dangerously low with frequent calling,” according to an article in Bird Watching Digest[3], the lights are turned off for twenty minutes.

Researchers got to work and set up radar and audio equipment to measure the effects of the Tribute lights. They collected data each year on September 11. In 2017, their work was published in the Proceedings of the National Academy of Sciences. The results were clear. Soon after the lights were turned on, thousands of birds were drawn to the beams, flying in circles and often circling dangerously low. They emitted frequent vocalizations. When the lights were extinguished, birds resumed their normal behavior, no longer flying in erratic circles nor vocalizing in stress. When the lights were turned on again, the behavioral disruptions re-appeared.[5]

The researchers estimate that by the time of publication, an estimated 1.1 billion birds had been affected by the Tribute in Light.[4]

Thankfully, few of us have 7,000-watt xenon bulbs illuminating our back yards. We can all help migrating birds, though, by turning off exterior lights at night. We can also encourage our elected officials and city planners to incorporate dark-sky friendly lighting in their building codes.

“Kill the lights, not the birds,” summarizes the issue nicely. Darkness is beautiful for stars, for birds, and all creatures great and small.

For more ways you can help, see …

[1] https://www.nytimes.com/2021/04/10/us/bird-migration-lights-out.html

[2] Dung beetles and seals as well. https://www.nationalgeographic.com/animals/article/stars-milky-way-navigation-dung-beetles

[3] https://www.birdwatchingdaily.com/news/science/study-september-11th-tribute-light-impact-birds/

[4] https://www.pnas.org/content/114/42/11175

[5] https://www.pnas.org/content/114/42/11175

On a routine walk to work in the city, it's not uncommon to have to step over dead birds that litter the sidewalk. These are the casualties of nocturnal migration, as millions of birds collide into lighted, reflective surfaces of buildings each night. Ken Walczyk shared these photos he took as he walked to the Adler Planetarium.