“Every year, millions of migrating birds cross the skies of New York City along one of the world’s busiest avian routes. Of these, up to 250,000 don’t make it. These unfortunates end up dead in the city’s streets, victims of collisions with brightly lit buildings.” – Jules Stewart, author of Migrating birds fall foul of New York’s bright lights.

The bright lights of Manhattan at sunset. Daniel Arranz/Shutterstock newyorkbirds.jpg

You may wonder how something as simple and normal as lights can harm birds and I’m going to explain why they are a big problem for them. Many migratory birds such as thrushes travel at night. The cooler, calmer night air lets them save energy as they fly, helping them stay hydrated and avoid tiring out too quickly. These birds travel long distances from the United States to Central America at night to avoid predators and conserve energy. Artificial lights, which are the lights created by humans, can attract large numbers of night-migrating birds from as far as 5 kilometers away and confuse their sense of direction. Birds are normally guided by moonlight and starlight, which are stable and give them reliable guidance, but the lights of buildings can confuse their direction. When they see city lights, especially tall and very intense ones they think they are landmarks or the sky. By getting stuck in the illuminated area and traveling in circles, many birds become exhausted, without enough energy to continue their journey and in confusion crash into windows and die instantly.

Wood Thrush, All about birds, Cornell labs of Ornithology. id

This disorientation caused by artificial lights goes beyond exhaustion and crashes. As some researchers explain, bright city lights can interfere with the three main orientation mechanisms birds rely on: “solar, stellar, and magnetic” compasses. For example, “artificial light may…interfere with the stellar compass, which forms when young birds identify the center of celestial rotation during their first spring” and use constellations to guide their path. With the increasing glow of urban areas, these constellations become harder to see, leaving birds vulnerable to losing their way. Additionally, artificial light can disrupt the magnetic compass by affecting a radical-pair process in the retina that helps birds detect Earth’s magnetic field. This interference, combined with the glare of intense lights that “bleaches the rhodopsin in their retina,” (Adams, C., Hernandez-Juricic, E., Bayne, E., & St. Clair, C., 2021) leaves birds unable to see dim celestial light or identify reliable landmarks. These compounded effects make artificial lighting a persistent and deadly hazard for migratory birds.

Birds flying around the iconic Flatiron Building in New York. Image: Shutterstock

“Migratory birds depend on cues from properly timed seasonal schedules. Artificial lights can cause them to migrate too early or too late and miss ideal climate conditions for nesting, foraging, and other behaviors.” (Darksky, 2023). Migratory birds depend on natural cues, like the length of daylight and temperature changes, to know when it’s time to start their journey. These signals help them determine the best time to fly, ensuring they find the best conditions for feeding, nesting, and surviving. But when we add artificial lights into the mix, it messes with their natural instincts. Bright lights at night can confuse the birds, making them think it’s earlier or later in the season than it really is. This could make them leave too early or too late. If they leave too soon, they might run into bad weather or not find enough food. If they leave too late, they could miss out on the best conditions for breeding or foraging.

It’s easy to forget how our actions affect the world around us, especially the animals that live in the same spaces. Migrating birds are just trying to survive, and something as simple as city lights is throwing them off track. By making small changes, like dimming our lights at night or designing buildings that are safer for birds, we can help make sure they have a better chance. It’s a simple fix for us, but it could make a world of difference for these birds and the future of wildlife.

References

Stewart, J. (2024, February 2), Migrating birds fall foul of New York’s bright lights, Geographical. 

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Adams, C., Hernandez-Juricic, E., Bayne, E., & St. Clair, C., (2021, December 15), Effects of artificial light on bird movement and distribution: a systematic map, Environmental Evidence. s13750-021-00246-8

Staff, (2023, November 13), Light pollution harms wildlife and ecosystems.

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