Night Flights: Light Pollution Threatens Songbird Migration

Darkness creeps across the sky in swaths of indigo. As stars emerge from dark, I spot the blue glow of the constellation Orion and the flicker of Sirius, the brightest star. Wispy clouds float past the half-moon like a steady stream of gauze. The warm light of Mars appears, and the Big Dipper rises above rooftops. I peer up — watching, waiting. I am still, and in stillness I notice the Earth moving.

A thin V-shape traverses the sky, fading quickly into the clouds. Another follows, tracing a subtle path, barely illuminated. I squint my eyes; the shape looks like a large bird. Do birds migrate at night, I wonder. Later, I learn that they do. Birds migrate by the light of stars and the moon.

In one of Earth’s largest yet rarely witnessed phenomena, hundreds of thousands — even millions — of birds migrate across North America on any given night in spring and fall. As air cools at dusk, the atmosphere becomes calm enough for small songbirds such as warblers, thrushes, sparrows, and tanagers to navigate. The darkness also conceals these tiny travelers from the keen eyes of falcons, hawks, and other predators.

Magnolia Warblers that crashed into building in Galveston, Texas. Photo by Josh Henderson

But light, the very thing that guides songbirds across continents, now also misguides them. Light pollution from urban areas casts a wide and far-reaching glow, drawing birds off their paths and into cities, where many crash into buildings and windows. Hundreds of millions of birds die in building collisions each year. During peak migratory seasons, one building can kill hundreds of birds nightly. In Galveston, Texas, 395 songbirds fatally crashed into one brightly-lit building in a single night. Come morning, bodies of warblers and tanagers littered the sidewalk.

Photos: Bruce LePard

Seeing these gruesome images, I think of Rachel Carson, who was so moved by poisoned birds falling from trees in her friend’s yard that she exposed the pesticide DDT’s harmful effects in her famous book Silent Spring. In 1972 the U.S. banned DDT—a decision that brought Bald Eagles back from the brink of extinction. If Carson saw the lifeless bodies of small birds struck mid-migration, she surely would call on us to dim our urban brightness.

Simply turning exterior lights off during peak migration keeps birds safe on their journey. And one group is already inspiring action: BirdCast creates live bird migration maps using radar technology and predicts peak migration times based on weather patterns. In some cities, like Dallas and Houston, you can even sign up for migration alerts that inform you when to turn out your house lights and protect passing birds.

This is a live migration map by BirdCast from the night I saw migrating birds in Durham, NC. You can see the movement of birds towards that area. Click on image to enlarge.

Straight lines represent migration paths. The yellow represents light pollution from cities. Credit: Cabrera-Cruz et al. 2018 Click on image to enlarge.

The toll of light pollution will only heighten if we do not act. Scientists find that levels of artificial light are highest along migration passageways. And light pollution increases about 2% each year. That may not sound like a lot, but this growth accumulates over the years, eventually creating a stark change. Light pollution has risen so steadily since the 19th century that one third of the human population can no longer see the Milky Way.

The Milky Way.

Many animal and plant life cycles—the hum and rhythm of daily life—are guided by light. We live in circadian rhythm. And I think there is something wonderous in this connection life shares—all these instinctive responses to the sky, the change of light from night to day, the cycles of moon that draw tides and encourage corals to spawn.

Life began, formed, and evolved to respond to Earth’s lucent patterns. When we obscure those patterns, we not only disrupt billions of migratory birds’ life cycles but also our own lives. By turning out the lights when and where we don’t need them, I hope we may bring pockets of darkness back. For darkness is like silence, like stillness.

Dimming our artificial brightness, we realize the universe is shining — and the birds are flying.

Kendall Jefferys – Rachel Carson Council Presidential Fellow.
Kendall Jefferys is a Rachel Carson Scholar at Duke University and a dual major in Environmental Science and English. She initiated the RCC Coasts and Ocean Program. Ms. Jefferys has been named a Rhodes Scholar for 2021. [email protected]


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