Bird Migration and Light Pollution: Lights Out at Home

Most songbirds migrate at night, and artificial light pulls them off course. Bright lights draw migrating birds toward buildings, where they circle until they are exhausted or fly into windows, especially on cloudy or foggy nights. Turning off unneeded outdoor lights and closing your blinds from late evening until dawn during spring and fall migration is one of the simplest ways to help them from home.

It costs nothing, it saves a little electricity, and it matters most on a handful of peak nights each season. Here is why light causes the problem, when the risk is highest, and a checklist for your own house.

Why lights draw migrating birds

Warblers, thrushes, vireos, orioles, tanagers, cuckoos and many sparrows travel mainly at night. The air is cooler and calmer, there are fewer predators, and the daylight hours are free for feeding. Our guide on why birds migrate at night explains more.

Night migrants find their way using the stars, the Earth's magnetic field, the position of the setting sun and landmarks below. Bright artificial light can disorient them and override those cues. On clear nights most birds pass high overhead with little trouble. When low clouds, fog or drizzle hide the stars, birds fly lower and are far more likely to be drawn toward bright lights and the glow over towns and cities.

Once they are pulled in, three things go wrong:

• They circle. Birds caught in the light around a building or tower can fly around it for hours, burning fat they need for the journey.
• They collide. Birds hit lit windows at night, and many more hit glass the next morning while searching for food among buildings.
• They land in the wrong place. Birds that come down in a brightly lit area at dawn may find little food or cover and more glass and cats.

Do houses matter?

A single porch light is tiny compared with a lit office tower. But low buildings, houses included, account for a large share of window collisions overall, simply because there are so many of them. Lights left on near windows bring birds to exactly the glass they are most likely to hit, and every outdoor light adds to the sky glow over a neighborhood.

When the risk peaks

Timing varies by region. Spring migration reaches the Gulf Coast and the Southwest weeks before it reaches the northern states, and fall runs the other way. Within those windows, most birds move on a relatively small number of nights, when the winds help them along.

The most dangerous nights for lights are big-flight nights that turn cloudy, foggy or rainy, because birds already aloft drop lower. Most night migrants take off within an hour or two after sunset, and flights continue through the night before tapering off toward dawn, so the late-evening-to-dawn hours are the ones that count.

What Lights Out programs are

Many US cities now run Lights Out programs during migration. They ask building owners, businesses and residents to turn off or dim nonessential lights at night, especially decorative lighting on tall buildings and lights in empty offices, during the spring and fall migration seasons. Many programs focus on the hours from late evening until dawn.

You don't need to sign up for anything to take part. The same idea works at home: keep the dark hours dark while the birds are passing over. If your city or town has a program, following its dates is an easy way to know when to start and stop.

Keeping a dark yard safe

Lights out doesn't mean stumbling around in the dark. The goal is to cut light that nobody is using, not the light you need. A motion-sensor light over the steps gives you full brightness when you walk out and stays off the rest of the night. Low, shielded path lights that point at the ground can stay on while decorative uplights and all-night floodlights go off.

If a neighbor's floodlight shines across your yard all night, a friendly conversation during migration season, or a suggestion to try a motion sensor, often goes further than you expect.

A home lights-out checklist

Outside

1. Turn off decorative lighting overnight during migration: uplights on trees and walls, string lights and landscape lights.
2. Put security lights on motion sensors, so they are dark most of the night and bright only when needed.
3. Aim lights down. Use shielded fixtures that light the path or the steps, not the sky or the side of the house.
4. Use timers so porch and garden lights switch off at bedtime instead of burning until morning.
5. Choose the dimmest light that does the job. A softer light on the steps is often safer to walk by than a glaring floodlight anyway.

Inside

1. Close blinds and curtains at night, especially on large windows, glass doors, stairwells and upper floors.
2. Turn off lights in empty rooms, and use lamps placed away from windows in the rooms you are using.
3. Don't leave lights on all night for a house that looks lived-in; use timers that switch off later in the evening.

On the glass

1. Mark your worst windows on the outside with dots, tape or cord spaced no more than about 2 inches apart. That helps birds by day as well as by night. Our guide on how to stop birds hitting windows covers the options.
2. For Bird Migration and Light Pollution: Lights Out at Home, treat hazardous glass with a maintained exterior collision-prevention solution and inspect the actual flight path. Feeder distance alone is not a universal safety rule.

What else helps migrants passing through your yard

A dark yard at night is half of it. The other half is giving tired migrants a good place to refuel by day.

• Native plants. Native trees and shrubs host the caterpillars and insects that warblers and vireos eat, and fall berries from dogwood, viburnum and spicebush fuel thrushes and catbirds on their way south.
• Leaf litter. Leaving leaves under shrubs gives thrushes, towhees and sparrows insects to find.
• Water. A shallow bird bath draws migrants that never visit a seed feeder.
• Cats indoors. Exhausted migrants spend a lot of time low in shrubs and on the ground, where cats catch them easily.

If you do find a stunned bird below a window, our guide on what to do with an injured bird explains how to keep it safe until it recovers or reaches a rehabilitator. And to know when the next wave is coming, see when birds migrate in the fall.

Lights out doesn't need to end with migration. Keeping outdoor lighting low all year helps moths and other night insects that birds feed on, and it keeps the night sky visible from your own backyard.

Sources and editorial verification

Editorial boundary for Bird Migration and Light Pollution: Lights Out at Home: Nightly migration intensity changes with weather and location, while window risk requires effective exterior glass treatment rather than the retired 3-or-30 distance shortcut; Migration timing and abundance are probabilistic and location-specific; live forecasts and current regional data supersede fixed calendar dates. Check linked sources and the responsible local authority again before acting because product documentation, disease conditions, wildlife rules and seasonal observations can change.

• Cornell Lab of Ornithology and Colorado State University — checked for nightly migration forecasts.
• Cornell Lab of Ornithology — checked for migration terminology.
• U.S. Fish and Wildlife Service — checked for hidden and delayed window-collision injuries.
• Cornell Lab of Ornithology — checked for window-collision placement rule.
• Cornell Lab of Ornithology eBird Science — checked for modeled seasonal abundance.
• Cornell Lab of Ornithology — checked for species identification.

Written by the Backyard Birdcam team with AI assistance. Found something we got wrong? Email shop@smarternewsnow.com and we will fix it. How we write our guides.