Light Pollution Harms Migratory Birds: How to Help

Light pollution harms migratory birds by disrupting the celestial cues, daily rhythms, and seasonal behaviors that guide their lives. Each year, billions of birds travel between breeding and wintering grounds, often at night. Artificial light from buildings, streetlights, bridges, stadiums, and homes can draw these birds away from their routes, cause exhaustion, and increase collisions with glass. The National Wildlife Federation’s guidance on reducing light pollution offers additional information about protecting migrating birds.

Essential Concepts

• Night-migrating birds use stars and other sky cues for orientation.
• Artificial light can attract birds into cities and toward reflective glass.
• The most effective actions are turning off unnecessary lights, shielding fixtures, closing blinds, and reducing window reflections.
• Bird-friendly lighting helps people while limiting harm to wildlife.

Why Birds Migrate at Night

Many songbirds, shorebirds, waterfowl, and other species migrate after sunset. Night travel helps them avoid daytime predators, high temperatures, and some forms of turbulence. Cooler air also reduces the energy required for sustained flight.

Birds rely on several environmental signals during migration. These include the Earth’s magnetic field, coastal outlines, wind patterns, and the position of celestial bodies. Artificial light can interfere with these signals, particularly during cloudy, foggy, or overcast conditions. A bright building may become more visible than the night sky, drawing birds toward an unsafe area.

Young birds may be especially vulnerable because they are completing their first major migration. Their behavior is partly inherited, but experience also shapes their decisions. Artificial light can interrupt the development of normal travel patterns.

How Artificial Light Affects Migratory Birds

Light pollution harms birds in several related ways.

First, it can cause disorientation. Birds that encounter bright light may circle a source repeatedly rather than continue along their route. This behavior consumes energy that the birds need for migration, feeding, and reproduction.

Second, birds may become trapped in illuminated areas. They can remain near a building until daylight, when they face additional risks from traffic, predators, and human activity. Exhaustion can reduce their ability to resume flight.

Third, artificial light increases collisions. Birds often see reflected trees or sky in glass but do not recognize the surface as a solid barrier. Light from inside a building can make windows more attractive or obscure their reflection. During migration, a single structure may kill or injure large numbers of birds.

Fourth, nighttime lighting can alter sleep, feeding, and hormone cycles. Birds use changing day length as a seasonal signal. Excess light may affect the timing of migration, breeding, and rest. It can also change insect behavior, reducing or shifting access to food.

The Link Between Light and Glass Collisions

Lighted buildings are dangerous partly because they create a visual trap. A bird flying through the night sees a bright interior, a reflected tree, or an apparent opening. It may strike the glass at full speed.

The risk is not limited to skyscrapers. Low-rise offices, homes, schools, and apartment buildings can also cause collisions. Large windows near vegetation are particularly hazardous because birds see leaves and branches in the glass and attempt to reach them.

Window treatments can reduce this danger. Exterior screens, awnings, shutters, and closely spaced markers work better than a few decals placed far apart. Interior blinds and curtains help at night, especially when lights are turned off. Bird-safe window film can also reduce reflections and make glass more visible.

Simple Ways to Help at Home

Small household decisions can reduce harm without making homes unsafe or uncomfortable.

• Turn off outdoor lights that are not needed.
• Use motion sensors or timers instead of leaving lights on all night.
• Aim fixtures downward and shield the sides so light stays near the ground.
• Choose the lowest brightness that serves the intended purpose.
• Close curtains or blinds after dark, especially during spring and fall migration.
• Place indoor plants away from windows so their reflections do not create false habitat.
• Add exterior screens or closely spaced window markers to collision-prone glass.
• Keep porch and landscape lighting off during peak migration periods when practical.
• Avoid blue-rich, high-color-temperature bulbs outdoors. Warmer light is generally less disruptive than harsh white or blue light.

A dark porch does not need to be completely unlit under every circumstance. Safety should guide lighting choices. The goal is to use light only where it is needed, for as long as it is needed, and at an intensity that serves a clear purpose.

For another practical way to support backyard birds, see the safest place to put a bird feeder in your yard.

What Communities and Businesses Can Do

Cities, building owners, schools, and property managers can reduce bird deaths through coordinated action. During spring and fall migration, they can turn off decorative and nonessential lighting during the late-night and early-morning hours. Some communities establish seasonal programs that encourage businesses to darken upper floors, lobbies, and unused offices.

Architectural design also matters. New buildings can use fritted or patterned glass, exterior shades, screens, and other materials that make windows visible to birds. Existing buildings can add films, screens, or patterned treatments without replacing every window.

Outdoor lighting ordinances can limit glare, upward-directed light, and excessive brightness. These rules benefit people as well as wildlife by reducing energy use, preserving views of the night sky, and limiting glare for drivers and pedestrians.

Building managers can also record bird strikes and rescue injured birds through local wildlife rehabilitation groups. Consistent records help identify dangerous structures and direct improvements to the places with the greatest need.

Why Darker Nights Benefit People

Reducing artificial light has practical benefits beyond bird protection. Excessive nighttime lighting can disturb human sleep, create glare, obscure stars, and waste electricity. Bright, poorly aimed fixtures may make it harder to see rather than easier by producing sharp contrasts and reflected glare.

Well-designed lighting uses a smaller amount of light more effectively. Shielded fixtures reduce light that enters windows or shines into neighboring properties. Timers and motion sensors lower energy use while preserving lighting for necessary activities.

FAQs

Which birds are most affected by light pollution?

Night-migrating songbirds are among the most frequently affected, but shorebirds, waterfowl, rails, thrushes, warblers, and other species can also become disoriented. Any bird that travels through an illuminated area may face added risks.

Are all outdoor lights harmful?

No. The risk depends on brightness, color, direction, timing, and location. A low-intensity, warm-colored light aimed downward is generally less disruptive than a bright fixture that shines upward or across a large area.

Do window decals prevent bird collisions?

They can help when applied across the glass at close intervals. A few decals separated by large spaces may not provide enough visual information for birds. Exterior screens and dense patterns are often more effective.

When should people reduce outdoor lighting?

Spring and fall migration are the main periods of concern. Exact timing varies by region, but reducing unnecessary lighting throughout the night is helpful whenever migratory birds are passing through.

What should I do if I find an injured bird?

Gently place the bird in a small box with air holes and a soft cloth on the bottom. Keep the box dark, quiet, and away from pets. Do not give the bird food or water. Contact a licensed wildlife rehabilitator as soon as possible.

Can one household make a difference?

Yes. A single darkened home prevents less harm than a coordinated citywide effort, but household action supports broader changes. Turning off unused lights, treating hazardous windows, and encouraging neighbors or building managers to participate are practical steps with measurable value.