Nighttime Migration: Protecting Birds This September

Each fall, billions of birds journey south to their wintering grounds. September is one of the busiest times for migration across North America, as warblers, thrushes, sparrows, and other songbirds stream overhead. While the cover of night helps protect these travelers from predators and overheating, it also introduces new dangers. Artificial lights and reflective glass disorient birds, leading to tragic collisions. By understanding how and when birds migrate, we can take action to make their journey safer.

Why Birds Migrate at Night

• Cooler air: Nighttime temperatures allow birds to conserve energy and avoid overheating during long flights.
• Calmer winds: Air is often more stable at night, reducing the physical strain of migration.
• Fewer predators: Darkness helps birds avoid hawks and other daytime threats.
• Celestial navigation: Many species use stars, the moon, and Earth’s magnetic field to find their way south.

This strategy is effective, but it leaves birds vulnerable to human-made obstacles. Bright city lights and illuminated homes can draw birds off course, and glass becomes especially deadly when disoriented birds land in unfamiliar areas.

Spot the Difference: Dusk vs. Late Evening

At dusk, only a few early migrants take to the skies. By 10:30 p.m., migration is often at its peak—radar studies show the number of birds aloft surges late in the evening, frequently peaking around midnight. That’s why “Lights Out” efforts are so critical: turning off unnecessary lights can prevent mass disorientation when the skies are busiest.

Reducing disorientation will help reduce the number of birds that end up in bult-up environments during the day thus reducing the likelihood of daytime fata collisions. 

What Happens at Dawn: The Window Collision Problem

Although most birds fly at night, they land at dawn to rest and refuel. That's when they encounter our homes, offices, and neighborhoods. Tired and stressed from long flights, they’re more likely to strike reflective glass during the day.

While they may become disoriented at night, the majority of reflective-glass collisions occur after dawn when birds are active near windows.

That’s where WindowAlert products come in. UV-reflective decals break up reflections and make glass visible to birds, reducing collisions when migrants are most vulnerable. Lights out at night + decals by day is a powerful one-two punch to keep birds safe.

Bird Spotlight: Swainson’s Thrush

The Swainson’s Thrush is one of migration’s most remarkable travelers. Modest in appearance but stunning in voice, these thrushes migrate from forests across North America all the way to South America each fall. Their flute-like calls spiral downward and can often be heard on September nights as they pass overhead. Though shy and elusive in daylight, they rely on safe stopover habitats. So on a cool September evening, step outside and listen for their call.

September is a season of awe as billions of birds make their way south under the cover of darkness. But it’s also a season of risk, with glass collisions among the leading causes of bird mortality. By turning off lights at night and ensuring your windows are bird-safe during the day, you can help Swainson’s Thrush and countless other species complete their journey safely.