During the day, reflected light poses a severe threat to birds. Birds can see through glass and what is reflected on glass, but they cannot see the glass itself.
Attracted to the reflection of a landscape that is actually behind them, or to a plant that is on the other side of a window, many birds fly straight into windows and reflective building exteriors.
Some birds have even been observed attacking their own reflection, believing it to be a competing bird intruding on its territory.
At Night
At night, it is artificial light from our buildings and cityscapes that endangers birds. Many species of birds migrate at night, using light from the moon, the stars, and the setting sun to navigate. The bright lights of our urban areas confuse these birds and pull them out of their way.
Especially on foggy or rainy nights when the cloud cover is low, birds fly at lower altitudes and are more likely to be disoriented by city lights. They may be pulled down into downtown mazes, where they often collide with buildings.
Also dangerous are floodlights, lighthouses, and airport ceilometers (light beams for measuring cloud altitude). Studies using radar have shown that, once birds are attracted to a light source, they tend not to want to leave it. Birds may become trapped inside beams of light, flying around inside them until they drop from exhaustion.
To learn about how night lighting has a negative impact on humans and the environment, visit the International Dark-Sky Association.
Crashing into a building, whatever the cause, often results in death on impact. Even where a bird is not killed outright, it may fall to the ground stunned, where it is vulnerable to predators. Or the collision may cause serious injuries that the bird cannot recover from in time to continue its migratory journey.
