From TOWERING TROUBLES:
“…Our TV and cell phone habits are contributing to the deaths of millions of migratory birds a year. The birds collide with the communications towers …and with the cables that anchor the towers. Those towers become sky-high death traps for birds, who then drop in grass, streets, parks, and fields, and on rooftops….conservation groups and government biologists estimate that communications towers kill from 4 to 50 million birds a year. They endanger or threaten at least 50 species….
…The construction of new towers is deadly news for migratory birds. The tower-bird collisions occur (1) during spring and fall migrations, and (2) at night, when songbirds travel to avoid the heat and daytime predators. For birds, such as whooping cranes, that fly during the day but cannot see the power lines, the towers and lines are the Number One migration danger. …
…Many of these nighttime travelers can cross oceans and navigate mountain ranges. What makes them crash into the blinking, lighted towers? Scientists aren’t certain. The worst kills happen when a flock, which might number half a million, flaps toward a lighted tower. Something about the lights attracts the birds. Red beacons seem to draw birds more than other lights do, although studies suggest that red wavelengths may disrupt the birds’ ability to navigate using the stars or the earth’s magnetic fields. The weather may play a role, since large kills almost always occur on cloudy or foggy nights. Fog, mist, or storms increase the odds of trouble. Unlike larger birds, which can climb above the clouds, smaller migrants sometimes try swooping underneath, right into the path of towers. “