From the NJ Audubon Society:
“‘An estimated 5,000 to 10,000 birds, mostly Lapland Longspurs, were killed on the night of January 22, 1998, at a 420 foot tall communications tower in western Kansas. Apparently a heavy snowstorm sent the birds up looking for bare ground. Dense fog caused the tower’s aviation-safety lights (required on structures over 200′) to reflect off water in the air and form an illuminated space, causing the birds to switch to their diurnal (visual) mode of navigation. The flock circled the lighted tower and collided with its guy wires. Some birds were impaled by wheat stubble, suggesting they were so disoriented that they couldn’t tell which way was up and flew into the ground at full force. The tower had three white strobes. This is interesting because it has been suggested that flashing lights cause less mortality than steadily illuminated lights. Evidence suggests that continent-wide, communications towers kill 2 to 4 million songbirds each year.’ (American Bird Conservancy, Bird Calls, March 1998).
…five tower kill studies done in the eastern US in recent decades all showed kills of roughly 1,000-3,000 kills per year….
The problem is caused by the lights on the towers for aviation warning. On nights with a low ceiling, birds lose their cues for stellar and geomagnetic navigation. The light reflecting off water molecules in the air causes an illumined area, creating a whirlpool of birds circling the tower in the light space…
Some of these documented cases of tower kills are very revealing. Many of them indicate a very high percent of forest Neotropical long-distance migrants, especially warblers.”
The full, longer article on this, is at the link above.