It's likely that the only time you really notice one of your neighborhood broadcast and cell towers is at night when they're lit up with conspicuous bright red lights.
Those lights help pilots see the huge metal structures that can reach 1,000 feet into the air — but they can spell disaster for birds.
In 1976 in Gun Lake, Mich., one tower killed more than 2,300 birds in one night, says Caleb Putnam, who has a joint position with the Michigan Department of Natural Resources and Audubon Great Lakes. He says for reasons scientists still can't quite figure out, birds kept flying headlong into towers.
"If that many are dying in one night at one tower and yet there are thousands of towers across the country and as you go across the world, the numbers are staggering," he says.
Putnam says in North America alone it's estimated that 7 million birds smash into towers every year. But until recently, scientists didn't know why it was happening.
Figuring that out became biologist Joelle Gehring's mission. She helped conduct a study in 2003 to find out what could be done.
Gehring, standing recently at a broadcast tower in rural northeast Michigan that belongs to the local radio station, says every morning in the spring or fall — the peak migration season — she and others had the unpleasant job of counting dead birds at the base of these towers.
What she discovered was surprising.
"We were able to reduce the numbers of bird fatalities on communications towers by simply extinguishing those nonflashing lights," she says. "Those fatalities were reduced by as much as 70 percent."
Exactly why isn't yet clear, but she has a theory.
"Some research has documented that when birds are exposed to long wavelengths of light such as red or white that it actually interferes with their ability to use magnetic fields for navigation," Gehring says.
She says that's especially true on cloudy nights when birds can't navigate by the stars. The towers' steady red lights seem to confuse them. Flashing red lights don't.
In 2015, the Federal Aviation Administration changed regulations on new towers, requiring that they all be built with only flashing lights.
Gehring, who now works for the Federal Communications Commission, spends much of her time contacting people who run towers built before 2015 and encouraging them to switch to blinking lights.
"And when we drive back and forth around those beautiful Great Lakes at night, we see more and more communications towers that are lit with only flashing lights at night, and my son always points out 'another bird-friendly tower, Mom,' " she says.
There are still tens of thousands of towers though that aren't bird-friendly, as birds are drawn to the solid red lights. Gehring and others will continue to try to save those birds by doing one simple thing: changing those tower lights.