An aspect of migration that has come under increasing scrutiny is the flight call given by each species. Combined with radar study, it can help determine the identity and density of birds passing over a particular location late at night. Now some birders are finding ways to study the phenomenon of nocturnal flight calls themselves.
I took a look at the oldbird site myself. The microphone rig looks a bit like something off the Red Green Show (complete with duct tape and bungee cords), but presumably works.
A high-powered microphone can be set up at home, even in the city.
"Cities are often best, because there are a lot of lights, and they're near the coast," Dr. Wells said. Birds can get confused by bright lights, which makes them call to each other more frequently.
At the Web site www.oldbird.org, instructions show how to build a microphone on a plastic-wrapped dinner plate, kept inside a flower pot, for about $10 (look toward the bottom of the listing on microphone design). It also offers free software that sifts through the various calls overnight, producing spectrograms and keys to identifying what bird produced them.
"I warn any of you to be careful: You won't sleep at night," Dr. Wells said. "And in the morning, you'll have to run right to your computer to find out what went over your house all night."