 |
|
|
Night Sounds
Tracking the nighttime movements of migrating birds
From his vantage point on a bluff above the St. Croix River, he could hear the calls of songbirds passing high above him. He recognized that one of the species he was hearing was probably a Black-billed Cuckoo--not a particularly rare bird, but one that was secretive and hard to find during the day. Fascinated, Evans began counting the birds he heard. In a little over an hour he tallied more than 100 cuckoos. Suddenly the full potential of the phenomenon he was observing became apparent to Evans. What if tape recorders were set up at strategic migration points all over the country? Researchers could listen to the tapes and identify the species and number of birds passing over each place. Most of our songbirds migrate at night and many vocalize as they migrate. Some of these species are difficult to census because they breed in the vast Canadian woodlands, where there are few roads. Recording night calls would enable scientists to study migration more accurately and monitor bird numbers over time to detect population declines. "Hearing all those birds go over was a phenomenal experience," says Evans. "At that moment, I saw the rest of my life unfold before me. I envisioned the idea of recording these nocturnal flight calls and using them to document bird populations for conservation." Evans went to an audio-visual store the next morning to look for recording equipment. He had no recording experience whatsoever, just a vivid concept of what he hoped to accomplish. The first problem he encountered was the short recording duration of reel-to-reel and cassette tape recorders--most of them record for less than two hours. "I wanted to record the whole night," says Evans. The store owner suggested that Evans buy a hi-fi video cassette recorder (VCR) and record on the sound track. "That worked out well," says Evans. "I got great sound quality and as many as nine hours of continuous sound recording on one videotape." Until recently, Bill Evans has been a one-man, self-financed research project. He single-handedly set up seven migration monitoring stations in New York State, buying all the equipment, finding volunteers to run the recorders, and listening to and analyzing every recording himself. He also traveled to other states, such as Texas, Florida, and Alabama, to record migrating birds. After nine years of independent study, his work is finally being recognized. Evans is currently a research associate at the Lab, working with the Bioacoustics Research Program (BRP) to develop software that will automatically count birds on tape recordings, and with Bird Population Studies (BPS) to help put this technology to work in the important field of migration monitoring. "I'm providing the information on the calls, and the computer wizards at BRP are using their technical expertise to develop the software program," says Evans. According to Evans, this technique of counting nighttime migrating birds could become fully automated. He envisions a time when you could check a computer printout each morning and find a listing of the quantity and identity of calling birds that had flown over your microphone the night before. "We could eventually eliminate the tape recorder and use microphones connected directly to telephone lines," says Evans. "We could set up hundreds of microphone stations transmitting bird calls to a central station. I know this sounds kind of Jules Verneish, but I can't see a reason why this could not be done in the not-too-distant future." How do ornithologists view the potential of Evans's night recording technique? According to Ken Rosenberg, chief scientist of the Lab's Bird Population Studies program, it may well revolutionize the way people study bird migration. "Almost every other way we look at migrants and try to monitor their populations involves trapping the birds or seeing them on the ground," says Rosenberg. "In some ways, we're observing the dregs of migration. We get so excited when there's a storm that causes a warbler fallout, but these events are actually bad for the birds. These birds want to go as far as they can as quickly as possible. |
