ECOVIEWS
FUN WITH A FROGLOGGER
Technology and the environment. The positive, such as air conditioning, cars, hydro-electric plants can also be negative: ozone depletion, smog, dammed rivers. But for technology with two positives, try frogloggers and the discovery of rare frogs.
A froglogger is an automated recording system, a tape recorder designed to start and stop automatically when no one is around to operate it. Many birds, insects, frogs, and mammals communicate by sound. So a well-placed recording system can keep track of numerous forest sounds when no one is there.
Some technology that seems simple is taken for granted after all the bugs have been worked out and someone shows us which buttons to push. Such appears to be the case with the froglogger after work by Charles Peterson of Idaho State University and Michael Dorcas of the Savannah River Ecology Laboratory. They tinkered and toyed with automated recording systems for purposes of detecting frog calls. The product is a recording device housed in a weather-resistant box and programmed to record for intervals from a few seconds up to a minute or more each hour.
An internal clock, audible to the listener, announces the time when each recording begins so that ecologists can know when certain sounds were made. A solar panel keeps the battery charged, and the recorder can go for a week or more before tapes need to be changed. Then begins the real fun with a froglogger. The tapes must be listened to and the sounds identified.
At a recent froglogger "party," six of us sat in my living room listening to the stereo play sounds of the night. The froglogger, programmed to record for a one-minute interval each hour from dusk till dawn, had been placed alongside a natural wetland at the Savannah River Site in South Carolina. Calling frogs can be detected in this way because frog choruses often take place over a period of several hours. With the froglogger tapes, we were able to compress two full weeks of nighttime frog calls into a three-hour session.
We settled back to listen. Night in the forest away from city sounds is full of music, and we recognized most of the songs we heard. The rapid chuckling of leopard frogs and the clicking of cricket frogs were heard on every night. On cool nights we heard the cheeps of spring peepers, on warmer ones the banjo-like strums of bronze frogs. We also recognized a distant, mournful train whistle. Two barred owls challenged each other with their "who cooks for you all?" hoots. The next day we confirmed that the distinct crash we heard during a windy night was that of a dead pine tree that had stood near the froglogger station.
We may never know the identity of other sounds on the tape. Did we really hear a coyote howling? Was the large animal splashing through shallow water at the edge of the wetland a deer, wild pig, alligator? But the most significant sound, and one we could all identify, was not unlike an old man snoring--the mating call of the gopher frog, one of the rarest amphibians in the eastern United States.
The call was recorded on two tape segments during a rainy night. Gopher frogs are so rare they are known to be in only a handful of locations in South Carolina. In some years during the last two decades none has been seen or heard anywhere in the state for the entire year. The froglogger had confirmed the gopher frog's occurrence at a wetland where it was formerly unknown.
Frogloggers are destined to become a major environmental sampling tool. To elevate the technology further, Mike Dorcas is working with Ontario Hydro Technologies, a company developing computer software to identify frog calls. For example, a tape from a froglogger can be digitized into a computer sound file. The file can then be played into the software program for the computer to identify the calling species of frogs. The software can also eliminate sounds, such as passing trains or traffic, that might make it more difficult to hear frogs calling. The more rapid interpretation of sound tapes will result in a technology that will be of enormous value in environmental assessments of vocal animals.
If nothing else, the froglogger has answered one question that has nagged people for centuries. A tree falling in the woods does make a sound, whether anyone is there to hear it or not.
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