These may well have been the first voices heard on Earth. These chirps and squawks, these trills, barks, basso profundo croaks. These voices of frogs and toads have been constant as the wind and perhaps as full of portent.
The voices have been heard long before there were humans on the planet to notice or wonder what messages they might convey. In the last decades of this century, frogs have been speaking with an ever-expanding silence, a troubling message scientists are working to decipher.
This appears to be a precarious time in the life of a species that has lived on Earth nearly 200 million years. With frogs vanishing across the globe, it's as good a time as any to stop and listen to this primeval voice in many of its remarkable incantations. It's not all ribbitt, ribbitt, ribbitt. It's hardly that at all.
One learns this by listening to a compact disc that appears in stores this week: "Sounds of North American Frogs," being re-issued by Smithsonian Folkways Recordings 40 years after it first appeared. The $14 CD is a herpetology classic, the product of expeditions on the frontier of field recording.
"It's the starting point for the scientific study of amphibian voice," says Ronald Heyer, curator of amphibians and reptiles at the National Museum of Natural History in Washington, part of the Smithsonian Institution.
The recording, made by biologist Charles M. Bogert, was put out originally in 1958 by Folkways Records, a New York-based label acquired in 1987 by the Smithsonian Institution. Smithsonian Folkways is re-releasing the album -- one of the most popular in Folkways' "Science Series" -- to observe the 50th anniversary of Folkways and to mark a time of concern over frogs. Frogs and toads are dwindling in some parts of the world and turning up with grotesque anatomical deformities in others.
What is 40 years in the life of a species that lived alongside the dinosaurs? Enough time for scientists to turn from questions about its ways of life to wonder if they are witnessing its widespread demise.
Such dark notions did not trouble Bogert, who from 1942 to 1968 was curator, then chairman of the department of amphibians and reptiles at the American Museum of Natural History in New York City. In the 1950s, he ventured out in search of frog voices. Ornithologists at Cornell University had recorded East Coast frogs in the late 1940s for identification. Bogert considered more complex questions. Why did the frogs use these sounds? Did different sounds serve distinct purposes? How sensitive are frogs to pitch?
Bogert had help in the pursuit from a couple of postwar technological innovations. One was the sound spectrograph, which in effect draws pictures of sounds, allowing detailed analysis. The other was the portable tape recorder. Bogert lugged a Magnamite recorder, a heavy metal contraption the size of a thick briefcase, its recording element powered by batteries, its reels driven by a wind-up spring motor. He ranged across the United States, into Mexico and Central America.
Bogert, who died in 1992, narrates the recording, which features 57 species on 92 tracks. As of last year, there were 95 species of frogs identified in North America, a fraction of the world population of about 4,100 species.
The range
In a flat voice, Bogert guides us through stream, swamp, river, forest, plain and desert. Some frogs are heard in isolation in the field or in a laboratory. Others are heard as part of a great wilderness chorus of several species and hundreds of frogs and toads.
Without Bogert's guidance, without the help of the 40-page liner notes, a novice would not know these are frogs. On this recording, only the American bullfrog, the Pacific tree frog and the pig frog emit the stereotypical froggy croak.
The rest sound like any number of things. The barking tree frog might be mistaken for a heart monitor in an intensive-care unit. The green tree frog honks like a high-pitched goose, the oak toad peeps like an osprey. The squirrel tree frog imitates a duckling and the Florida gopher frog sounds like an 80-year-old man snoring. The mating call of the southwestern woodhouse toad could be a scream from the latest "Halloween" sequel. There are frogs that sound like rattlesnakes, crickets, Yorkshire terriers, chattering birds, rubber bands snapping.
The purpose of the calls varies from one species to another. Frogs may use sound to find mates, warn an aggressor, establish territory. On one of his nighttime expeditions in Florida, Bogert heard behind him an awful scream. He wheeled around with his flashlight and saw that the sound came from a southern leopard frog, terrified, clasped in the jaws of a raccoon.
Today, scientists around the world are working to understand a silent cry of frog distress.
In Australia and Central America, in parts of South America, the United States and Canada, even in areas far from where people live or work, frog populations have been declining since the late 1970s, a phenomenon established by observation but not specific frog counts. Two species have not been seen since the 1980s and are considered extinct: the Costa Rican golden toad and the Australian midwife toad, says Sam Droege, a biologist with the U.S. Geological Survey at the Patuxent Wildlife Research Center in Maryland.
In Minnesota and other states, frogs have been found with severe deformities: missing limbs or eyes or having an extra pair of hind legs.
In Maryland, sharp declines have been noticed among four of the 20 species that inhabit the state, says Don Z. Forester, herpetology specialist at Towson University who has conducted annual surveys for 25 years. In three cases the frogs have dwindled as their habitat has been destroyed by development. But that doesn't explain the precipitous decline of the upland chorus frog, which lives on the western shore in remote areas -- to the extent that there are any remote areas in Maryland.
"It's really declined," says Forester, "for reasons that are totally unclear."
Scientists have reached a consensus on the seriousness of the global problem, says Heyer, who chairs the Declining Amphibians Populations Task Force, an alliance of about 1,000 volunteer scientists operating under the auspices of the World Conservation Union. Even those who were skeptical in the early 1990s have come to recognize a cause for alarm.
'Environmental indicators'
So far, theories outnumber explanations. Increased ultraviolet radiation resulting from ozone depletion is one suspect. So are pesticides, global climate change and diseases, including a water fungus not previously believed to affect vertebrates.
Studies of frog deformities have pointed to the insecticide methoprene, which can break down chemically when exposed to water and sunlight and mimic a hormone that causes birth defects.
Gary Fellers, biologist with the U.S. Geological Survey in Point Reyes, Calif., says he also suspects that pesticides have thinned frog populations in remote areas of the Sierra Nevada Mountains. Because frog declines have occurred on the western slopes facing the agricultural Central Valley, Fellers believes airborne pesticides are drifting into the mountains and killing frogs.
"The implications certainly go beyond amphibians," says Heyer. "They probably are very good environmental indicators. What is knocking them off is probably affecting us as well and we don't know it yet."
It's something to consider while listening to "Sounds of North American Frogs." All these strange voices saying something. And the silence when the recording ends, implying something else.
Pub Date: 8/06/98