Tracking the Vanishing Frogs: An Ecological Mystery.

When my wife recalls the summers of her childhood, in a village in the South Korean countryside, she can still hear the nightly, ear-numbing racket produced by the frogs in the rice paddies. The croaking was so loud and so constant that people labored not to pay attention to it, for the sake of their sanity. Today, the frogs no longer sing in South Korea's paddies. To many middle-aged Koreans, their silence is a mournful thing--a mute reproach for a 30-year pesticide binge.

There may be other parts of the world where the frogs sing only in the memories of the middle-aged. Certainly there are many places where the paddies, ponds, and forests have fallen silent more recently. By 1990, a growing number of biologists had begun to suspect that these thousand little tragedies were parts of a single, much larger drama--and one that seemed to be unfolding with menacing speed. This is the story that Kathryn Phillips sets out to tell in Tracking the Vanishing Frogs. A science journalist, Phillips spent nearly three years following biologists around in the field as they looked for frogs, toads, and salamanders. She read their papers and attended their conferences. And she spent hours interviewing them, along with amateur frog breeders, U.S. Fish and Wildlife Service officials, and other people whose lives, for various reasons, are full of amphibians.

The class Amphibia includes frogs, newts, salamanders, toads, and a group of worm-like subterranean creatures called caecilians. Amphibians are among the oldest terrestrial vertebrates. The first members of the class appeared some 365 million years ago. Those creatures bore no close relation to modern amphibians, but frogs emerged perhaps 200 million years ago. Frogs must have serenaded the dinosaurs and hopped away at their foot fall. Today, there are about 4,500 amphibian species, distributed throughout the globe, except in the polar and desert regions. Every year, a few new species are added to the rolls.

It's difficult to understand what is happening to amphibians because for most species, we aren't sure where they are supposed to be and how many of them should be there. There is some evidence, for instance, that wild fluctuations in population size may be normal for some species, so a sudden scarcity might just indicate a bad but perfectly "natural" year. And there are many populations that are doing very well. The evidence for global decline is therefore a matter of anecdote. But the anecdotes are overwhelming: 10 percent of Australia's frog species went into decline during the 1980s; Brazil's Reserva Atlantica has lost eight of its 13 frog species since 1981; amphibian die offs have been reported in Denmark, Peru, India, Canada, the United States, and at least 11 other countries.

That an entire class of animals--and one as durable as Amphibia--should suddenly go into decline is ominous to say the least. Some biologists argue that certain amphibian characteristics make the story even graver. Amphibians have very permeable skin, which renders them especially susceptible to toxins. Their life cycles are generally divided between land and water, making them very vulnerable to habitat disruption. These vulnerabilities may qualify amphibians as bioindicators: their health may be a good test of the health of an ecosystem. In this respect, amphibians may resemble birds, another class of animals suffering a broad decline (see "Flying into Trouble," [January/February 1994]).

Phillips explains these issues by taking us into the field, where we meet both the biologists and their quarry. Martha Crump, for instance, is an ecologist at the University of Florida. In 1987, she travels to the Monteverde Cloud Forest Preserve in Costa Rica to study tree-frog tadpoles. But her April visit happens to coincide with a mating emergence of one of the most beautiful amphibians in the world: the golden toad (Bufo periglenes). The males of the species, under two inches long, are a brilliant, glowing orange-gold. Even in pictures--and there is a set of color plates in the book--they look almost supernatural, as if they belong in the realms of Mayan myth. The females look completely different: they're larger and nearly black, with red spots ringed in yellow.

In the middle of the night, squatting in a cold and heavy rain, Crump watches hundreds of males congregate in pools "among the ferns and heliconia," waiting for their mates to appear. "They've been described as little jewels on the forest floor, and that's really the impression you get," she says. The next year she returns, but months of observation yield only ten toads. The year after that she spots only one. Later in 1989, Crump attends the First World Congress of Herpetology in Canterbury, England, where she mentions the phantom toads to her colleagues. Many have similar disappearances to report. For the first time, these private anxieties coalesce into an hypothesis of global proportions.

Phillips devotes a couple of chapters to Mark Jennings and Marc Hayes, two biologists who are surveying all of the native amphibians in the state of California. With an area of more than 41 million hectares (158,706 square miles), and terrain varying from coastal rainforest to desert to alpine meadow, California is a generous sample of the planet: understanding the state's amphibians should provide for more solid inferences elsewhere. Jennings and Hayes live off teaching, consulting, and short-term grants, but they live for their grueling field expeditions. Phillips gives us a clear sense of how this sort of work is done. We watch the pair stalking frogs in the marshes, dissecting specimens, and writing up notes. We also learn the results of their survey. California has about 47 native amphibians -- the total varies somewhat because the taxonomy is not settled. Of these, 32 may be in trouble.

One of Phillips' objectives is to produce a chronicle of contemporary science as intellectual event. This is apparent from her subtitle, "An Ecological Mystery." She wants us to know what it was like for Crump and her colleagues to piece together a global problem from many local ones. The labor of discovery figures elsewhere too. Alan Pounds, a former graduate student of Crump's, convinces Crump that weather and hydrological data can be combined to reveal a "drought" at Monteverde even in years when Crump was a soggy witness to what seemed like plenty of rain. The two collaborate on a paper suggesting that unusual weather was a factor in the reserve's amphibian declines. Phillips also describes the experiments that lead another team of researchers to conclude that some frog species can sense destructive ultraviolet light and will actively avoid it.

If the inner life of science is a subject of growing interest, that may be due to the success of James Gleick's Chaos: Making a New Science, published in 1987. Gleick described the mental exertions of climatologists, physicists, mathematicians, and ecologists to find a kind of order in the random--a dimension now known, rather enigmatically, as the complex. Gleick built his story out of the most abstruse forms of analysis, but Phillips' ecologists have more tangible problems to face. This might be poorer fare as a purely intellectual exercise, but at critical moments in her story, Phillips succeeds in conveying the sour-stomach urgency of the questions her scientists pose. Are Crump's ethereal golden toads, which seemed so plentiful only a few years before, really all gone? (Apparently, they are.) And what happened to Australia's incredible gastric-brooding frog (Rheobatrachus silus)? In 1973, Michael Tyler, a biologist at the University of Adelaide, discovered that this creature raises its young, from eggs through tadpoles to froglets, in its stomach and then vomits them forth. The frog's reproductive strategy is so bizarre that Tyler's paper on it was rejected by the journal Nature because the editors thought it was a hoax. With no known parallel in nature, with clear medical applications, the gastric brooder is in demand. But it hasn't been seen since 1979.

There is also recent precedent for field biology as narrative. In 1990, Don Stap's A Parrot Without a Name turned a Peruvian birding expedition into literature. The biologists in Stap's account, like those in Phillips', are motivated by a sense of urgency: they too fear that time may be running out for their subjects. But Stap himself takes the time to evoke a sense of place. We see the grubby backwater towns and the amazing forests in far greater detail than the plot itself appears to demand, and that gives the narrative a generous, almost epic quality. Stap, however, is a published poet. Perhaps because of her years of journalism, Phillips usually shows us only those features of the scene that are necessary to move her argument.

But Phillips knows how to deploy her plain style to devastating effect. One of her subjects is Sam Sweet, an eccentric, chain-smoking herpetologist at the University of California at Santa Barbara. Sweet eats cold cheeseburgers, carries a gun, and has vowed to force-feed a soiled Pamper to the first camper he actually sees tossing one into a stream. He is the champion of the arroyo toad, a rare inhabitant of southern California's upland forest streams. Sweet feuds with the U.S. Forest Service, which insists on rebuilding a washed-out road solely for the benefit of a private rancher, despite the fact that the roading will destroy prime arroyo toad habitat. In Phillips' careful, matter-of-fact account of these events, readers may recognize their own encounters with natural resource management by bulldozer. Or, as Phillips puts it, "The toads have probably occupied this part of California for twelve thousand years, surviving ice ages, fires, and floods galore. Now their biggest test is to survive the Forest Service."

One serious limitation of Phillips' account is that she focuses almost exclusively on the United States and Costa Rica. Apart from a few examples, there is little discussion of amphibians in other parts of the world. This bias is due partly to the nature of the research: these areas are among the best studied. Little is known about the amphibians of Africa and much of Asia. South America, too, is still largely a mystery, but I gather that some work has been done on Brazilian amphibians. Western Europe's amphibians have also been the subject of study. Phillips might have broadened her account by including more of these.

While her focus may be narrower than one might have hoped, Phillips compensates by including several major asides to her main theme. For instance, we learn something of the history of amphibian gastronomy, especially in California. The California redlegged frog (Rana aurora draytoni), became a game animal when a fad for French cuisine swept California towards the end of the last century. That accounts in part for its rarity today. As for the French themselves, once populations of their own Rana esculenta were exhausted, they turned to central European and Turkish frogs. Today, the largely western appetite for frog legs has drained populations ever farther east, first in India and Bangladesh, now in Indonesia.

We also meet some frog hobbyists--collectors and amateur breeders who seem to have built their lives around the demands of their charges. One of them has constructed a kind of frog terrarium the size of a three-car garage. Collecting for the pet trade may add to the pressure on some wild populations, and captive breeding may have a role in restoring some. Asides like these have an obvious relevance to Phillips' main story, but they also help her develop a broader theme. Most of us probably devote little thought to toads and frogs, but people and amphibians do have a relationship that is complex enough to merit a history.

In her later chapters, Phillips focuses less on field work and more on possible explanations for the declines observed. Many problems, of course, are no mystery: grazing, logging, and development are destroying huge swaths of amphibian habitat. Introduced sport fish prey on frog eggs and tadpoles. Pesticides continue to take a serious toll. But there appear to be broader factors at work as well: acid rain, the thinning of the ozone layer, and climate change have all been invoked as possible causes for declines, especially in areas where there has been little obvious disturbance of habitat. Phillips' workmanlike review of these topics assumes little prior knowledge.

More insidious than any single factor is the possibility of a synergistic effect, in which several apparently minor stresses combine with devastating force. Phillips uses the work of Crump and Pound to explore this possibility. They hypothesize that the golden toads may have disappeared because a change in water regime coincided either with an attack of parasites, a disease, or with pesticide contamination of atmospheric moisture.

One important idea implicit in Phillips' account but not addressed directly is the principle of the metapopulation. Little localized extinctions may be relatively common in some amphibian habitats, yet the species involved aren't necessarily endangered because vacant habitat can be replenished from nearby populations. Collectively, all these little fluctuating populations make up one large and relatively stable metapopulation. But the mechanism only works if amphibians can get from one constituent population to another. If you stock a couple of streams with introduced fish, or build a few roads, you may break the links and the whole system could collapse.

As Phillips shows, none of these explanations yields an entirely satisfactory explanation for amphibian decline. One of the few points of scientific consensus seems to be that there is no single factor at work. Biologists still have no idea how many species are in decline, or what the declines tell us about the fate of the ecosystems in which they live. But if Phillips has not solved her ecological mystery, it's hard to imagine that her readers will have any doubts about its importance.

Chris Bright is Associate Editor of World Watch, and a former Assistant Editor of American Horticulturist.