The 'Brilliant Toad' Was Telling Us Something

How does it feel to be the first scientist to discover and describe a truly extraordinary species, only to have it become extinct 25 years later?

In Monteverde, Costa Rica, one night in 1963, I struggled along with two companions up a narrow muddy trail to a fog-shrouded but wind-swept ridge. Under the dark and stunted trees, hundreds of bright orange-to-gold flashes of color vividly contrasted with the leaf-littered forest floor. Each flash turned out to be an adult male golden toad. On closer inspection we discovered females of this species, which unlike the males were olive to black, with large scarlet spots.

It turned out that the golden toad - which I named Bufo periglenes (brilliant toad) - lived only along a few ridges near Monteverde. There it remained in hiding for most of the year, emerging for a few short weeks to form a breeding congregation of hundreds.

In the years since, the residents of Monteverde established a totally protected forest reserve to preserve the habitat of the golden toad. Each spring for 24 years, large numbers of the toads made their brief, frenetic appearance.

Then in 1988, only a few toads were seen, in spite of extensive searches. In 1989, only one lone male was known to have been encountered by anyone. Since then, a continued search involving a monthly monitoring program by residents and researchers has turned up no golden toads.

The species is presumed extinct.

What a terrible feeling to realize that within my own lifetime, a species of such unusual beauty, one that I had discovered, should disappear from our planet.

Sad though it is, there's more to the story than the demise of a single species.

More or less simultaneously at Monteverde and other pristine sites throughout the world, many other kinds of frogs, toads, and some salamanders showed spectacular population crashes, leading in some cases to other apparent extinctions.

Generally, the declines began in 1988, with no sign of a rebound since then.

By the 1990s a number of scientists had become increasingly concerned by the apparent pervasiveness of the declining amphibian populations (DAP) phenomenon.

The concern was heightened by the fact that DAP - occurring quietly but rapidly in far-flung corners of the world - could be signaling something amiss on a broader scale.

Could DAP represent an early-warning system of a coming major environmental change?

Amphibians are particularly sensitive to environmental disturbance. They have permeable skin and, in their biphasic life, spend their larval development in the water and their adult stages on land. So they may be affected by environmental deterioration well in advance of other organisms.

Early on, some biologists tried to attribute DAP to natural fluctuations in population size, primarily because long-term data were not available for many affected species. Recent detailed studies in Australia, Costa Rica, and Panama have conclusively dem-onstrated the reality of the amphibian disappearance. In these cases, both the magnitude and extent of the declines in undisturbed sites exceed any expectation that DAP is the result of natural population fluctuations.

Now that the reality of DAP is established, scientists have turned to evaluating possible causes.

The similarities of the pattern of declines in lower Central America and Australia have led researchers in both areas to postulate that the cause of the declines was an epidemic. The cause of frog deaths in both widely separated regions of the earth is believed to be the same fungus.

This discovery came about when biologists in the field noticed many dead and dying frogs at previously unaffected sites, followed next year by spectacular population crashes.

The ultimate cause of this is another question.

My research team has gathered evidence that cumulative climate change - even slight global warming - seems to increase the number and frequency of drought periods in a given year. These may so stress amphibians that they become susceptible to disease.

There is a strong correlation between the increased frequency and severity of El Nio events, beginning in the late 1970s, and the onset of amphibian declines. This progression, in turn, is linked to the continuing and unidirectional buildup of greenhouse gases added to the earth's atmosphere by human activity.

Unless this trend is stabilized, it seems that not only frogs but the health of the global environment will remain at risk.

* Jay M. Savage is professor of biology at the University of Miami.