The golden toads of the Monteverde Cloud Forest Preserve, a rain forest in the mountains of Costa Rica, were numerous and easy to find as recently as 1987. The yellow-orange males and the brownish females would be seen during breeding season after they emerged from their burrows. In 1988, however, scientists reported a huge drop in the number of these toads--they saw only 10 of them. The next year, they could find only one. In December 1997, after no golden toads had been seen for several years, biologists said that the species was almost certainly extinct. Moreover, they said, the toad's disappearance could not be attributed to natural causes. Although animal numbers fluctuate naturally from year to year, the golden toad's precipitous decline led biologists to suspect that human activities were involved. Whatever the cause of its disappearance, the golden toad was not the only amphibian species in the Monteverde preserve to be affected. Six other species of frogs or toads in the forest also declined in numbers during the same period.
The frogs and toads of the Monteverde rain forest, like other amphibians, are characterized by a life cycle that is partially terrestrial (on land) and partially aquatic (in water). A typical amphibian lives on the land until it is time to breed and lay eggs, when it returns to the water. Eggs hatch into aquatic larvae (immature organisms), which live in the water until undergoing metamorphosis (changing into adults). Not all amphibians, however, go through this cycle. Many species live entirely on land or in water. Amphibians are also characterized by a lack of protective body covering, such as scales, feathers, or fur. The skin of amphibians is exposed and easily penetrated by substances in the water and air, allowing them to breathe through their skin as well as with their lungs.
Scientists have been reporting since the late 1980's that certain populations (regional groups within a species) of amphibians are in decline. And in the mid-1990's, there was another worrisome development. Many people began seeing amphibians with various kinds of malformations, including extra limbs and abnormal sex organs. Scientists are concerned about these problems because amphibians are thought to be good indicators of environmental health. The ability of amphibians to readily absorb substances from the water and air makes them more sensitive than most other animals to environmental conditions. Amphibians may thus be providing an early warning of a deteriorating environment. If so, researchers caution, whatever is harming amphibians might also pose a threat to human health.
Some biologists, however, see little cause for concern. They contend that many amphibian population declines are just natural fluctuations. Some scientists also question whether malformations are truly on the rise among amphibians. They note that deformities in frogs had been reported as far back as the 1800's.
Researchers were engaged in many studies in the 1990's to learn what--if anything--was happening to amphibians. By 1998, these studies had uncovered a number of important clues that helped investigators better understand this amphibian mystery.
