Bufo periglenes, the golden toad, is an endangered species endemic to Costa Rica. Every year from the early 1970s through 1987 golden toads have emerged from retreats to breed during April-June. The most recent known breeding episode occurred during April-May 1987; more than 1500 adults were observed at five breeding pools, but a maximum of 29 tadpoles metamorphosed from these sites. During April-June 1988-90, we found only 11 toads during surveys of the breeding habitat. To examine the species' apparent decline, we analyzed data on rainfall, water temperature, and pH of the breeding pools. Our baseline data on weather patterns and characteristics of the breeding habitat suggest that warmer water temperatures and less advective precipitation during dry season post-1987 may have produced adverse breeding conditions. The toads may be alive and hiding in retreats awaiting appropriate weather conditions. The apparent scarcity of toads may reflect a normal population response to an unpredictable environment. On the other hand, because other anurans with different breeding specializations seem to be declining from the area as well, one wonders whether warmer temperatures and dry conditions could be responsible for real population declines. Because the habitat is protected and pristine, potential causes of anuran declines such as habitat destruction, introduced predators, and collecting seem unlikely. Measurements of pH of the breeding pools, cloud water, and precipitation do not suggest acid precipitation effects, although we cannot rule out the possibility of environmental degradation some time prior to our measurements. Long-term monitoring programs combined with carefully controlled field experiments are needed to address factors responsible for declining amphibians.
