Mass Mortality and Population Declines of Anurans at an Upland Site in Western Panama

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Abstract
I report an episode of anuran mortality and decline in the Reserva Forestal Fortuna, Chiriquí, Panama. The symptoms of decline at this site include population reductions, the presence of dead or dying adults, and tadpole abnormalities. Streamside anurans were abundant and diverse in 1993–1995, were restricted to a few streams in December 1996–January 1997, and then became rare throughout the reserve in July–August 1997. Between December 1996 and January 1997, I found 54 dead or dying frogs belonging to 10 species, and 12% of tadpoles had abnormalities of the oral disc. In July–August 1997 I monitored nine streams 37 times and captured only six individuals, whereas 13 terrestrial surveys along five trails resulted in 18 captured individuals. No dead or dying animals were found during those two months, but 11% of tadpoles had mouthpart abnormalities. Necropsies revealed that 18 of 18 dead anurans had a fungal infection of the skin; because this fungus was the only infection shared among all dead frogs, I suggest that it killed them and contributed to the decline of these populations. The presence of mouthpart abnormalities during a period of adult mortality suggests that this symptom may also be linked to the fungus infection. Clinical signs of decline in the anurans of Fortuna are similar to those found in the anurans of Monteverde and Las Tablas, Costa Rica, and I hypothesize that this pathogen was involved in the declines at all three sites.