Herpetofaunal Inventories of the National Parks of South Florida and the Caribbean: Volume II. Virgin Islands National Park

Amphibian declines and extinctions have been documented around the world, often in protectednatural areas. Concern for this alarming trend has focused attention on the need to document all species ofamphibians that occur within U.S. National Parks and to search for any signs that amphibians may bedeclining. This study, an inventory of amphibian species in Virgin Islands National Park, was conductedfrom 2001 to 2003. The goals of the project were to create a georeferenced inventory of amphibianspecies, use new analytical techniques to estimate proportion of sites occupied by each species, look forany signs of amphibian decline (missing species, disease, die-offs, etc.), and to establish a protocol thatcould be used for future monitoring efforts.Several sampling methods were used to accomplish these goals. Visual encounter surveys andanuran vocalization surveys were conducted in all habitats throughout the park to estimate the proportionof sites or proportion of area occupied (PAO) by amphibian species in each habitat. Line transect methodswere used to estimate density of some amphibian species and double observer analysis was used to refinecounts based on detection probabilities. Opportunistic collections were used to augment the visualencounter methods for rare species. Data were collected during four sampling periods and every majortrail system throughout the park was surveyed.All of the amphibian species believed to occur on St. John were detected during these surveys.One species not previously reported, the Cuban treefrog (Osteopilus septentrionalis), was also added tothe species list. That species and two others (Eleutherodactylus coqui and Eleutherodactylus lentus) bringthe total number of introduced amphibians on St. John to three. We detected most of the reptile speciesthought to occur on St. John, but our methods were less suitable for reptiles compared to amphibians.No amphibian species appear to be in decline at this time. We found no evidence of disease or ofmalformations. Our surveys provide a snapshot picture of the status of the amphibian species, socontinued monitoring would be necessary to determine long-term trends, but several potential threats toamphibians were identified. Invasive species, especially the Cuban treefrog, have the potential to decreasepopulations of native amphibians. Introduced mammalian predators are also a potential threat, especiallyto the reptiles of St. John, and mammalian grazers might have indirect effects on amphibians and reptilesthrough habitat modification. Finally, loss of habitat to development outside the park boundary couldharm some important populations of amphibians and reptiles on the island.

This document was submitted by the Florida Cooperative Fish and Wildlife Research Unit. Revised and reprinted 2005