Calibrating Abundance Indices of Red Back Salamanders at Harvard Forest 2014

Herpetologists and conservation biologists frequently use convenient and cost-effective, but less accurate, abundance indices (e.g. artificial cover boards or natural objects surveys) in lieu of more accurate but costly and destructive population size estimators to detect and monitor size, state, and trends of amphibian populations. Despite advantages and disadvantages to each approach, studies calibrating abundance indices so they can be used as reliable population estimators are rare. We calibrated indices based on surveys under artificial cover boards and natural objects with a more accurate estimator of population sizes of red back salamanders (Plethodon cinereus (Green)) in a New England forest. Plethodon cinereus is an ecologically significant indicator species of forest dynamics, and accurate calibration of these indices should increase their reliability for monitoring programs. Average density/m2, capture probability, relative density of both natural objects searches, and cover board observations of P. cinereus in 30 × 30-m plots at the Harvard Forest (Petersham, Massachusetts, USA) were similar in stands dominated by Tsuga canadensis (eastern hemlock) and deciduous hardwood species (predominantly Quercus rubra [red oak] and Acer rubrum [red maple]). Abundance indices based on both cover board and natural object surveys were able to be calibrated using density estimates of P. cinereus derived from depletion (removal) surveys. The cover board index underestimated the estimated density of P. cinereus by 40%, but the natural object survey underestimated it by about 55%. We conclude that when calibrated and used appropriately, abundance indices can provide cost-effective and reliable measures of P. cinereus abundance that may be used in conservation assessments and long-term monitoring of northeastern USA forests.