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Monitoring Terrestrial Salamanders: Biases Caused by Intense Sampling and Choice of Cover Objects

Abstract Arrays of wood cover boards are useful tools for studying and monitoring plethodontid salamander populations. However, little is known about the biases inherent in monitoring data collected from such arrays. We used Red-Backed Salamanders, Plethodon cinereus, to test for two potential biases associated with use of wood cover board arrays. First, we tested whether frequent sampling of arrays can cause reduced counts of salamanders, resulting in the appearance of population declines where none exist. Second, we tested whether salamanders found under wood cover boards differed from salamanders found under natural cover objects in terms of sex ratios, stage class ratios, and snout–vent length. We found that sampling cover boards daily substantially reduced salamander counts under cover objects and that this result was pronounced for adults but not for juveniles. We found no decrease in counts with sampling cover boards weekly as compared to sampling every three weeks. With respect to differences between salamanders found underneath cover boards versus natural cover objects, we found that samples from under cover boards contained higher proportions of adults and lower proportions of juveniles and hatchlings than did natural cover objects. This was true in both the spring and fall. There were no differences in sex ratios or in snout–vent length within stage classes for salamanders in cover boards versus natural cover objects. These results suggest that cover boards used for monitoring or for studies of ecology and behavior should be sampled no more than once per week if natural levels of movement and territoriality are desired. Additionally, although cover board arrays may be suitable for tracking relative changes in overall population size, bias among size classes may make cover boards less than ideal tools for studies of salamander demography.