Assessing long-term population trends of wood frogs using egg-mass counts

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In North America, most efforts to monitor pond-breeding anurans have focused on call surveys. Egg-mass counts offer an alternative monitoring strategy that has been used extensively in Europe because this technique can produce precise and accurate estimates of annual reproductive effort at many study sites. We surveyed egg masses of Wood Frogs (Lithobates sylvaticus) at 18 ponds for up to 16 years from 1993-2008 in the largest contiguous forest tract in southern New England. We detected an average of 441.5 ± 343.7 egg masses per pond. Based on annual egg-mass counts, coefficients of variation (CV) were slightly higher than previous estimates for this species. We detected no relationship between mean annual population size and CV or between length of time series and CV. Population fluctuations in these ponds exhibited evidence of annual synchrony, in part because annual fluctuations at individual ponds were large enough that it was difficult to assess differences in population trends among ponds. However, the overall trend suggests this population was probably increasing slightly, which was expected because ponds were located in contiguous forest that remained intact during the study. Egg-mass counts appear to represent a feasible technique to monitor Wood Frog populations, given that all local breeding ponds are monitored. © 2011 Society for the Study of Amphibians and Reptiles.

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Journal of Herpetology