Assessing the Use of Call Surveys
to Monitor Breeding Anurans in Rhode Island

William B. Crouch III  
Stroud Water Research Center, Avondale, Pennsylvania 19311, USA.

Peter W. C. Paton
Department of Natural Resources Science, University of Rhode Island, Kingston, Rhode Island, 02881, USA.

ABSTRACT.-Our objective was to develop a long-term monitoring program that quantified anuran population trends in Rhode Island.  Since road-based, manual call surveys are widely used in North America to monitor anurans, we assessed the efficacy of using this method to monitor the impact of anthropogenic change of anuran populations in the state.  We quantified interspecific variation in calling chronology, calling frequency, and calling intensity at 31 breeding ponds in southern Rhode Island in 1998.  Four distinct sampling periods were needed to monitor the seven species we detected.  During a species' peak sampling period, males of some species called only sporadically within our 16-min surveys, such as pickerel frogs (Rana palustris), while other species called continually (spring peepers [Pseudacris crucifer] and green frogs [Rana clamitans]). Based on accumulation curves, we suggest that call surveys in Rhode Island be conducted for 10-min at breeding ponds to have a high probability of detecting all species.  Assuming we conducted one call survey annually during the four sampling periods, a power analysis estimated that we need to conduct 283 or 690 10-min surveys annually to detect 10% or 5% annual declines, respectively, to monitor most anurans in Rhode Island.  Common species that are widespread and call frequently could be monitored with road-based call surveys.  However, rarer species or those that call infrequently would be difficult to monitor with call surveys in Rhode Island, therefore other monitoring methods might be more appropriate.