Temporal Variation in Anuran Calling Behavior: Implications for Surveys and Monitoring Programs
Recent awareness of amphibian declines has raised the need for effective monitoring programs. Call surveys are a standard approach to monitoring populations of most anuran species. Temporal variation in calling activity, however, may result in failure to detect some species. Automated recording systems (ARS) allow consistent sampling for extended periods with little or no disturbance to calling anurans. We used an ARS to measure temporal variation in anuran calling activity during the summer of 1997 at a Carolina bay on the U.S. Department of Energy's Savannah River Site, South Carolina. We documented considerable interspecific variation in calling activity, a phenomenon that, using traditional call survey techniques, would result in failure to detect some species. In particular, we found that Southern Leopard Frogs (Rana sphenocephala), thought to breed only in early spring and fall in the region, called consistently from midnight until dawn during July. Because protocols for most call surveys dictate that the listener survey only during early evening hours, most call surveys would not detect the presence of this species. Our results indicate that temporal variation in anuran calling activity warrants further investigation and should be considered when developing anuran monitoring programs.Abstract

Calling anuran species recorded over the 26-day study. Note consistency of Hyla cinerea, Rana clamitans, Aris gryllus, and R. catesbeiana

Daily calling patterns in Acris gryllus and Gastrophryne carolinensis. Mean calling activity was calculated by averaging the recorded calling activity levels for each 30-min time period over all days of the study. Error bars denote ± SD. Acris gryllus called all day, whereas G. carolinensis called primarily in the late afternoon and early evening

Daily calling patterns in the genus Hyla. Mean calling activity was calculated by averaging the recorded calling activity levels for each 30-min time period over all days of the study. Error bars denote ± SD. Most calling occurred between sunset and midnight

Daily calling patterns in the genus Rana. Mean calling activity was calculated by averaging the recorded calling activity levels for each 30-min time period over all days of the study. Error bars denote ± SD. Note that the most intense calling occurred between midnight and dawn