Previous research has shown some anuran species alter calling behavior in response to anthropogenic noises. The altering of calls due to anthropogenic noise could therefore have negative effects on breeding behavior of frogs. The purpose of our study was to test for differences in call frequency, note duration, and loudness of spring peeper (Pseudacris crucifer) calls at sites of varying distances from anthropogenic noise sources (i.e., roads). For this study, we set out acoustic recorders at six different sites of varying anthropogenic noise, classified by distance to road noise. Recorders were set out for a duration of approximately 4 weeks (March-April 2021), recording dusk to dawn. Audio recordings were analyzed using the software program Raven pro version 1.6 and call duration (s), max frequency (Hz), and other relevant acoustic parameters were compared between sites. Prior to analysis, files were filtered and only files containing spring peeper calls were used, then 3, 10-minute files were selected for each day. Of the 3 files a 1-minute section was randomly selected for analysis. Only non-overlapping calls were used for our analysis.
Anthropogenic noise was significantly different among research sites with mean peak power density ranging from 54.4 to 75.5 dB among the different sites. When comparing acoustic features of P. crucifer calls, we found a significant effect of site on max frequency, note duration, and peak power density (p< 0.001). Frogs located at sites with the greatest amount of anthropogenic noise tended to make calls with greater maximum frequencies and note length tended to be shorter than sites with low anthropogenic noise. Call peak power density, while significantly different among sites did not appear to be significantly related to the amount of anthropogenic noise. Therefore, site-related differences were not likely the result of the Lombard effect. These results are similar to previous studies on spring peepers which suggested that they modulate their call structure in response to interfering noise.