Meeting Abstract

64.1  Thursday, Jan. 6  Dip Listening: Do Frogs Do It? VELEZ, A.*; BEE, M.A.; University of Minnesota – Twin Cities velez011@umn.edu

The background noise generated in dense social aggregations, such as choruses or crèches, places constraints on communication. We know relatively little about how nonhuman animals may be adapted to exploit various acoustic features of signals and noise to facilitate signal recognition and discrimination in noisy environments. Human listeners, for instance, are able to detect speech cues at moments when the amplitude of the background noise dips to a low level, a phenomenon often referred to as “listening-in-the-dips.” In this study of gray treefrogs (Hyla chrysoscelis), we asked whether temporal fluctuations in the amplitude of chorus-like background noise affect the ability of females to recognize and discriminate male mating calls. In female phonotaxis experiments, we tested the hypotheses that temporal amplitude fluctuations in chorus-like noise influence (1) thresholds for recognizing male mating signals, and (2) the ability to discriminate between signals. Compared to an unmodulated control, signal recognition thresholds were ~4dB lower at low rates (0.625 Hz – 2.5 Hz) of sinusoidal amplitude modulation (SAM) and ~6dB higher at high SAM rates (40 Hz and 80 Hz). Temporal amplitude fluctuations had little effect on the ability of female frogs to discriminate calls varying in length. As predicted by signal detection theory, these results show that discrimination is a more difficult task than recognition. In addition, since natural sounds, including the sounds of frog choruses, are often modulated at slow rates, female frogs might benefit from dips in the background noise to recognize signals in natural social environments.