An important aspect of hearing and acoustic communication is the ability to discriminate differences in sound level. Little is known about level discrimination in anuran amphibians (frogs and toads), for which vocal communication in noisy social environments is often critical for reproduction. This study used two-choice phonotaxis tests to investigate the ability of females of Cope's gray treefrog (Hyla chrysoscelis) to discriminate between two advertisement calls differing only in sound pressure level by 2, 4, or 6 dB. Tests were conducted in the presence and absence of chorus-shaped noise (73 dB) and using two different ranges of signal levels (73-79 dB and 79-85 dB). Females discriminated between two signals differing by as little as 2-4 dB. In contrast to expectations based on the "near miss to Weber's law" in birds and mammals, level discrimination was slightly better at the lower range of signal amplitudes, a finding consistent with earlier studies of frogs and insects. Realistic levels of background noise simulating a breeding chorus had no discernable effect on discrimination at the sound level differences tested in this study. These results have important implications for studies of auditory masking and signaling behavior in the contexts of anuran hearing and sound communication.
Bibliographical noteFunding Information:
We thank M. Linck and the Three Rivers Park District for generous access to study sites, D. Pereira and the Minnesota Department of Natural Resource for permission to collect frogs, D. Bankwala, K. Bocklund, N. Buerkle, R. Carter, M. Caldwell, B. Chicoine, I. Fridman, J. Henly, M. Johnson, M. Kelly, J. Kleinschmidt, B. Linehan-Skillings, K. McGuire, S. Peterson, and especially S. Tekmen for help collecting and testing frogs, and an anonymous reviewer for helpful feedback on the manuscript. This work was supported by NIDCD 5R01DC009582.
© 2012 Acoustical Society of America.