Audiograms of Chilean species of amphibians and their relevance for the evaluation of effects of anthropogenic noise

Abstract

Anuran amphibians use acoustic communication in breeding contexts, they are also the most threatened at the global level, with extreme declination rates. Thus, it is of particular interest to determine how the alteration of the sound environments by human intervention or anthropophonies affect them. Knowing the auditory sensitivity of animals is fundamental to assess the vulnerability of organisms to noises generated by anthropic activity. This study reviews and compares auditory thresholds of six species of native anurans measured in previous researches with simulations of machine noises at different distances from these sound sources. Measurements of auditory thresholds by means of electrophysiological techniques show that the auditory range of these vertebrates is between frequencies of 0.1 to 5 kHz, with two zones of higher sensitivity, below 0.5 kHz and between 1-2 kHz, corresponding to sound detection by the two auditory receptors of the anuran internal ear, the amphibian and basilar papilla, respectively. The lowest auditory thresholds for these two frequency ranges are 41-49 and 37-54 dB SPL, respectively, indicating that sound reception is impaired by machine noise in the high frequency range, corresponding to the spectral zone of the calls with which these anurans communicate, but low frequency range is also impaired. Simulation of acoustic barriers prevents in part noise interference of high frequencies, but is not effective to preserve low frequency reception. These evidences are relevant for further evaluations of the impact of anthropophonies in native species.