Volume 122, Issue 5, November 2007
Index of content:
- BIOACOUSTICS 
Stream ambient noise, spectrum and propagation of sounds in the goby Padogobius martensii: Sound pressure and particle velocitya)122(2007); http://dx.doi.org/10.1121/1.2783113View Description Hide Description
The most sensitive hearing and peak frequencies of courtship calls of the stream goby, Padogobius martensii, fall within a quiet window at around in the ambient noise spectrum.Acoustic pressure was previously measured although Padogobius likely responds to particle motion. In this study a combination pressure and particle velocity detector was utilized to describe ambient noise of the habitat, the characteristics of the goby’s sounds and their attenuation with distance. The ambient noise (AN) spectrum is generally similar for and (including the quiet window at noisy locations), although the energy distribution of spectrum is shifted up by . The energy distribution of the goby’s sounds is similar for and spectra of the Tonal sound, whereas the pulse-train sound exhibits larger differences. Transmission loss was high for sound and : energy decays , and sound ratio does not change with distance from the source in the nearfield. The measurement of particle velocity of stream AN and P. martensiisounds indicates that this species is well adapted to communicate acoustically in a complex noisy shallow-water environment.
The social vocalization repertoire of east Australian migrating humpback whales (Megaptera novaeangliae)122(2007); http://dx.doi.org/10.1121/1.2783115View Description Hide Description
Although the songs of humpback whales have been extensively studied, other vocalizations and percussive sounds, referred to as “social sounds,” have received little attention. This study presents the social vocalization repertoire of migrating east Australian humpback whales from a sample of 660 sounds recorded from 61 groups of varying composition, over three years. The social vocalization repertoire of humpback whales was much larger than previously described with a total of 34 separate call types classified aurally and by spectrographic analysis as well as statistically. Of these, 21 call types were the same as units of the song current at the time of recording but used individually instead of as part of the song sequence, while the other 13 calls were stable over the three years of the study and were not part of the song. This study provides a catalog of sounds that can be used as a basis for future studies. It is an essential first step in determining the function, contextual use and cultural transmission of humpback social vocalizations.
Estimated source intensity and active space of the American alligator (Alligator Mississippiensis) vocal display122(2007); http://dx.doi.org/10.1121/1.2785811View Description Hide Description
In this article the results are reported of a study to measure the intensity of the vocal displays of a population of American alligators (Alligator mississippiensis). It was found that the dominant frequencies in air range between 20 and with a sourcesound pressure level (SPL) of at . The active space for the air-borne component is defined by the background and was estimated to be in a range up to in the band. For the water-borne component the dominant frequency range was with a sourceSPL of at . The active space in water is defined by hearing thresholds and was estimated to range up to in the band. In the lowest frequency bands, i.e., , the estimated active space for otolith detection of near-field particle motion in water ranged to , which compared significantly with far-field detection for these frequencies. It is suggested that alligator vocal communication may involve two distinct sensory mechanisms which may subserve the functions of scene analysis and reproduction, respectively.
Onset, growth, and recovery of in-air temporary threshold shift in a California sea lion (Zalophus californianus)122(2007); http://dx.doi.org/10.1121/1.2783111View Description Hide Description
A California sea lion (Zalophus californianus) was tested in a behavioral procedure to assess noise-induced temporary threshold shift (TTS) in air. Octave band fatiguing noise was varied in both duration and level ( re ) to generate a variety of equal sound exposure level conditions. Hearing thresholds were measured at the center frequency of the noise before, immediately after, and following exposure. Threshold shifts generated from 192 exposures ranged up to . Estimates of TTS onset [ re ] and growth ( of TTS per dB of noise increase) were determined using an exponential function. Recovery for threshold shifts greater than followed an per linear function. Repeated testing indicated possible permanent threshold shift at the test frequency, but a later audiogram revealed no shift at this frequency or higher. Sea lions appear to be equally susceptible to noise in air and in water, provided that the noise exposure levels are referenced to absolute sound detection thresholds in both media. These data provide a framework within which to consider effects arising from more intense and/or sustained exposures.