Bottlenose dolphin short-range communication in a shallow, noisy environment
Jensen, F., Beedholm, K., Wahlberg, M., Bejder, L. and Madsen, P.T. (2010) Bottlenose dolphin short-range communication in a shallow, noisy environment. The Journal of the Acoustical Society of America, 128 (4). p. 2467.
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Bottlenose dolphins use frequency-modulated whistles to convey information to conspecifics. The detection range of a signal depends on the source and receiver properties, the background noise level, and the sound propagation characteristics of the environment. The probability of detecting a signal can be modeled if these variables are known. Here we measured source levels and propagation loss of whistles from bottlenose dolphins in a shallow-water environment with high ambient noise levels dominated by snapping shrimp. A dispersed array of GPS-synchronized hydrophones was used to record whistles. Signals were localized acoustically using time-of-arrival differences of the same whistle derived by cross-correlating each channel with one recorded instance of the whistle, suitably filtered with a time-varying filter matching the fundamental time-frequency contour. Acoustic localization allowed for calculation of source levels and spectral content. Subsequently, background noise levels were measured and environmental sound propagation characteristics quantified using transmission experiments with pure tones and sweeps. Using the passive sonar equation, the active space of whistles in this habitat was estimated around 640–1150 m depending on whistle type, indicating that the effective communication range of dolphins in this habitat is an order of magnitude below previous estimates. Acoustic and ecological perspectives of these conclusions are discussed.
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