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The directional properties of bottlenose dolphin clicks, burst-pulse, and whistle signals were measured using a five element array, at horizontal angles of 0°, 45°, 90°, 135°, and 180° relative to a dolphin stationed on an underwater biteplate. Clicks and burst-pulse signals were highly directional with directivity indices of ~11 dB for both signal types. Higher frequencies and higher amplitudes dominated the forward, on-axis sound field. A similar result was found with whistles, where higher frequency harmonics had greater directivity indices than lower frequency harmonics. The results suggest the directional properties of these signals not only provide enhanced information to the sound producer (as in echolocation) but can provide valuable information to conspecific listeners during group coordination and socialization.
Branstetter et al. (Wed,) studied this question.