Abstract
The odontocete sound production system is complex and composed of tissues, air sacs, and a fatty melon. Previous studies suggested that the emitted sonar beam might be actively focused, narrowing depending on target distance. In this study, we further tested this beam focusing hypothesis in a false killer whale (Pseudorca crassidens) in a laboratory setting. Using three linear arrays, we recorded the same emitted click at 2, 4, and 7 m distance while the animal performed a target detection task with the target distance varying between 2, 4, and 7 m. For each click, we calculated the beamwidth, intensity, center frequency, and bandwidth as recorded on each array. As the distance from the whale to the array increased, the received click intensity was higher than predicted by spreading loss. Moreover, the beamwidth varied with range as predicted by the focusing model and contrary to a piston model or spherical spreading. These results support the hypothesis that the false killer whale adaptively focuses its sonar beam according to target range. [Work supported by ONR and NSF.]