Abstract:
The interpulse-intervals, 3-D-head-attitudes, azimuths, and pulse waveforms of two Atlantic bottlenose dolphins were recorded while they searched successive circular bottom areas of 80-yd radii in the open ocean to echolocate bottom objects at depths of 40--50 ft. The animals remained near the center of the area while searching the bottom for 8-in., half-tri-planes on steel plates with both the location of animals and objects determined by a high-accuracy GPS. The animals were rewarded for correctly reporting the presence or absence of objects that were placed at a random 50% of the stations and, where present, randomly distributed over station area. The derived scan patterns and pulse spectra provide a systematic description of open-ocean echolocation of bottom objects. As in previous work with water-column objects in a single field, these animals adapted their spatial distributions of ensonification to their recent experience with detected objects (i.e., the search area). Head orientation and interpulse intervals were correlated with object location on object-present trials while analysis of the pulses-on-object as a function of distance, echo-to-pulse delays, and consistency of the pulse spectra showed important differences between the open-water test scenario and the more traditional tests with animal and targets in static positions.