Beam patterns of the dolphin demonstrate task-dependent dynamics

Abstract

The echolocation beam of the bottlenose dolphin was first carefully described by Au and colleagues (1978)[“Propagation of Atlantic bottlenose dolphin echolocation signals,” J. Acoust. Soc. Am. 64, 411-422] using various hydrophone array configurations and targets located in front of the dolphin and along its longitudinal axis. Measured beams were described as vertically elevated with mean vertical and horizontal 3-dB beamwidths of ~10°. The experimental paradigm was later augmented with denser hydrophone arrays, greater spatial coverage of the acoustic field, and the training of target detection with targets presented to the left or right of the dolphin’s longitudinal axis. Utilizing two dolphins, beam steering capabilities and beamwidth control were demonstrated. The two dolphins steered the axis of the echolocation beam up to 18° and 28° in the horizontal plane. Horizontal beamwidths were bimodally distributed in one dolphin, with peaks at 16° and 26°. The other dolphin had a unimodal distribution of beamwidths (peak at ~25°), likely reflecting a learned strategy for the off-axis detection task. The use of dense hydrophone arrays and challenging echolocation tasks continue to build on the work of Au and colleagues, who provided a paradigm that has greatly contributed to our understanding of dolphin biosonar.