Dolphins use “packets” of broadband clicks during long range echolocation tasks

Abstract

When echolocating, dolphins typically emit a single short duration, high-frequency, broadband “click,” then wait for the echo to return before emitting another click. However, previous studies have shown that dolphins and belugas performing long-range echolocation tasks may instead emit a burst, or “packet,” of several clicks, then wait for the packet of echoes to return before emitting another packet of clicks. The exact reasons for the use of packets, rather than individual clicks, is unknown. In this study, the use of packets by dolphins was examined by having trained bottlenose dolphins perform long-range echolocation tasks. The tasks featured the use of “phantom” echoes produced by capturing the dolphin’s outgoing echolocation clicks, convolving the clicks with the impulse response of a physical target to create an echo waveform, then broadcasting the delayed, scaled echo waveform back to the dolphin. Dolphins were trained to report the presence of phantom echoes or a change in phantom echoes. At ranges below 75 m, the dolphins rarely used packets of clicks. For ranges greater than 75 m, the likelihood of packet use was related to both target range and echo strength. [Work supported by the SSC Pacific Naval Innovative Science and Engineering (NISE) program.]