Echolocation in the Risso’s dolphin, Grampus griseus

This study investigated whether the Rissos dolphin, Grampus griseus, echolocates. The Rissos dolphin is a gregarious, near‐shore pelagic delphinid that consumes nearly exclusively cephalopods and has a distinctive groove along its forehead. In this study, an individual female Rissos dolphin was trained to discriminate an aluminum cylinder from a nylon sphere (Experiment 1) or an aluminum sphere (Experiment 2). The animal wore eyecups and was required to swim to and touch the standard cylinder. The animals choice accuracy was 98.3% in Experiment 1 and 99.6% in Experiment 2, indicating that she was able to perform the target discriminations with little difficulty despite being blindfolded. Clicks were acquired at amplitudes up to 202 dB (M=199 dB), peak frequencies up to 105 kHz (M=51 kHz), center frequencies up to 70–75 kHz (M=57 kHz), bandwidths of 31 to 92 kHz, and durations of 40–70 ms. The data establish that the Rissos dolphin echolocates and that its clicks are very similar to the clicks of other echolocating dolphins. Implications of the unique behavioral and physical characteristics of this species on its sonar system are discussed.