Fig. 3. Bimodal sound production in Mesoplodon. Apparent output (AO) plotted against the corresponding interclick interval (ICI) for 5000 clicks from sequences randomly picked for both of the tagged animals. Regular clicks have ICIs between 200 and 500 ms with an emphasis around 400 ms. Buzz clicks have apparent outputs 15-20 dB lower and ICIs between 5 and 20 ms. Note the few intermediate data points between the two clusters of regular and buzz clicks, emphasizing the rapid transition between the regular click mode and the buzz mode of the sound generator.