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Fig. 4. (A) Clicks and echoes displayed in an echogram from a 250 s time span
during the acoustically active part of a Mesoplodon dive. Time is on
the x-axis, and the y-axis gives the time elapsed from the
emitted click to the returning echoes expressed as target range by using the
two-way-travel time at a sound speed of 1485 m s-1 akin to the
upside-down display of an echosounder. The dense line at time 0 on the
y-axis is the emitted clicks that trigger the beginning of the time
window. Sound intensity is indicated by the color, so that yellow is strong
and blue is weak. Note the many trains of incoming echoes throughout the
sequence, and the bottom echoes emerging between 48 and 95 s. (B) Expanded
version of the first 25 s shown in A, showing that the whale at times passes
through clouds of echo sources without engaging in capture attempts. (C)
Expanded version of 16 s shown in A, showing a click train with echoes from an
approaching prey target that is terminated by a buzz during capture. The
target echoes disappear right at the buzz and reappear around 224 s during the
buzz. Note that the ICIs of the buzz are so short that the clicks are
displayed repeatedly like harmonics within a time span of 26 ms corresponding
to a two-way-travel path of 20 m.
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