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First published online December 1, 2006
Journal of Experimental Biology 209, 5038-5050 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02596
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Foraging Blainville's beaked whales (Mesoplodon densirostris) produce distinct click types matched to different phases of echolocation

M. Johnson1,*, P. T. Madsen1,2, W. M. X. Zimmer3, N. Aguilar de Soto4 and P. L. Tyack1

1 Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
2 Department of Zoophysiology, University of Aarhus, Denmark
3 NATO Undersea Research Centre, V. le San Bartolomeo 400, 19126 La Spezia, Italy
4 Department of Animal Biology, La Laguna University, La Laguna 38206, Tenerife, Spain


Figure 1
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  		Fig. 1. Dive profile of a Blainville's beaked whale foraging dive showing vocal events.

 

Figure 2
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  		Fig. 2. (A) Waveform of a regular click from an untagged Blainville's beaked whale, as recorded by the DTAG. (B) Normalized power spectrum of the same click (solid line) and of an echo from a target ensonified by a regular click from the tagged whale (broken line). The dotted line is the system and ambient noise floor. (C) Time-frequency (Wigner) distribution of the click in A.

 

Figure 3
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  		Fig. 3. Variation in magnitude and waveform in a click sequence recorded from an untagged whale. (A) Peak envelope level of each click. Clicks with a single pulse are indicated by open dots; solid dots indicate clicks with two or more pulses. (B) Absolute value of the normalized cross-correlation functions of an on-axis click with two clicks from the sequence (indicated in A by triangles). (C) Normalized cross-spectral magnitude of clicks in a second sequence. Each spectrum is the Fourier transform of a click matched-filtered with an on-axis click. The spectra are displayed in ascending order of peak envelope level, i.e. the strongest clicks in the sequence are shown to the left. The dots on the right-hand side have the same interpretation as for A. Note the smooth cross-spectra of the strong, mono-pulsed clicks while weaker multi-pulsed clicks have more variable spectra.

 

Figure 4
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  		Fig. 4. On-axis and off-axis waveforms and spectra of buzz clicks. (A) Waveform of buzz click from an untagged whale judged to be on-axis. (B) Presumed off-axis buzz click from the same sequence (note the change in amplitude scale). (C) Spectra of the on-axis click (solid line), off-axis click (dot-dash line), an echo return from a tagged whale buzz click (broken line), and the noise floor (dotted line).

 

Figure 5
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  		Fig. 5. ICI sequence of buzz clicks in ten buzzes produced by the tagged whale. Although the duration of the buzzes varies, the pattern of ICI variation is quite stereotyped.

 

Figure 6
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  		Fig. 6. Echogram during the start of a buzz showing the hand-off from regular clicks (those before click `0') and buzz clicks. Each vertical slice of the echogram contains the outgoing click (at TWTT 0) and the subsequent echo returns. Pixel darkness indicates amplitude (the darker the pixel the greater the amplitude). Of the three echo sequences apparent before the buzz, only one continues to be visible during the buzz. The hand-off distance for this target was 3.0 m using a nominal sound speed in seawater of 1500 m s-1.

 

Figure 7
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  		Fig. 7. Comparative sizes of predator, prey and echolocation signal for the big brown bat Eptesicus fuscus (left), Blainville's beaked whale Mesoplodon densirostris (center) and bottlenose dolphin Tursiops truncatus (right). The lengths of the signals are computed by multiplying the typical signal duration by the sound speed in the appropriate medium. If different length signals are produced during search and terminal approach, representative lengths of each are indicated.

 




© The Company of Biologists Ltd 2006