4. Acoustic Communication in Whales and Dolphins
203
with another group from a long distance away. Up calls have acoustic features well suited to this function. They are the loudest of the calls, with a
spectral peak between 100 and 200 Hz, where the ambient noise of the
shallow water habitat reaches a minimum (Fig. 4.13). They also include the
acoustic feature of instantaneous narrowband frequency modulation, which
increases a signal's range of detection by increasing its time-bandwidth
product.
3.2.3 Blue and Fin Whales
Of all cetaceans, blue and fin whales produce the lowest frequency signals.
The lowest frequency signals known are the long moans of blue whales,
Balaenoptera musculus. The sounds of blue whales have fundamental
frequencies in the 14 to 36Hz band, below what humans can hear, and these
moans last several tens of seconds (Cummings and Thompson 1971; Edds
1982; McDonald et al. 1995; Thompson et al. 1996; Clark and Fristrup 1997;
Stafford et al. 1998). There are predictable differences in the calls of blue
whales from different ocean basins (Clark and Fristrup 1997). Figure 4.15
illustrates several of these calls of blue whales from different oceans. The
top spectrogram shows several phrases for a typical blue whale
call sequence recorded from the eastern North Pacific using the Navy's
Integrated Underwater Sound Surveillance System (IUSS). The first part of
a phrase is an amplitude-modulated tone with a strong fifth harmonic
evident as a band of energy around 90 Hz; the second part is a harmonically
rich frequency-modulated tone with a 1705Hz fundamental. These two
sounds are referred to as the A and B types, respectively (Thompson et al.
1996). This whale produced a sequence of pulses typical of blue whales in
the eastern North Pacific, where the pulse sequence includes an amplitudemodulated 90Hz downsweep followed by three calls at about 17Hz, then
a 90 Hz downsweep followed by one 17 Hz call. The bottom spectrogram
shows a typical call from the western North Atlantic also recorded using
IUSS. This whale produced steady regular sequences of 20 to 25-sec calls,
where a sequence lasted 12 to 15 min and consisted of repetitions of a
constant frequency tone at 19.6Hz followed by a frequency-modulated
downsweep to approximately 16Hz. Finback whales, Balaenoptera
physalus, produce pulses with energy in a range roughly between 15 and
30 Hz (Watkins et al. 1987), near the lowest frequencies that humans can
hear. Each finback pulse lasts on the order of one second and contains about
20 cycles. The source level of the pulses ranges from about 170 to 180 dB re
l/lPa at 1 m (Patterson and Hamilton 1964). Particularly during the breeding season in mid-latitudes, finbacks produce series of pulses in a regularly
repeating pattern in bouts that may last many days (Watkins et al. 1987).
Figure 4.16 illustrates two pulses out of one of these regular series.
These loud low-frequency sounds appear to be specialized for long-range
propagation in the sea. Absorption is negligible at the frequencies of these
203
with another group from a long distance away. Up calls have acoustic features well suited to this function. They are the loudest of the calls, with a
spectral peak between 100 and 200 Hz, where the ambient noise of the
shallow water habitat reaches a minimum (Fig. 4.13). They also include the
acoustic feature of instantaneous narrowband frequency modulation, which
increases a signal's range of detection by increasing its time-bandwidth
product.
3.2.3 Blue and Fin Whales
Of all cetaceans, blue and fin whales produce the lowest frequency signals.
The lowest frequency signals known are the long moans of blue whales,
Balaenoptera musculus. The sounds of blue whales have fundamental
frequencies in the 14 to 36Hz band, below what humans can hear, and these
moans last several tens of seconds (Cummings and Thompson 1971; Edds
1982; McDonald et al. 1995; Thompson et al. 1996; Clark and Fristrup 1997;
Stafford et al. 1998). There are predictable differences in the calls of blue
whales from different ocean basins (Clark and Fristrup 1997). Figure 4.15
illustrates several of these calls of blue whales from different oceans. The
top spectrogram shows several phrases for a typical blue whale
call sequence recorded from the eastern North Pacific using the Navy's
Integrated Underwater Sound Surveillance System (IUSS). The first part of
a phrase is an amplitude-modulated tone with a strong fifth harmonic
evident as a band of energy around 90 Hz; the second part is a harmonically
rich frequency-modulated tone with a 1705Hz fundamental. These two
sounds are referred to as the A and B types, respectively (Thompson et al.
1996). This whale produced a sequence of pulses typical of blue whales in
the eastern North Pacific, where the pulse sequence includes an amplitudemodulated 90Hz downsweep followed by three calls at about 17Hz, then
a 90 Hz downsweep followed by one 17 Hz call. The bottom spectrogram
shows a typical call from the western North Atlantic also recorded using
IUSS. This whale produced steady regular sequences of 20 to 25-sec calls,
where a sequence lasted 12 to 15 min and consisted of repetitions of a
constant frequency tone at 19.6Hz followed by a frequency-modulated
downsweep to approximately 16Hz. Finback whales, Balaenoptera
physalus, produce pulses with energy in a range roughly between 15 and
30 Hz (Watkins et al. 1987), near the lowest frequencies that humans can
hear. Each finback pulse lasts on the order of one second and contains about
20 cycles. The source level of the pulses ranges from about 170 to 180 dB re
l/lPa at 1 m (Patterson and Hamilton 1964). Particularly during the breeding season in mid-latitudes, finbacks produce series of pulses in a regularly
repeating pattern in bouts that may last many days (Watkins et al. 1987).
Figure 4.16 illustrates two pulses out of one of these regular series.
These loud low-frequency sounds appear to be specialized for long-range
propagation in the sea. Absorption is negligible at the frequencies of these