The call behavior seen here has been
identified as a blue whale calling behavior in the literature (see
Aroyan et al.). The only time it occurs in Pioneer Seamount data is in
day 245 of 2001, between 4 am and 2 pm. These D type vocalizations appear
highly variable and seem to occur within the proximity of multiple individuals.
Blow-up of the repeated type B call.
This blue whale conversation
took place the day after the installation of the underwater cable.(Time axis in seconds.)
It has been proposed by Aroyan
et al. that in vocalization by blue whales the air-filled cavity
formed by the laryngeal sac and nasal passages effectively forms a
Helmholtz oscillator, as shown above.Air
flows through an oscillating valve driving the resonant oscillation of
the cavity.In order to produce
sustained low-frequency moans -such as the B call - this
model suggests that the necessary differential pressure on the
lungs must come from the act of diving.
Blue whales typically produce
sequences of several equally spaced calls or call pairs,
separated by a breathing interval (McDonald et al., shown
to the left).In the case of the A-B
calling sequences, a reasonable hypothesis would be that one
call is produced during the descent, when air passes from the
collapsing lungs into the nasal passages and laryngeal sac,
and the paired call is produced as the whale returns to its original
depth.CritterCam observations (shown to
the left) indicate a pattern during feeding with a rapid descent and ascent,
followed by a pause.While calling may
be separate from feeding, the (descent, ascent, pause) pattern could
correspond to the (A, B, pause) pattern of the AB calling
Several other acoustic
features of the calls may have implications for the mechanism.The A call starts and ends with a tone very
similar to the B call; in between, short segments at the B-call
frequency alternate with pulses at 90 Hz some sort of
valving mechanism is suggested.
Graphics from Aroyan, McDonald, Webb, Hildebrand, Clark,
Laitman and Reidenberg, Acoustic Models of Sound Production and Propagation, in Hearing
by Whales and Dolphins, ed. Au, Popper
and Fay (Springer,2000) p. 409-469.
The most remarkable result of
our study is the reproducibility of the B call frequency.(The characteristics of the B call make it
possible to measure its central frequency very
accurately.)This frequency is the
same, within the accuracy of the measurement, for all calling whales
(large and small) and over a space of a year!Why do they need to call at the same frequency?And how do they do it?
While we do not have the
expertise to propose a model of cetacean hearing, we note that a
process of observing beats is suggested.The typical deviation of frequency that we observe is
0.09 Hz.This corresponds
to a one-cycle error in phase over 12 seconds.And frequency-matching by observing beats has a
sensitivity of roughly one cycle over the period of
The A call
C and B call
C call is always seen preceding the B call. The C call seems
only to occur in association with the A-B call pairs, but rarely contains
a significant amount of energy so it is not certain how often this
spectrogram of a typical A call has been de-noised, revealing the
time- frequency characteristics of each pulse. The pulses are comprised
of a ~1 sec upward sweep at the same central frequency of the
B calls followed by a 90Hz squeak of about 0.4 sec.
The whale seems to ramp up the power of its low-frequency call to
hit this non-harmonically related 90Hz note. The call then finishes
with a B type drone as if its clearing the air out of its
lungs and preparing for the B call or series of B calls
which always seems to follow an A call.
sharp call ?
This spectrogram, showing 20 minutes of
the loudest call sequence observed, reveals a feature not seen in
calls from more distant whales. The feature corresponds temporally to the
C call but occurs in the 250-350 Hz range. This feature
is only visible at these large scales because the signal is so weak and seems to be
dispersed over the 10 second length of the C call.
spectrogram shows half an hour of the most typical calling behavior. An A
call seems always to be followed by a B call 20-25 seconds later. A sequence
of 5-6 A-B call pairs is repeated at intervals of 125 seconds, between three-minute
breathing intervals. This type of behavior occurs for hours on end and
long after the whale is nearly out of range. Notice the faint calling of more distant
whales. The third-harmonic band seems to be filled with B calls
spectrogram, 30 minutes long, shows another abundant type of calling behavior.
A faint A call is followed by 7-16 B type calls spaced 50 seconds apart.
These B type calls are distinct because they are broken into two sections separated
by a 2 second gap. The spacing between each call is much shorter compared
to that of the typical A-B call pairs seen above.