Transcript 01010101 01010100101 01010101010 10101010

01010101
01010100101
01010101010
10101010
COMMUNICATION BY
BLUE WHALES???
cable
cable
ROMBERG TIBURON CENTER
BREAK
Pioneer Seamount
Observatory
OBSERVATION OF BLUE WHALE CALLS FROM PIONEER SEAMOUNT
Michael D. Hoffman,1 Newell Garfield,2 and Roger Bland1
1. Physics and Astronomy Department and Romberg Tiburon Center for Environmental Studies, San Francisco State University
2. Department of Geosciences and Romberg Tiburon Center for Environmental Studies, San Francisco State University
http://www.physics.sfsu.edu/~seamount
We have carried out a high-statistics study of the “B” call of the blue whale (Balaenoptera musculus), as observed from
the Pioneer Seamount underwater observatory, 90 km off the California coast. Data were collected in several contiguous
blocks, via an underwater cable, over a period of 13 months. The continuous operation and the non-invasive nature of the
observations make this a homogeneous and unbiased sample. We find a remarkable degree of consistency in the “B”
calling patterns of the blue whale: The calling interval is constant to 4% accuracy; and the frequency of calls is adjusted to
be the same, over long periods of time, and for all calling individuals, to an accuracy of 0.5 %. The calling frequency
itself is apparently changing with time, with all individuals visiting Pioneer Seamount tracking the change. Two
substantially different types of calling sequences are observed, each at the same frequency, each with its well-regulated
(but different) calling interval.
D
D
Underwater topography near Pioneer Seamount. (Graphic courtesy of
PMEL/NOAA)
A number of questions concerning blue-whale acoustic activity are raised. What types of behavior correspond to these
two calling sequences? What is the function of the precisely regulated call frequency? How do individuals of different
size
adjust
their DcallD to the same frequency? And what sense is able to perceive frequency to this remarkable accuracy?
D
D
D
D D
Contour map showing the location of Pioneer Seamount. (Graphic courtesy
of the Monterey Bay National Marine Sanctuary.)
And finally, is there any information transmitted by acoustic calling which is so remarkably invariant?
CALLING PATTERNS
183
183
183
183
183
183
183
183
238
127
143
131
126
190
168
149
128
227
161
138
151
137
183
242
130
136
132
132
137
128
138
197
130
133
128
140
141
199 sec
139sec
130 sec
136 sec
140 sec
191 sec
177 sec
125 sec
128 sec
128 sec
THE BLUE-WHALE “A” AND “B” CALLS
192 sec
135 sec
D
131 sec
183
183
183
Blue-whale sonorization consists mainly of two calls, referred to as the “A” call (a pulsing call) and the “B” call (a “moan” of steadily decreasing frequency.) Other, rarer calls are shown in the GALLERY to the right.
183
Other researchers have found several distinct calling patterns for Eastern Pacific
blue whales. The most prominent in our data are patterns of repeated “A”-”B”
call pairs (AB calling) and sequences of “B” calls alone (B-only calling). For
spectrograms of these sequences, see the GALLERY to the far right.
SEASONAL AND
DIEL VARIABILITY
90 Hz
A
16 Hz
B? A?
observatory off line
B? A?
The “A” call consists of a series of very regular pulsations, with two components, at different frequencies and out of phase in time. The high-frequency component
peaks at 90 Hz and shows little harmonic structure. The low-frequency component has most of its power near 16 Hz, the fundamental frequency of the “B” call. Most
“A” calls seem to have short sections before and after the pulsations sounding very much like the “B” call..
B
AB calling sequence (day 285, 2001). Note pattern of equally spaced AB pairs, separated by breathing intervals
B
B
B
harmonics
B
B
B
AB
AB
A B
AB
AB
AB
A B
A B
AB
A B A B
AB
AB
A B
A B
AB
A B
The clearest trends in these data are the absence of calls from
mid-April to mid-July, followed by plentiful calling through midNovember. There were more calls in 2001 than 2002, and the
calls were fainter in 2002. One simple explanation would be that
the whales stayed closer to shore in 2002, though we have no
other evidence for this hypothesis. [The ‘grayed-out’ points show the
AB
48 Hz
32 Hz
16 Hz
number of calls triggering the matched-filter detection. The black points
show the number of calls remaining after least-squares fitting. A manual
scan of spectrograms was carried out in addition for the 2002 data.]
The “B” call consists of a repeating waveform of extremely predictable frequency, about 16 Hz. The power at multiples of 16 Hz consists of harmonics of the
fundamental – the waveform departs increasingly from a perfect sinusoid as the power in the harmonics increases. The harmonic structure, and the envelope of the signal
(power versus time) vary in our data sample – especially in the “B-only” sequences. However, the fundamental frequency at the center of the call and the (slight) rate of
decrease of the frequency during the call are extremely reproducible, as described below.
“B-only” calling sequence (day 284, 2001). Note the closer spacing in the absence of the “A” call.
THE CONSTANT-FREQUENCY “B’ CALL
Calambokidis et al., 2002, CRITTERCAM data.
McDonald, Calambokidis, Teranishi and Hildebrand, JASA 109,
1728. Near Santa Barbara, Ca, Oct. 1997. “AB” sequences spaced
125-130 sec apart; “B-only” sequences spaced 45-55 seconds apart.
The “B” call of the blue whale is a contact call – it seems to be used by the whales to stay in contact with each other. This call is remarkable in at
least two respects. (1) All whales “tune” to the same frequency, with a pitch discrimination far better than that of humans. (2) This frequency
chosen by the group has steadily decreased over recent years. The determination of this frequency is described below. The average frequency
over the 13 month period studied here is 16.01 Hz, with a variance of the sample of 0.09 Hz. (This variance may be dominated by measurement
error.) From our data alone we determine a rate of decrease in this frequency of 0.08 Hz, in rough agreement with published observations.
Here the hour of the day (UT) is plotted vertically against the date, horizontally, for all 6984 triggers
from the matched-filter detection. There is no striking change in the day-night variation over the 13month period of this study.
dives spaced 500 sec apart
Lunges through krill layer, spacing
80 sec
AB calling: T= 128
sec, =8 sec
B-only calling: T =
50 sec, =3 sec
Time interval between B calls. The time to the following peak is shown on the x axis, and
the time on to the peak after that, on the y axis. The peaks are found by automatic pattern
recognition, so many peaks are missing. The prominent bands show the peak spacing of
about 125 sec for AB calling sequences and of about 50 sec, for B-only calling.
Histogram of time intervals. The main peak corresponds to the spacing between
peaks in AB sequences, with a peak at twice its value from cases where an
intermediate peak is missed by the pattern recognition. The lower peak shows the
peak spacing for B-only calling. Both times are extremely well defined.
AB
Spectrogram obtained from averaging waveforms for a sequence of loud calls. We have
represented the central 6 seconds of this call by a sinusoid with frequency decreasing with
time. The waveform from each of the 6984 calls identified using a matched filter was fit
using least squares to determine its central frequency (f0) and rate of decrease of the
frequency (alpha). The results are shown to the right.
Distributions in central “B”-call frequency and
chirp rate. For this 13-month period the average
frequency was 16.01 Hz, with a call-to-call
variance of 0.09 Hz. For the musically inclined,
16 Hz is exactly 4 octaves below Middle C, and
a deviation of 0.09 Hz corresponds to an interval
of 0.09 half-tones!!
Decline in call frequency over 13 months at
Pioneer Seamount. The rate of decrease
from this data alone is estimated at 0.08
Hz/year
Decline in call frequency over the last
10 years. The green line is the trend
from Pioneer Seamount data alone.
Help and advice is gratefully acknowledged from: Dave Mellinger, Chris Fox, Jonathan Klay, Andy Lau, and Haru Matsumoto, NOAA-PMEL Jim Mercer and Lyle Gullings, APL,
University of Washington; Ching-Sang Chiu, Monterey Naval Postgraduate School; and John Bourg and Jim Lockhart, San Francisco State University
Fitted frequency and sweep rate for the day 285, 2001 sequence of very
loud calls (red points) compared to a larger sample of calls from the
entire year’s data. The tighter grouping of this sample probably reflects
the smaller errors associated with the larger signals. The distribution of
red points is centered at (f0,) = (16.03 Hz, 0.06 Hz/sec), with widths of
( f0,  ) = (0.04 Hz, 0.01 Hz/sec).
6 pm PST
6 am PST
Diel variability of the rate of “B” call triggers. While calling is observed at all hours of the day, the
plot peaks in those hours corresponding roughly to the daylight hours in the Pacific Daylight time
zone. However, there are various possible biases which could lead to such an effect which we have
not so far excluded (for instance, a day-night difference in the ambient acoustic noise).