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Vocalizations produced by humpback whale (Megaptera novaeangliae) calves recorded in Hawaii

  • Cetos Research Organization
  • Smultea Environmental Sciences, Preston, WA USA
  • Marine Acoustics, Inc.


Although humpback whale (Megaptera novaeangliae) calves are reported to vocalize, this has not been measurably verified. During March 2006, an underwater video camera and two-element hydrophone array were used to record nonsong vocalizations from a mother-calf escort off Hawaii. Acoustic data were analyzed; measured time delays between hydrophones provided bearings to 21 distinct vocalizations produced by the male calf. Signals were pulsed (71%), frequency modulated (19%), or amplitude modulated (10%). They were of simple structure, low frequency (mean=220 Hz), brief duration (mean=170 ms), and relatively narrow bandwidth (mean=2 kHz). The calf produced three series of "grunts" when approaching the diver. During winters of the years 2001-2005 in Hawaii, nonsong vocalizations were recorded in 109 (65%) of 169 groups with a calf using an underwater video and single (omnidirectional) hydrophone. Nonsong vocalizations were most common (34 of 39) in lone mother-calf pairs. A subsample from this dataset of 60 signals assessed to be vocalizations provided strong evidence that 10 male and 18 female calves vocalized based on statistical similarity to the 21 verified calf signals, proximity to an isolated calf (27 of 28 calves), strong signal-to-noise ratio, and/or bubble emissions coincident to sound.
Vocalizations produced by humpback whale (Megaptera
novaeangliae) calves recorded in Hawaii
Ann M. Zoidis
Cetos Research Organization, 11 Des Isle Avenue, Bar Harbor, Maine 04609
Mari A. Smultea
Smultea Environmental Sciences LLC, 29333 SE 64th Street, Issaquah, Washington 98027
and Cetos Research Organization, 29333 SE 64th St., Issaquah, Washington 98027
Adam S. Frankel
Hawaii Marine Mammal Consortium, P.O. Box 6107, Kamuela, Hawaii, 96738-6107
Julia L. Hopkins,
Andy Day,
and A. Sasha McFarland
Cetos Research Organization, 11 Des Isle Ave, Bar Harbor Maine 04609
Amy D. Whitt
and Dagmar Fertl
Geo-Marine, Inc., 2201 Avenue K, Suite A2, Plano, Texas 75074
Received 17 July 2007; revised 12 December 2007; accepted 27 December 2007
Although humpback whale Megaptera novaeangliae calves are reported to vocalize, this has not
been measurably verified. During March 2006, an underwater video camera and two-element
hydrophone array were used to record nonsong vocalizations from a mother–calf escort off Hawaii.
Acoustic data were analyzed; measured time delays between hydrophones provided bearings to 21
distinct vocalizations produced by the male calf. Signals were pulsed 71%, frequency modulated
19%, or amplitude modulated 10%. They were of simple structure, low frequency mean
=220 Hz, brief duration mean=170 ms, and relatively narrow bandwidth mean=2 kHz. The
calf produced three series of “grunts” when approaching the diver. During winters of the years
2001–2005 in Hawaii, nonsong vocalizations were recorded in 109 65% of 169 groups with a calf
using an underwater video and single omnidirectional hydrophone. Nonsong vocalizations were
most common 34 of 39 in lone mother–calf pairs. A subsample from this dataset of 60 signals
assessed to be vocalizations provided strong evidence that 10 male and 18 female calves vocalized
based on statistical similarity to the 21 verified calf signals, proximity to an isolated calf 27 of 28
calves, strong signal-to-noise ratio, and/or bubble emissions coincident to sound.
© 2008 Acoustical Society of America. DOI: 10.1121/1.2836750
PACS numbers: 43.80.Ka WWA Pages: 1737–1746
Humpback whales Megaptera novaeangliae produce
song, nonsong social vocalizations, and nonvocal, surface-
generated percussive sounds e.g., caused by breaches, fluke
slaps, pectoral fin slaps, etc. during migration e.g., Kibble-
white et al., 1966; Payne and McVay, 1971; Norris et al.,
1999; Dunlop et al., 2005, 2006; Dunlop and Noad, 2007,
on low-latitude winter breeding/calving grounds e.g., Payne
and McVay, 1971; Winn and Winn, 1978; Tyack, 1981, 1982;
Darling, 1983; Silber, 1986; Payne, 1983; Helweg et al.,
1992; Au et al., 2000, and on higher-latitude summer feed-
ing grounds e.g., Thompson et al., 1977; Jurasz and Jurasz,
1979; D’Vincent et al., 1985; Sharpe et al., 1998. Songs are
well-documented vocalizations produced by males predomi-
nantly on the wintering grounds where they appear to be part
of breeding displays e.g., Payne and McVay, 1971; Winn et
al., 1973; Tyack, 1981; Darling, 1983; Helweg et al., 1992;
Au et al.
, 2000; Darling and Bérubé, 2001; Darling et al.,
2006. Singers are typically alone but may also accompany
other whales including a mother and calf e.g., Tyack, 1981;
Darling, 1983; Glockner and Venus, 1983; Darling and
Bérubé, 2001. Songs are characterized by continuous, re-
petitive, highly structured phrases and themes that contain
units with harmonics above 15 kilohertz kHz and sounds
above 24 kHz Payne and McVay, 1971; Darling, 1983;
Payne, 1983; Helweg et al., 1992; Au et al., 2000, 2001,
2005, 2006; Fristrup et al., 2003; Potter et al., 2003.
On the wintering grounds, nonsong social vocalizations
have been documented among adults Tyack, 1981; Silber,
1986. In contrast to song, adult nonsong vocalizations i.e.,
“social sounds” are produced erratically variable through
time, often interrupted by silent periods, are unpredictable,
do not contain the rhythmic, consistent, and continuous pat-
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J. Acoust. Soc. Am. 123 3, March 2008 © 2008 Acoustical Society of America 17370001-4966/2008/1233/1737/10/$23.00
terning of song, and are known to range from 50 hertz Hz
to over 10 kHz, with dominant frequencies below 3 kHz Ty-
ack, 1981; Silber, 1986. Early publications on nonsong vo-
calizations in surface-active groups of wintering humpbacks
coined the term social sounds to describe that specific behav-
ioral context Payne, 1978; Tyack, 1982, 1983; Tyack and
Whitehead, 1983; Silber, 1986. These social sounds have
been reported to occur predominantly in groups of three or
more adults composed of a mature female accompanied by a
male “principal escort” and other males aggressively vying
for a position near her Tyack and Whitehead, 1983; Silber,
1986; Clapham et al., 1992. Common behaviors include
chasing, charging, inflated head lunges, underwater blows,
aggressive contact, and fast surface traveling e.g., Darling,
1983; Tyack and Whitehead, 1983; Baker and Herman,
1984. Although the full function of social sounds in these
surface-active groups remains uncertain, they appear to in-
voke approach or avoidance responses from other whales,
depending on sex and composition Tyack, 1983. They also
seem to signal aggression or agitation among males fighting
for dominance or proximity to a female Silber, 1986.
Despite numerous underwater and/or acoustic studies of
humpback whale groups containing a mother–calf pair in
Hawaiian waters e.g., Glockner and Venus, 1983; Tyack,
1983; Silber, 1986; Glockner-Ferrari and Ferrari, 1990; Zoi-
dis and Green, 2001; Cartwright, 2005; Zoidis et al., 2005,
only recently have vocalizations been attributed to individual
calves based on observational evidence and underwater
videoacoustic data recorded with a single omnidirectional
hydrophone Zoidis and Green, 2001; Pack et al., 2005; Zoi-
dis et al., 2005. Reported evidence includes vocalizations
recorded in closest proximity to a calf with no other whales
nearby, strong signal-to-noise ratio, and/or vocalizations pro-
duced coincident to underwater bubble production by the
calf. Although this is strong evidence that humpback calves
vocalize, it cannot be ruled out that the sounds did not come
from another source/whale that was nearby or not visible
i.e., the omnidirectional hydrophone used in those studies
could not provide measurable evidence, such as directional
bearings, linking acoustic data to a source
. Published docu-
mentation that individual calves of other baleen whale spe-
cies vocalize is limited to one calf from each of three differ-
ent species the first two of which were captive animals:
gray Eschrichtius robustus兲共Wisdom et al., 2001, Bryde’s
Balaenoptera edeni兲共Edds et al., 1993, and North Atlantic
right whales Eubalaena glacialis兲共Parks and Tyack, 2005;
Parks and Clark, 2007.
Dunlop et al. 2005, 2006 and Dunlop and Noad 2007
remotely recorded nonsong vocalizations among migrating
humpback mother–calf pairs and other groups with a calf off
eastern Australia using an array of five separately anchored
hydrophone buoys; however, it was not possible to differen-
tiate which individual vocalized. Dunlop and Noad 2007
collectively termed these and other nonsong vocalizations
recorded from any migrating humpback as “nonsong social
vocalizations,” although songs were also recorded. Vocaliza-
tions were further defined as being internally produced by a
whale, including sounds generated from the blowhole. For
the purpose of this paper and terminology consistency, we
use the term “nonsong vocalizations” for sounds attributed to
humpback calves that did not meet the aforementioned defi-
nition of song and were not percussively generated by body
contact with the water surface.
In this paper, directional acoustic data from a two-
element hydrophone array combined with underwater video
empirically confirm that a male humpback whale calf pro-
duced nonsong vocalizations. Additional data indicate that
both male and female calves vocalize. Descriptions of these
vocalizations are presented and compared to earlier reports
and vocalizations from calves of other large whale species.
Contexts of some calf vocalizations are also described.
Underwater humpback vocalizations and behavior were
recorded during the winters of 2001–2006 off southwest
Maui and Kauai, Hawaii. Data were collected by one or two
snorkelers off a 6 8 meter m inboard or outboard vessel
and by personnel above water. Divers used two systems: a
Panasonic GS200 and/or GS300 digital underwater video
camera equipped with a single omnidirectional hydrophone
Biomon BM 8263-3c mounted 1 m below the camera, hy-
drophone sensitivity to 80 kHz, and a two-element hydro-
phone array used one day in March 2006. The two-element
array consisted of two HTI MIN-96 hydrophones frequency
response 2 Hz to 30 kHz mounted 1.5 m apart on a bar
perpendicular to the optical axis of the camera. This configu-
ration was used to determine left–right bearings to the source
of sounds produced in mother–calf groups i.e., the offset of
a sound source from the plane between the two hydrophones
was measured by the time delay of the signal arriving at the
two hydrophones. The unit was held parallel to the waters
surface. A zero offset would indicate that the sound source
was equidistant from the two hydrophones and located on a
vertical plane parallel to the optical axis of the camera. Veri-
fication that sounds were produced by a calf for the two-
element array was defined as repeated measurements of sig-
nals within a 10° angle of the plane bisecting the two
hydrophones, with the calf centered in the video frame and
no other whales present in that plane. Frequency response
curves were obtained from the manufacturer specifications
for the hydrophones and recording equipment. Hydrophones
were calibrated by the manufacturer.
To analyze acoustic data, the recorded videotapes were
connected to an Apple Mac Mini and raw video data were
transferred to hard disk using the program
cordings were divided into a series of video clip files. The
digital video files were aurally and visually reviewed for po-
tential acoustic signals. Visual inspection of spectrograms
was useful, particularly if signals were low frequency or
pulsed. All digital video clips with audible pulses were ex-
ported as audio interchange file format files. Clips down-
loaded from mini digital video tapes were processed using
audio editing software. The sample rate of acoustic record-
ings was 32 or 48 kHz. Single-element recordings were
downsampled by a factor of 3 to allow more detailed visual-
ization of relatively low-frequency sounds, although the
1738 J. Acoust. Soc. Am., Vol. 123, No. 3, March 2008 Zoidis et al.: Humpback calf hydrophone array recordings
original sampling rate data were used to determine the time
delay differences.
Audio data were reviewed in
RAVEN 1.2.1 Charif et al.,
2004 in 30 s segments. Individual analog/digital samples
were plotted and reviewed as a function of time. Detected
pulses were copied and pasted into two different files to al-
low separate analyses of the same data. In the first file, data
were low-pass filtered and decimated to allow higher reso-
lution of low-frequency components. These data were used
to create spectrograms to provide descriptive measurements
of sounds. Spectrograms were calculated with a 1024 fast
Fourier transform FFT, 75% overlap, and a Hamming win-
dow. In the second file, the same original sounds recorded
with the two-element array were band-pass filtered between
100 and 3000 Hz to allow more accurate measurement of
time delays of each sound between the two left and right
channels. Time delays were determined by hand-measuring
the temporal differences between a wave form’s arrival time
at each sensor in milliseconds ms. Time delays and angles
were converted to bearings relative to the sound source as-
suming far-field propagation. Resultant bearings indicated
the angular position of the sound source relative to a plane
parallel to the camera’s optical axis and normal to the line
between the two hydrophones. These bearings are actually
cones or hyperbolic surfaces relative to the plane parallel to
the optical axis of the camera. Video from both divers was
then examined to determine the position of the animals in
the frame at the time of sound production. The relationship
between the time delay and the angle from the plane parallel
to the optical axis of the camera to the sound source consists
of the simple linear formula:
angle = arcsin关共t c/A, 1
where t = time difference between elements s, c = speed of
sound in water m/s, and A =aperture distance between
elements m. Any single-measured angle could represent a
source in any direction on the hyperbolic surface defined by
the array geometry and the time delay differences not nec-
essarily the object in view of the camera, i.e., the sound
source could be directly behind the camera. This was ad-
dressed by conducting both underwater and surface constant
scans for animal presence and locations in relation to the
recording diver. We inferred that the source animal was the
one in front of the diver if no animal occurred behind the
diver and no animals were visually detected on the same
plane as the source animal. In addition, during calf vocaliza-
tions, no other groups were visible underwater or at the sur-
face within 300 m.
Representative spectrograms were selected from clips to
illustrate typical acoustic parameters attributable to calf vo-
calizations Fig. 1. Clips were downsampled by a factor of
8, reducing the sample rate to 6 kHz. Spectrogram illustra-
tions were made with a Hann window, a 512 FFT size, and a
98% overlap. A subsample of vocalizations with loud signal-
to-noise ratios 10 dB, indicating close proximity, and data
supporting the proximal position of the calf relative to other
whales was selected for further analyses. Sounds with low
signal-to-noise ratios, repetitive sounds similar to song,
and/or sounds with more than one animal in the same plane
based on video and field notes were discarded. Selected
sounds were divided into pulsed, amplitude-modulated
AM, and frequency-modulated tonal FM signals. Pulsed
signals had a distinct amplitude onset as opposed to the sinu-
soidal amplitude envelope of a typical AM signal. Duration
and bandwidth, initial and ending AM and FM frequencies,
number of pulses in a pulsed signal, and the first and last
interpulse intervals were measured. It was noted if the inter-
val was constant, increasing, or decreasing with time. It was
not possible to calculate amplitude of sound from the source
animal because we did not have the precise distance mea-
surements necessary to estimate transmission loss with any
degree of certainty.
Statistical analyses were conducted to compare vocaliza-
tions produced by the one calf recorded with the two-element
hydrophone versus the selected subsample of 60 calf-
attributed vocalizations recorded with the single hydrophone.
Three measures of three signal types
AM, FM, and pulsed
were considered: lowest frequency, bandwidth, and duration.
These measures were chosen as they are independent of each
other. A mean value for each whale, measurement type, and
signal type was calculated. Means were used to avoid un-
equal representation of one animal compared to another, as
the number of vocalizations produced by each animal varied
between focal sessions. Means were compared using a mul-
tivariate analysis of variance MANOVA , with the three
dependent measures compared for the two-element hydro-
phone array recordings of one calf in 2006 against the single-
element hydrophone recordings of 21 different calves in
Underwater behavior from the recorded video of all
whale groups was analyzed using a modified behavioral sam-
pling methodology based on Mann 1999. Behavioral state,
individual behaviors, and vocalizations were noted for 30 s
periods that the calf was in view for at least 15 s. Distance
between mother, calf, and diver and depth of animals below
the water surface were estimated in mother-whale body
lengths similar to Glockner and Venus 1983, assuming an
FIG. 1. Spectrograms of typical signal types attributed to a humpback whale
calf based on sounds recorded with the two-element array. Five pulses are
seen between 0.7 and 1.7 s. These are followed by a long tonal or slight
frequency-modulated FM兲兴 signal starting at 2.1 s. Above each spectrogram
is a representation of the signal wave form i.e., the recorded time series of
voltages from the hydrophone shown on the y axis; time on the x axis.
J. Acoust. Soc. Am., Vol. 123, No. 3, March 2008 Zoidis et al.: Humpback calf hydrophone array recordings 1739
average body length of approximately 13 m for a Hawaiian
mother humpback per Spitz et al. 2000. For example, if a
calf was separated from its mother by two mother-body
lengths this separation distance was estimated to be approxi-
mately 26 m; the margin of error was not measured but was
believed to be approximately 2 m based on the standard
deviation and range of measured body lengths of 26 mother
whales per Spitz et al. 2000. The mother was identified
based on its closer consistent contact with the calf and geni-
tal morphology, the latter which was also used to determine
sex of calves True, 1904; Glockner, 1983.
Underwater video recordings of 170 groups containing a
mother-calf humpback were filmed off Maui and Kauai from
January to March for 1 3 months of each of the following
years: 2001, 2002, 2004, 2005, and 2006. A total of
1007 min of videotape was recorded mean= 5.0 min per
group, SD= 4.9, range= 1–30 min. Nonsong vocaliza-
tions were recorded in 110 65% of the 170 groups with a
calf. Of the total 170 calf pods, nonsong vocalizations were
detected in 87% or 34 of 39 lone mother–calf pairs and 68%
or 76 of 111 mother–calf escorts; no calf nonsong vocaliza-
tions were detected among the 20 mother-calf pairs with two
or more escorts. Many vocalizations were of relatively low
amplitude and were not detected until later aural and spectral
analyses of video and acoustic data.
The two-element array system was used off Maui for
one day on 9 March 2006 for a total of 51 min on three
separate mother–calf groups. Quality acoustic data were ob-
tained for one group, a male calf accompanied by a mother
and escort; they were observed and recorded for 38 continu-
ous min of which 18 min was recorded with the two-element
array set up simultaneous with a second underwater video
camera and single hydrophone. The remaining 109 95%
calf groups with nonsong vocalizations were recorded using
the single hydrophone-video camera set up. Nearly all 97%
of these 109 groups and videotape 96% were recorded near
Maui; the remaining 3% were near Kauai. Acoustic data and
videotape were analyzed for the one calf recorded with the
two-element array and for a selected subsample of 28 calves
from 109 groups as described here. All 29 calves consisted of
different individuals based on examination of physical at-
tributes of both the calf and mother e.g., fluke, pectoral fin,
and body pigment patterns, body creases, sex, and/or scar-
ring e.g., Katona et al., 1979; Glockner and Venus, 1983兲兴.
The one vocalizing calf recorded by the two-element array
was male, whereas the 28 calves recorded with the single
hydrophone consisted of 10 males and 18 females. All 29
whales assessed to be mothers based on close association
with the aforementioned calves were sexed via underwater
video data as females.
A. Two-element array recording of one calf
Directional bearings were determined for 21 distinct bio-
logical sound signals from the one male calf based on mea-
sured time delays of recordings between the two hydro-
phones of the two-element array Table I. We analyzed nine
different representative video clips separate time segments
from the 18 min data series of this encounter providing real-
time visual corroboration that the calf was the only animal
present in the area of the recorded sounds. The calf is clearly
visible in the center of all these frames. For example, a signal
identified as a grunt occurred 160.8 s into clip 15 Fig. 2.
The measured time delay between the left and right hydro-
phones was 0.104 ms, corresponding to an angle of 6.14°,
just slightly offset from the plane between the two hydro-
phones. No other animals were behind the calf being videoed
or behind the first diver, verifying that the calf in front of the
hydrophone made the sounds. A different animal behind the
first diver is the only other scenario in which this time delay
difference and resulting acoustic signals could possibly have
been recorded. This was ruled out based on analysis of un-
derwater video taken by the second diver, by constant vessel
observer scans confirming that no other animals were nearby,
TABLE I. Distribution of signal types recorded from the one humpback
whale calf with the two-element array and attributed to 28 humpback whale
calves recorded with the single hydrophone. No significant differences were
found between sounds recorded with the two-element array vs the single
hydrophone for the three signal types based on lowest frequency, bandwidth,
and duration parameters as indicated here. AM= amplitude modulated, and
FM=frequency modulated.
Signal type
n =1
n =28
Total n %
AM 2 12 14 17 F2,1 = 0.1285,
p= 0.8919
FM 4 30 34 42 F2,4 = 0.2483,
p= 0.7914
Pulsed 15 18 33 41 F2,3 = 1.7988,
P= 0.3066
number of
n=21 n=60 n=81
Excludes duplicative sounds recorded by a single hydrophone simultaneous
to the two-element array for the one calf recorded with the two-element
array in 2006.
FIG. 2. Color online Spectrogram of an amplitude-modulated “grunt” sig-
nal produced by the humpback whale calf recorded by the two-element
1740 J. Acoust. Soc. Am., Vol. 123, No. 3, March 2008 Zoidis et al.: Humpback calf hydrophone array recordings
and data indicating that the mother and escort were resting at
deeper water depth and were not within the angle offset
The types and structures of the 21 vocalizations measur-
ably attributed to the same calf via the two-element array
were predominantly pulsed signals 71%, followed by 19%
FM and 10% AM signals Tables IIII. All 21 signals were
relatively short in duration 1 s; mean= 208 ms, SD= 147,
range= 89 664 ms and of predominantly low frequency
Table II. Mean lowest frequency of the 21 signals was
220 Hz SD=391.5, range=10 1464 Hz. Mean highest fre-
quency was 2221 Hz SD= 1861.4, range 3127719 Hz.
Vocalizations had a relatively narrow bandwidth 2004 Hz,
SD= 1891, range= 238 7118 Hz with a mean maximum
frequency of 2.22 kHz range=239 7719 Hz. Table II
shows summary statistics for the AM, FM, and pulsed sig-
nals recorded from this calf. “Grunt” vocalizations were the
most commonly heard signal 90% of 21 from this calf
based on aural analyses Fig. 2.
The calf made a total of four close 1–5 m approaches
to the diver, once during each of four surfacing bouts. During
three approaches, the calf emitted 4—8 repetitive “grunts”
and looked directly at the diver at its closest point of ap-
proach. The group consisting of the mother, calf, and adult
escort remained in the same approximate location, resting
near the shallow 30 m bottom.
Supplemental information providing a detailed descrip-
tion of this encounter, including behaviors associated with
calf vocalizations and types of vocalizations, is available at
the Cetos Research Organization website 2007.
B. Single hydrophone recordings of calves
A subsample of 28 of the 109 calf groups with non-song
vocalizations recorded only with the single hydrophone was
selected for detailed analyses based on quality of videotape
and acoustic signals. These 28 groups yielded a subsample of
60 sound signals considered of reasonable quality and cir-
cumstance to be attributable to a calf using methods similar
to previous reports Zoidis and Green, 2001; Pack et al.,
2005; Zoidis et al., 2005 and data from the two-element
array as follows: 1 The same 21 vocalizations made by the
calf verified with the two-element array were recorded simul-
taneously by the single hydrophone, i.e., the omnidirectional
hydrophone had coincident sounds that were verified sepa-
rately as coming from the calf by the two-element array data.
2 No significant differences were found between the char-
acteristics of three acoustic parameters of selected single-
hydrophone vocalizations and those recorded and linked to
the calf by the two-element array Table II. 3 27 of the 28
calves that produced vocalizations were alone defined as
isolated with no other whales in view within at least 15 m for
at least 15 min and no humpback song sounds recorded. 4
Nonsong vocalizations were detected significantly more fre-
quently when the calf was at or near its closest point of
approach to the single hydrophone 5m facing the diver/
recorder whereas the mother and/or escort were resting in
deeper water 10 m from the diver and calf n = 49, X
=49.0, p=0.002, df =2. 5 The vocalizations had a rela-
tively strong signal-to-noise ratio 10 dB. 6 Two different
calves emitted bubbles concurrent with the time of the vo-
Most 90% of the above 60 signals were short in dura-
tion 1.1 s, mean=559 ms, range=75 ms 2.5 s and of
predominantly low frequency overall mean low frequency
of all 60 was signals= 306 Hz, range= 101710 Hz. FM sig-
nals were most common 50% followed by pulsed 30%
and AM 20% signals Table I. Of the 30 FM signals, eight
were simple upsweeps, six were simple downsweeps, eight
had near-flat frequency contours, and the remaining eight
had inflections in their contours e.g., U-shaped. Nine of the
twelve AM sounds had no strong changes in AM frequency,
two increased, and one had a complex pattern of modulation.
The large single hydrophone AM value of the “highest fre-
quency” Table II is the result of measuring all of the side
bands for the 12 AM sounds. The measured bandwidth of
TABLE II. Summary statistics for the amplitude-modulated AM, frequency-modulated FM, and pulsed signals for a male humpback whale calf recorded
with the two-element T, hydrophone array n = 21 signals, and 60 signals attributed to 28 humpback calves recorded with the single hydrophone S.The
mean value is provided for each measure with the standard deviation in parentheses. AM= amplitude modulated, FM= frequency modulated, Hz= hertz, and
ms n
NA NA 30
NA NA 164
NA NA 384
Measured bandwidth of the AM signals is larger than that of the FM signals, as only the fundamental was measured and harmonics were excluded.
Large AM value of the category highest frequency is the result of measuring all side bands of the 12 AM sounds.
J. Acoust. Soc. Am., Vol. 123, No. 3, March 2008 Zoidis et al.: Humpback calf hydrophone array recordings 1741
TABLE III. Comparison of vocalizations produced by young of large whale species. Age classifications are
taken directly from referenced papers and may have been assessed by non-similar standards. Sample size
provided when presented in literature. AM=amplitude modulated, FM=frequency modulated, Hz=hertz, SD
=standard deviation, s=second, and MSB=mean sound bandwidth.
Species, age classification,
sample size
Type: Bandwidth Hz
MSB, SD, range
duration, SD,
range s
Humpback whale
Megaptera novaeangliae
calf vocalizations linked
with two-element array
2006: n = 1 calf, 21
Pulsed: MSB 2359,
SD 243
FM: MSB 1024,
SD 395
AM: MSB 1305,
SD 182
Pulsed: 0.16,
SD 0.07
FM: 0.25,
SD 0.20
AM: 0.47,
SD 0.28
This study
Overall range: 238–7118 Overall mean:
0.21, SD 0.15,
Range: 0.01–0.66
Humpback calf-attributed
vocalizations recorded
with single hydrophone
2001–2005: n = 28 calves,
60 vocalizations
Pulsed: MSB 2808,
SD 2136
FM: MSB 531,
SD 677
AM: MSB 3519,
SD 2608
Pulsed: 0.38,
SD 0.24
FM: 0.58,
SD 0.50
AM: 0.77,
SD 0.61
This study
Overall range: 140–4000 Overall mean:
Range: 0.08—2.5
Humpback calf-attributed
vocalizations recorded
with single hydrophone
1996–2003: n = 8 calves,
49 vocalizations
Constant rate pulse:
MSB 794,
Increasing or decreasing
rate pulse: MSB 775,
Upswept frequency tone:
MSB 1297,
Sound combination:
MSB 1021,
Median fundamental
frequency 90,
Overall range: 30–3000
Mean: 0.38,
Range: 0.11–0.71
Pack et al., 2005
Adult humpback groups
n =54
Social sounds range:
50–10 000,
dominant frequencies
mostly FM upsweeps
0.25 5
Silber, 1986
Adult male humpbacks
Song range: 20 24000 Range:
Payne and
McVay, 1971;
Helweg et al.,
1992; Au et al.,
2000, 2001, 2005,
2006; Fristrup et al.,
2003; Potter
et al.,2003
Gray whale Eschrichtius
robustus female calf, 1.57
old n=1 calf
240 h of recordings
Type 1a “croak” pulses
Type 1b “pop” pulses
Type 3 “moan”
: 80–2120
Type 4 “grunt”
: 70–5000
Type 1a: 0.039,
SD 0.012
Type 1b: 0.072,
SD 0.027
Type 3: 0.44,
SD 0.20
Type 4: 0.34,
SD 0.090
Wisdom et al.,
North Atlantic right whale
Eubalaena glacialis
female calf n =1 calf, 9
Warble range:
Parks and Tyack,
1742 J. Acoust. Soc. Am., Vol. 123, No. 3, March 2008 Zoidis et al.: Humpback calf hydrophone array recordings
these AM signals is larger than that of the FM signals, par-
tially because only the fundamental was measured and the
harmonics were excluded from the measurement.
We recorded unusual behavioral events when calf-
attributed vocalizations were recorded that to our knowledge
have not been previously reported. A selective representation
of these include the following: Repeated grunt series by three
separate calves that increased in amplitude followed by the
mother joining the calf from depth and “herding” the calf
away from the diver, who was less than 5 m from the calf at
the time of sound production; this type of directed movement
behavior by the mother was not seen when no sounds were
recorded. Two of these calves repeatedly produced grunt
sounds and simultaneously created underwater bubble
streams. One of these calves was recorded for a 3 : 04-min
continuous sequence of grunts, the longest duration of any
year and the farthest 30 m a calf was away from its
mother who was in deeper water and not visible to the diver.
The grunts increased in tempo and coincided with repeated
bubble streams and an underwater “jaw clap.”
Nonsong vocalizations occur in all adult humpback
group compositions on the wintering grounds, including
those with a calf, as documented previously and herein Ty-
ack, 1983; Silber, 1986; Zoidis and Green, 2001; Pack et al.,
2005; Zoidis et al., 2005. For the first time, measured time
delays between array bearings provide measurable evidence
corroborating that a male humpback calf produced 21 non-
song vocalizations as recorded with a nonstatic two-element
array mounted on an underwater video camera. Previously,
vocalizations have been attributed to individual humpback
calves on the wintering grounds based only on observational
evidence and recordings with a single-hydrophone video
camera including the 60 vocalizations from 28 other calves
reported herein兲共Zoidis and Green, 2001; Pack et al., 2005;
Zoidis et al., 2005. Although convincing, the methodology
used in these studies cannot unequivocally rule out that the
sounds did not come from another source/whale that was
nearby or not visible because one omnidirectional hydro-
phone cannot provide directional bearings spatially linking
acoustic data to a source. However, the two-element array
calf recordings combined with similarities in sound charac-
teristics between this calf and other calf-attributed vocaliza-
tions provide further substantiation that both male and fe-
male humpback calves vocalize.
Nonsong vocalizations appear more common among
wintering humpback calf pods than previously reported.
Herein, nonsong vocalizations were recorded in 65% of 170
calf pods. Silber 1986 recorded nonsong social sounds in
only 7% of 14 mother–calf–escort groups and in none of
seven lone mother–calf pairs. Pack et al. 2005 attributed 49
vocalizations to eight humpback calves off Maui the number
of calf pods that did not vocalize was not reported. In addi-
tion, we found nonsong vocalizations more common in lone
mother–calf pairs than among mother–calf–escort groups.
Similarly, Zoidis and Green 2001 reported a significantly
higher vocalization rate 10.9 vocalizations per whale per
hour among 12 mother–calf pairs compared to 50 mother–
calf–escort groups 4.4, 25 surface-active groups of three or
more adults with no calves 4.2, and seven adult dyads
1.7. In contrast, both Silber 1986 and Pack et al. 2005
reported nonsong or calf vocalizations primarily among
mother–calf–escorts. Per Pack et al. 2005, five of eight
calves that vocalized were escorted by a mother and one
escort including one singing escort; the remaining three
groups with such sounds were a mother–calf pair, one
mother–calf with two escorts, and one lone calf the defini-
TABLE III. Continued.
Species, age classification,
sample size
Type: Bandwidth Hz
MSB, SD, range
duration, SD,
range s
Bryde’s whale
Balaenoptera edeni
juvenile n = 1 calf, 233
Discrete pulse range:
Pulsed moan range:
Discrete pulse
range: 0.010,
Pulsed moan
range: 0.5–51
Edds et al.,1993
Bryde’s whale calf n =1
calf, 36 calls
Discrete pulse series
range: 700–900
Discrete pulse
range: 0.025–0.040,
Edds et al.,1993
Mean, MSB, median, SD, and/or range are reported if available. Studies did not always report the same units
and parameters.
Maximum recording equipment frequency was 10 kHz.
Captive animal.
Produced by 1.5 months of age.
Produced at 7 months of age.
1 2 year old animal
10 was indicated simply as “duration” in Edds et al. 1993 and appears to be a range
compared to other numbers presented in the original document table.
Recorded with an omnidirectional hydrophone on two occasions when only first-year free-ranging calves were
present at the surface, whereas an adult companion was diving. The discrete pulses were loudest when a calf
was close to the hydrophone and thus may have been produced by a calf Edds et al., 1993. Discrete pulses
were recorded only near these individual calves during opportunistic studies of free-ranging Bryde’s whale
J. Acoust. Soc. Am., Vol. 123, No. 3, March 2008 Zoidis et al.: Humpback calf hydrophone array recordings 1743
tion, i.e., duration of how long a calf was “alone” was not
indicated. Five of these calves were males and three were
females Pack et al., 2005. In comparison, we attributed
vocalizations to 11 male and 18 female calves.
Calf vocalizations recorded with the two-element array
were simple in structure and limited in repertoire with short
duration and interpulse interval, and predominantly low fre-
quency and relatively narrow bandwidth. These characteris-
tics were not significantly different from other vocalizations
attributed to humpback calves in this study and are similar to
acoustic characteristics reported in earlier reports of calf vo-
calizations Zoidis and Green, 2001; Pack et al., 2005; Zoi-
dis et al., 2005兲共Table III. Calves appear to produce se-
quences of the same sound in some instances. Repeated
grunt bouts were made by the two-element-array recorded
calf and were also recorded near calves by the single hydro-
phone. Similarly, Pack et al. 2005 reported that four calves
produced sound sequences at a mean interval of 4.4 s, the
spectral characteristics of which were similar to the grunt
sounds we recorded Fig. 2. In addition, vocalizations were
documented simultaneous to bubble emissions from the
blowhole for both the two-element array recorded calf as
well as calves recorded with the single hydrophone herein
and in Pack et al. 2005 Figs. 1 and 2.
Pack et al. 2005 found that calf-attributed vocaliza-
tions were statistically similar to “noncalf social sounds”
terminology from Pack et al. 2005 but were significantly
different from adult song units; the former were noted to
have a narrower frequency range and shorter duration Table
III. Our results for calf vocalizations based on both the two-
element array and single hydrophone recordings generally
corroborate these findings, as do earlier reports that song is
more complex than nonsong adult and calf vocalizations
Silber, 1986; Zoidis and Green, 2001; Zoidis et al., 2005.
In addition, pulsed signals were frequent among calves com-
pared to the known repertoire of pulsed sounds produced by
adult humpbacks in Hawaii e.g., Payne and McVay, 1971;
Darling, 1983; Payne, 1983; Silber, 1986; Helweg et al.,
Au et al., 2000. However, the most common type of
signal recorded by the single hydrophone was FM signals, as
found by Silber 1986 for groups of three or more adults off
Maui Table III. Most AM signals we recorded near calves
had no strong evidence of changes in AM frequency. In con-
trast, social sounds of surface-active adult humpback groups
typically exhibit considerable modulation in the AM fre-
quency, producing the sensation of a frequency sweep Sil-
ber, 1986.
Underwater video documenting behaviors and surround-
ings concurrent with two-element array recordings were im-
portant in providing empirical real-time evidence that a calf
produced vocalizations. This approach allows an animal to
be monitored visually and acoustically i.e., it remains in
view for extended periods, so that underwater behaviors can
be continuously recorded concurrently with vocalizations.
Previous studies e.g., Tyack, 1981, 1983; Darling, 1983; Sil-
ber, 1986 recorded nonsong sounds among adult humpback
whales by deploying a single hydrophone from a small ves-
sel. More recently, Dunlop et al. 2005, 2006, and Dunlop
and Noad 2007 recorded nonsong vocalizations in Australia
remotely from shore using a stationary array. No directional
data linking vocalizations to individuals were presented in
these previous studies.
The function and biological significance of calf vocal-
izations are unknown. Several potential hypotheses are pro-
posed. Some types of calf vocalizations may elicit the moth-
ers approach. In most cases, a calf closely 5to10m
approached the diver either silently or with nonsong vocal-
izations during a surfacing bout, with no reaction from the
mother. However, when on three occasions a calf emitted
repeated grunt vocalizations, with increasing incidence and
amplitude, twice with bubbles and once with an accompany-
ing jaw clap, the mother surfaced quickly, approached, and
seemingly intentionally “herded” the calf directly away. Cer-
tain sounds e.g., FM signals, repetitive grunts, particularly
those that increase in amplitude and/or bubble streams may
function as either isolation or “alarm” calls by the calf to
alert and/or call the mother. Alarm or isolation calls occur
among mother-young groups of other mammalian species in-
cluding dolphins reviewed in Tyack, 2000, bats Balcombe,
1990, and primates Robinson, 1982. The calf may also
produce vocalizations when encountering a novel stimulus
i.e., a close encounter with a diver or boat, or as unidirec-
tional contact communication from the calf to the mother
i.e., where only one individual recognizes the call of the
other and not visa versa Torianni et al., 2006兲兴. Documen-
tation is lacking as to whether humpback mothers or other
adults use sound to communicate with calves. To date, the
published evidence has not shown this.
A few studies have been able to individually link vocal-
izations to young of other baleen whale species including
gray Wisdom et al., 2001, northern right Parks and Tyack,
2005; Parks and Clark, 2007, and Bryde’s whales Edds et
al., 1993; however, some of these studies have involved
captive animals and may not be representative of free-
ranging animals Table III. Although the vocalizations them-
selves are quite different between species and are limited to a
few individuals, their overall characteristics are generally
similar to humpback calf-attributed vocalizations in terms of
simplicity, limited repertoire, short duration, and predomi-
nantly low and narrowband frequency, when compared to
adults of the same species Edds et al., 1993; Wisdom et al.,
2001; Parks and Tyack, 2005; Parks and Clark, 2007兲共Table
III. A captive juvenile Bryde’s whale produced primarily
pulsed moans with amplitude and frequency modulation, and
on two occasions, free-ranging isolated Bryde’s calves were
linked with series of 4–11 discrete pulse calls Edds et al.,
1993. Series of pulsed vocalizations i.e., pulse trains were
also commonly produced by a captive gray whale calf Wis-
dom et al., 2001 as well as an entrapped juvenile humpback
Beamish, 1979 and humpback calves reported herein and
by Pack et al. 2005 Table III. Published individual sound
confirmation of Northern right whale calves is limited to one
free-ranging female based on bearing data collected with an
acoustic array on the feeding grounds Parks and Tyack,
2005; Parks and Clark, 2007. This calf produced stuttered
“screamlike” calls interrupted by many pauses when alone at
the surface as the other adults in the group dove. The calls
1744 J. Acoust. Soc. Am., Vol. 123, No. 3, March 2008 Zoidis et al.: Humpback calf hydrophone array recordings
were generally of higher pitch and often longer in duration
than adult female “screams” used to initiate surface-active
adult groups Parks and Tyack, 2005.
The biological significance of vocalizations produced by
humpback calves and how it may change depending on so-
cial structure, environmental cues, ontogeny, and behavior,
as well as whether mothers vocalize, remains to be further
investigated. Circumstances of calf-attributed vocalizations
recorded with a single hydrophone provide strong indication
that the calf is most likely the sound source rather than the
mother, including in lone mother–calf pairs. Compelling ob-
servational data include vocalizations recorded coincident
with bubble emissions by humpback calves during both two-
element and single hydrophone recordings, similar to hump-
back whale calves and a juvenile reported elsewhere
Beamish, 1979; Zoidis and Green, 2001; Pack et al., 2005;
Zoidis et al., 2005 A captive juvenile Bryde’s whale emitted
bubbles only when vocalizing, throughout the vocalizations,
and only from the right blowhole Edds et al., 1993. Dol-
phins sometimes emit bubbles simultaneous to sound pro-
duction Dahlheim and Awbrey, 1982; McCowan, 1995; Mc-
Cowan and Reiss, 1995; Dudzinski, 1996; Herzing, 1996;
Killebrew et al., 1996, 2001, although this relationship is
not consistent Caldwell et al., 1990; Fripp, 2005. However,
it cannot be ruled out that some sounds recorded by the
single hydrophone were produced by the mother without cor-
roboration from directional acoustic data. Northern right
whale mothers vocalize to their calves when they become
separated, presumably to reunite the two Parks and Clark,
2007. Similar contact calls may occur between humpback
mothers and calves but have not yet been recorded or iden-
tified, possibly due to low-amplitude source levels that are
difficult to detect except at close range. The relatively low
amplitude of calf vocalizations we recorded may be why
calves have only recently been reported to vocalize Zoidis
and Green, 2001.
Further analyses of the acoustic characteristics and be-
havioral context of calf vocalizations are underway, includ-
ing their role as a potential indicator of stress, with implica-
tions for management concerns in areas with elevated
anthropogenic activity and underwater noise such as Hawaii.
The authors thank Randy Bates, Charles Bishop, Dan
DenDanto, M. Green, Carol Hart, Thea Jenson, Terry Mc-
Cabe, Don Moses, Dan Shapiro, Ethan Silva, Jessica Shar-
man, J. Pantukhoff, and Norbert Wu for their assistance and
support with field portions of this project. They thank Pete
Gehring, Thomas F. Norris, Shannon Rankin, Carol Spencer,
P. Stevick, and Jenelle Black for reviewing this manuscript
and/or for their editorial or technical input. They thank all
our donors and patrons that have funded this work so that
this publication was possible. They are also grateful to E. M.
Blair, J. Dennis, S. Katona, D. Kearney, P. Tadd, A. Waldron,
and A. Wright for their support and encouragement over the
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1746 J. Acoust. Soc. Am., Vol. 123, No. 3, March 2008 Zoidis et al.: Humpback calf hydrophone array recordings
... This is especially true for comparisons of calling behavior across varying group compositions. Studies have varied historically in their scope, with some focused solely on a single group type, like mother-calf pairs (Zoidis et al., 2008;Indeck et al., 2020), and others that have drawn comparisons across groups (Palanca, 2021dissertation, Seger, 2016. Older studies that compared signaling across different groups lacked today's technology (e.g., instrumented tags), which allows for more nuanced and robust long-term data collection on individual groups (Silber, 1986). ...
... Interest in the study of humpback whale calls has grown globally in recent years with research conducted in regions such as Australia (Dunlop et al., 2007;Rekdahl et al., 2013;Rekdahl et al., 2015;Dunlop, 2016;Dunlop, 2017;Cusano et al., 2020;Indeck et al., 2020;Recalde-Salas et al., 2020;Cusano et al., 2021), North America (Zoidis et al., 2008;Stimpert et al., 2011;Epp et al., 2021a;Fournet et al., 2015;Fournet M. et al., 2018), South America (Simão and Moreira, 2005;Oña et al., 2019), and Africa (Rekdahl et al., 2017). However, comparatively little work has been conducted to compare calling behavior across different group compositions using long-term datasets. ...
... To an extent, the minimum frequency of calls in mysticete whales is limited by animal size (May-Collado et al., 2007;Martin et al., 2017), with smaller animals possibly being incapable of producing the lowest frequency calls. It is possible that a balance between calf calls, which are generally produced at higher frequencies than those of adults (Zoidis et al., 2008;Indeck et al., 2020), and calls from the adults in these groups, contributed to the frequency values observed Frequency measurements were relatively consistent with expected patterns, which was also true for observed call durations. High arousal during high intensity contexts (i.e., competitive groups) is frequently associated with longer duration calls (Lemasson et al., 2012). ...
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Humpback whales (Megaptera novaeangliae) are exceptionally vocal among baleen whale species. While extensive research has been conducted on humpback whale songs, gaps remain in our understanding of other forms of communication, particularly non-song calls. Here, we compare the spectral features and temporal parameters of non-song calls recorded from Acousonde tagged humpback whales in three commonly observed group types in the breeding grounds: adult dyads (N = 3), singly escorted mother-calf pairs (N = 4), and competitive groups (N = 4). Recordings were collected off Maui, Hawai’i during the winter breeding seasons of 2019–2021. Individual calls were identified based on visual and aural inspection of spectrograms using Raven Pro 1.6 software, with a total of 842 calls isolated from 47.6 h of acoustic recordings. Competitive groups produced the most calls (N = 358); however, after adjusting for the differences in recording hours and the number of individuals, the call rate (calls/hour/whale) was not significantly different between group compositions. The temporal parameters and frequency measures of calls did not vary significantly across the groups. However, interesting patterns of calling behavior were observed (e.g., competitive groups had the shortest inter-call intervals and the highest frequency calls, and escorted mother-calf pairs had the longest inter-call intervals) and it is possible the lack of statistical significance could be attributed to the small sample size of tag deployments. This study provides new insights into humpback whale vocal communication behavior in the Hawaiian Islands breeding grounds.
... Humpback whales are baleen whales known for their complex, highly structured, and organized songs produced by males in breeding areas (Payne & McVay, 1971) but they also generate social calls. Humpback whales' social calls have been the subject of several studies, both in feeding or breeding grounds, as well as on migration routes (D 'Vincent, Nilson & Hanna, 1985;Silber, 1986;Cerchio & Dahlheim, 2001;Dunlop et al., 2007;Dunlop, Cato & Noad, 2008;Zoidis et al., 2008;Stimpert, 2010;Stimpert et al., 2011;Rekdahl et al., 2013;Fournet, Szabo & Mellinger, 2015;Rekdahl et al., 2017;Indeck et al., 2021). Distinct acoustic units of vocalization or "call types" were generally defined either using an automatic clustering method based of several acoustic parameters (Stimpert, 2010;Stimpert et al., 2011;Fournet, Szabo & Mellinger, 2015) or an aural-visual classification (Dunlop et al., 2007;Dunlop, Cato & Noad, 2008;Zoidis et al., 2008;Rekdahl et al., 2013Rekdahl et al., , 2017Fournet, Szabo & Mellinger, 2015;Fournet et al., 2018;Indeck et al., 2021) validated using a supervised automatic classification (e.g., discriminant function analysis-DFA, Classification and Regression Tree-CART, or random forest-RF) or not. ...
... Humpback whales' social calls have been the subject of several studies, both in feeding or breeding grounds, as well as on migration routes (D 'Vincent, Nilson & Hanna, 1985;Silber, 1986;Cerchio & Dahlheim, 2001;Dunlop et al., 2007;Dunlop, Cato & Noad, 2008;Zoidis et al., 2008;Stimpert, 2010;Stimpert et al., 2011;Rekdahl et al., 2013;Fournet, Szabo & Mellinger, 2015;Rekdahl et al., 2017;Indeck et al., 2021). Distinct acoustic units of vocalization or "call types" were generally defined either using an automatic clustering method based of several acoustic parameters (Stimpert, 2010;Stimpert et al., 2011;Fournet, Szabo & Mellinger, 2015) or an aural-visual classification (Dunlop et al., 2007;Dunlop, Cato & Noad, 2008;Zoidis et al., 2008;Rekdahl et al., 2013Rekdahl et al., , 2017Fournet, Szabo & Mellinger, 2015;Fournet et al., 2018;Indeck et al., 2021) validated using a supervised automatic classification (e.g., discriminant function analysis-DFA, Classification and Regression Tree-CART, or random forest-RF) or not. The recordings were obtained using moored or towed hydrophones (Dunlop et al., 2007;Dunlop, Cato & Noad, 2008;Stimpert, 2010;Rekdahl et al., 2013Rekdahl et al., , 2017Fournet, Szabo & Mellinger, 2015;Fournet et al., 2018;, using hydrophone carried by divers (Zoidis et al., 2008), or using animal borne tags (Stimpert, 2010;Stimpert et al., 2011;Indeck et al., 2021). ...
... Distinct acoustic units of vocalization or "call types" were generally defined either using an automatic clustering method based of several acoustic parameters (Stimpert, 2010;Stimpert et al., 2011;Fournet, Szabo & Mellinger, 2015) or an aural-visual classification (Dunlop et al., 2007;Dunlop, Cato & Noad, 2008;Zoidis et al., 2008;Rekdahl et al., 2013Rekdahl et al., , 2017Fournet, Szabo & Mellinger, 2015;Fournet et al., 2018;Indeck et al., 2021) validated using a supervised automatic classification (e.g., discriminant function analysis-DFA, Classification and Regression Tree-CART, or random forest-RF) or not. The recordings were obtained using moored or towed hydrophones (Dunlop et al., 2007;Dunlop, Cato & Noad, 2008;Stimpert, 2010;Rekdahl et al., 2013Rekdahl et al., , 2017Fournet, Szabo & Mellinger, 2015;Fournet et al., 2018;, using hydrophone carried by divers (Zoidis et al., 2008), or using animal borne tags (Stimpert, 2010;Stimpert et al., 2011;Indeck et al., 2021). ...
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Humpback whales ( Megaptera novaeangliae ) use vocalizations during diverse social interactions or activities such as foraging or mating. Unlike songs produced only by males, social calls are produced by all types of individuals (adult males and females, juveniles and calves). Several studies have described social calls in the humpback whale’s breeding and the feeding grounds and from different geographic areas. We aimed to investigate for the first time the vocal repertoire of humpback whale mother-calf groups during the breeding season off Sainte Marie island, Madagascar, South Western Indian Ocean using data collected in 2013, 2014, 2016, and 2017. We recorded social calls using Acousonde tags deployed on the mother or the calf in mother-calf groups. A total of 21 deployments were analyzed. We visually and aurally identified 30 social call types and classified them into five categories: low, medium, high-frequency sounds, amplitude-modulated sounds, and pulsed sounds. The aural-visual classifications have been validated using random forest (RF) analyses. Low-frequency sounds constituted 46% of all social calls, mid-frequency 35%, and high frequency 10%. Amplitude-modulated sounds constituted 8% of all vocalizations, and pulsed sounds constituted 1%. While some social call types seemed specific to our study area, others presented similarities with social calls described in other geographic areas, on breeding and foraging grounds, and during migrating routes. Among the call types described in this study, nine call types were also found in humpback whale songs recorded in the same region. The 30 call types highlight the diversity of the social calls recorded in mother-calf groups and thus the importance of acoustic interactions in the relationships between the mother and her calf and between the mother-calf pair and escorts.
... Studying the developmental ontogeny of song within individual males would require directed effort to record vocal production by juvenile males at various stages during their growth and maturation, an undertaking which has not been attempted, to our knowledge. Studies of calves with their mothers on the breeding grounds have revealed the production of non-song sounds by calves (Zoidis et al. 2008;Saloma 2018), but documentation of song production and song structure of sexually immature males is lacking. Such studies would reveal insights into how individual males develop and learn their songs. ...
It has been fifty years since Payne and McVay’s seminal publication on the strange and beautiful sounds of the humpback whaleHumpback whale (Megaptera novaeangliaeMegaptera novaeangliae), the study which inspired decades of research into their complex, underwater acoustic world. In the subsequent five decades, there probably have been more research projects and publications on humpback whaleHumpback whale song than on the vocal behavior of any other baleen whale. What makes humpback song so unique? What have we learned? What questions remain? With this chapter, we explore these questions with an eye toward the overarching theme of studies that address proximate mechanisms (the “how do humpback whalesHumpback whaledo this?” questions) versus those that inquire about ultimateProximate vs ultimate causes (the “why do humpback whalesHumpback whaledo this?” questions). We draw a distinction between studies that focus on singing behavior, versus those that use song as a proxy to investigate other biological processes. We take the reader through a historical review of the literature, ending with a series of observations about the unanswered questions intended to provoke new ideas and new lines of inquiry. Through this exploration, we hope to synthesize a global body of research to identify common themes and probe the lingering gaps in our understandings of humpback whaleHumpback whale song.
... Zoidis et al. [128] Southwest Pacific Australian east coast Behavioural observations and underwater recordings ...
Plans for large-scale economic developments in the Indian Ocean, including increased shipping, oil and gas exploration and offshore mining, have resulted in concerns about potential impacts on cetaceans. Two species of particular interest are the resident, coastal Indian Ocean humpback dolphin Sousa plumbea and the migratory humpback whale Megaptera novaeangliae. As the two species belong to different hearing groups (high-frequency odontocetes vs low-frequency mysticetes), we review the available literature on their differing hearing mechanisms (physiology), specialities and sensitivities here as there is a lack of data available for these two species in the Indian Ocean region. The reviewed information included audiogram data, species-specific frequencies and sensitivity ranges, ear morphology and adaptations for hearing in their respective groups where available. For odontocetes, most information stems from animals under human care, while for mysticetes bioacoustic measurements, like audiograms, are more difficult to access, resulting in a lack of data on hearing for M. novaeangliae. Our review highlights an absence of baselines upon which to measure future impacts from anthropogenic developments in the Indian Ocean and we suggest future work to address this. Our work is not only timely in view of the planned anthropogenic developments in the Indian Ocean, but also has wider implications in the global context as cumulative impacts on cetaceans grow due to increased international demand for resources and associated Ocean Economy developments.
... Songs are a largely seasonal reproductive display produced prolifically on the breeding grounds, as well as during migration, and on feeding grounds pre-and post-migration (Edds-Walton, 1997; Dunlop and Noad, 2016;Gridley et al., 2018;Kowarski et al., 2021;Ross-Marsh et al., 2021). Song notes can range in frequency from approximately 20 Hz to above 24 kHz (Au et al., 2006;Stimpert et al., 2007;Zoidis et al., 2008;Cholewiak et al., 2013). ...
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Little is known of the movements and seasonal occurrence of humpback whales (Megaptera novaeangliae) of South Africa and the Antarctic, populations once brought to near extinction by historic commercial whaling. We investigated the seasonal occurrence and diel-vocalizing pattern of humpback whale songs off the west coast of South Africa (migration route and opportunistic feeding ground) and the Maud Rise, Antarctica (feeding ground), using passive acoustic monitoring data collected between early 2014 and early 2017. Data were collected using acoustic autonomous recorders deployed 200-300 m below the sea surface in waters 855, 1,118 and 4,400 m deep. Acoustic data were manually analyzed for humpback whale vocalizations. While non-song calls were never identified, humpback whale songs were detected from June through December in South African waters, with a peak in percentage of acoustic occurrence around September/October in the austral spring. In Antarctic waters, songs were detected from March through May and in July (with a peak occurrence in April) where acoustic occurrence of humpback whales was negatively correlated to distance to the sea ice extent. Humpback whales were more vocally active at night than in the day at all recording sites. Detection range modelling indicates that humpback whale vocalizations could be detected as far as 18 and 45 km from recorders in South African and Antarctic waters, respectively. This study provides a multi-year description of the offshore acoustic occurrence of humpback whales off the west coast of South Africa and Maud Rise, Antarctica, regions that should continue to be monitored to understand these recovering populations.
... Therefore, contact calling is likely fundamental for calf survival. Humpback whale adult female-calf calls are commonly heard on the breeding grounds and during migration (Dunlop et al., 2008;Videsen et al., 2017;Zoidis et al., 2008). They exhibit considerable differences in their acoustic parameters between age classes and the variety of call types produced suggests that they may serve several potential functions, including as contact, distress, and/or nursing calls. ...
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Acoustic communication is important for animals with dependent young, particularly when they are spatially separated. Maternal humpback whales (Megaptera novaeangliae) use acoustic calling to help minimize the risk of separation from their young calves during migration. These pairs also use acoustic crypsis to minimize detection by males. How they balance a restricted active space with the need to maintain acoustic contact during periods of separation is not yet understood. Here, we analyzed movement metrics of tagged adult female-calf pairs during migration to identify two behavioral states, "resting/milling" and "travelling." When travelling, these pairs dived synchronously and exhibited little to no spatial separation. Alternatively, adult females had significantly longer dive durations (p < .01) when resting, and while they spent prolonged times at depth, calves would surface several times independently. This demonstrated that these pairs are frequently separated during periods of rest. We then determined whether the call rates and acoustic levels of these pairs increased with more frequent separation, finding that both adult females and calves significantly increased their call rates, but not levels, when resting. We also found that adult female-calf pairs have a restricted active space, with less than 15% of calls estimated to be detectable beyond 2 km. However, as with call level, detection distance did not differ significantly between the two behavioral states. In summary, adult female-calf pairs maintain successful communication during periods of separation by calling more frequently rather than by producing louder calls. This strategy aids in maintaining acoustic contact while simultaneously limiting detectability by conspecifics.
... Humpback whales produce a variety of vocalizations (e.g., Stimpert et al., 2007Stimpert et al., , 2011Au and Hastings, 2008). So-called "social sounds" are produced by all ages and sexes and occur on the feeding grounds, along migratory routes, and on the breeding grounds (Silber, 1986;Dunlop et al., 2008;Zoidis et al., 2008;Darling, 2015). In contrast, "song, " known by sailors for centuries, but first formally described by Payne and McVay (1971), is a complex acoustic display produced by mature male humpback whales and some non-calf subadults (Herman et al., 2013). ...
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Passive acoustic monitoring (PAM) with autonomous bottom-moored recorders is widely used to study cetacean occurrence, distribution and behaviors, as it is less affected by factors that limit other observation methods (e.g., vessel, land and aerial-based surveys) such as inclement weather, sighting conditions, or remoteness of study sites. During the winter months in Hawai‘i, humpback whale male song chorusing becomes the predominant contributor to the local soundscape and previous studies showed a strong seasonal pattern, suggesting a correlation with relative whale abundance. However, the relationship between chorusing levels and abundance, including non-singing whales, is still poorly understood. To investigate how accurately acoustic monitoring of singing humpback whales tracks their abundance, and therefore is a viable tool for studying whale ecology and population trends, we collected long-term PAM data from three bottom-moored Ecological Acoustic Recorders off west Maui, Hawaii during the winter and spring months of 2016–2021. We calculated daily medians of root-mean-square sound pressure levels (RMS SPL) of the low frequency acoustic energy (0–1.5 kHz) as a measure of cumulative chorusing intensity. In addition, between December and April we conducted a total of 26 vessel-based line-transect surveys during the 2018/19 through 2020/21 seasons and weekly visual surveys ( n = 74) from a land-based station between 2016 and 2020, in which the location of sighted whale pods was determined with a theodolite. Combining the visual and acoustic data, we found a strong positive second-order polynomial correlation between SPLs and abundance (land: 0.72 ≤ R ² ≤ 0.75, vessel: 0.81 ≤ R ² ≤ 0.85 for three different PAM locations; Generalized Linear Model: p land ≪ 0.001, p vessel ≪ 0.001) that was independent from recording location ( p land = 0.23, p vessel = 0.9880). Our findings demonstrate that PAM is a relatively low-cost, robust complement and alternative for studying and monitoring humpback whales in their breeding grounds that is able to capture small-scale fluctuations during the season and can inform managers about population trends in a timely manner. It also has the potential to be adapted for use in other regions that have previously presented challenges due to their remoteness or other limitations for conducting traditional surveys.
... Males produce stereotyped songs during the breeding season (Payne and McVay, 1971), and all humpback whales produce a large repertoire of social calls. These calls are produced by all age and sex classes Zoidis et al., 2008;Indeck et al., 2021), and in all habitats [e.g., breeding grounds (Tyack and Whitehead, 1983;Silber, 1986), feeding grounds (Jurasz and Jurasz, 1979;D'Vincent et al., 1985;Thompson et al., 1986;Stimpert et al., 2007Stimpert et al., , 2011Parks et al., 2014;Fournet et al., 2015), and on migration (Dunlop et al., 2007(Dunlop et al., , 2008Cusano et al., 2020)]. The number of calls within the repertoire is variable, depending on the population, habitat area, and behavioral context (Dunlop et al., 2007;Stimpert et al., 2008;Fournet et al., 2015;Rekdahl et al., 2017;Cusano et al., 2020). ...
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Intraspecific conflict can be costly; therefore, many species engage in ritualized contests composed of several stages. Each stage is typically characterized by different levels of aggression, arousal, and physical conflict. During these different levels of “intensity,” animals benefit from communicating potential information related to features such as resource holding potential, relative fighting ability, level of aggression, intent (i.e., fight or flight), and whether or not the competitor currently holds the resource (e.g., a receptive female). This information may be conveyed using both visual displays and a complex acoustic repertoire containing fixed (e.g., age, sex, and body size) and flexible information (e.g., motivation or arousal). Calls that contain fixed information are generally considered “discrete” or stereotyped, while calls that convey flexible information are more “graded,” existing along an acoustic continuum. The use of displays and calls, and the potential information they convey, is likely dependent on factors like intensity level. The breeding system of humpback whales (Megaptera novaeangliae) involves intense male competition for access to a relatively limited number of breeding females (the resource). Here, we investigated the behavior and acoustic repertoire of competitive groups of humpback whales to determine if an increase in intensity level of the group was correlated with an increase in the complexity of the vocal repertoire. We categorized the behavior of humpback whales in competitive groups into three mutually exclusive stages from low to high intensity. While discrete calls were infrequent compared to graded calls overall, their use was highest in “low” and “moderate” intensity groups, which may indicate that this stage of contest is important for assessing the relative resource holding potential of competitors. In contrast, visual displays, call rates, and the use of graded call types, were highest during “high intensity” competitive groups. This suggests that flexible information may be more important in “high intensity” levels as males continue to assess the motivation and intent of competitors while actively engaged in costly conflict. We have shown that the relatively complex social call repertoire and visual displays of humpback whales in competitive groups likely functions to mediate frequently changing within-group relationships.
For humpback whales, the mother–calf pair is the only stable social unit with calves following their mother after birth and staying in close proximity. This following strategy ensures the maintenance of such close proximity between the mother and her calf, with calves benefiting from maternal protection and care. Using multi-sensor tags, we recorded the diving behavior of calves at three different age-classes (C1, C2, C3) to assess how calves developed in their natural environment at an early stage of their life. From 29 deployments on calves, we extracted the diving metrics from two C1 neonate calves, eight C2 calves, and 19 C3 calves, and we found that some diving metrics (dive duration, time at bottom, maximal depth, or maximal dive duration) differed among calves’ age-classes. On 23 tagged mothers, we analyzed if their diving profiles also varied depending on calf’s age-class. We showed that only two dive metrics of mothers varied with the age of their own calves (time spent at the bottom, and time interval between dives), but all others were not reliant on the calf’s age. Simultaneous deployments on seven mother–calf pairs in 2016 and 2017 revealed highly synchronized dives, with mothers leading the diving pattern. This work represents an extensive study investigating the diving behavior in humpback whale mother–calf pairs on their breeding ground.
Humpback whalesHumpback whale(Megaptera novaeangliae)Megaptera novaeangliae occur in all major oceans. Given this worldwide distribution, and since they tend to migrate along coastlines, they are one of the best known of the baleen whalesBaleen whale. Humpbacks are relatively easy to find and easy to observe. This, along with their surface behaviorsBehavior and attraction to vessels, makes them popular with whale-watching businesses. In the scientific world, their songSong and behaviorsBehavior have been studied since the 1970s, producing hundreds of scientific papers. Despite this, there are still many unsolved mysteries. Why do humpbacks sing (Chaps. 8 and 11), how do they locate their prey (Chap. 5), and how do they navigate when migrating (Chap. 4)? In this chapter, we focus on the mysteries of their social communicationCommunication. Communication and social complexitiesSocial complexity often go hand in hand. Animals with more complex social structuresSocial structure tend to have more complex vocal repertoiresVocal repertoire, perhaps peaking, with humans. Within the baleen whalesBaleen whale, humpback whalesHumpback whale are considered an exception. Present knowledge indicates that humpbacks have a relatively complex acoustic repertoireAcoustic repertoire but work on their breedingBreedingsocial systemSocial system has considered them to be socially simple. Animals regarded as having a simple social structureSocial structure tend to have small group sizes and a lack of repeat associations between individuals over time. Humpback whalesHumpback whale meet this criteria in that they form temporary associations between a small number of individuals, and these associations are not repeated over time, leading to the conclusion that their social structureSocial structureis simple and individually basedIndividually-based. Why then do humpbacks have what could be considered a complex acoustic repertoireAcoustic repertoire? Is the conclusion that they possess a simple social structureSocial structure supported by best available scientific evidence? This chapter illustrates that humpbacks may in fact have a complex social structureSocial structure, with complexity defined differently than traditional definitions of complexity (number in a group, number of repeat associations). Rather than forming large permanent groups with repeated interactions between individuals, humpback whalesHumpback whale during the breedingBreeding season form networks that encompass multiple groups. These groups are frequently changing membership, and animals are constantly moving into, and out of this network. Whales must therefore continuously assess, and respond to, a changing social environment. Given that humpbacks likely rely on acoustic communicationCommunication to manage these interactions, this added layer of social complexitySocial complexity may go toward explaining their large and varied vocal repertoireVocal repertoire. Perhaps communicative and social complexitiesSocial complexity do go hand in hand for the humpback whaleHumpback whale.
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More than 20 years have elapsed since the first detailed descriptions of humpback whale song (Payne and McVay, 1971; Winn, Perkins and Poulter, 1971) and despite considerable attention, the function of song remains elusive. In this paper, we review the literature on humpback whale song and describe general methods used to collect data on free-ranging whales. Then, we present the results of three current studies that have used different methods to shed light on the function of whale song.
Behavioral scientists have developed methods for sampling behavior in order to reduce observational biases and to facilitate comparisons between studies. A review of 74 cetacean behavioral field studies published from 1989 to 1995 in Marine Mammal Science and The Canadian Journal of Zoology suggests that cetacean researchers have not made optimal use of available methodology. The survey revealed that a large proportion of studies did not use reliable sampling methods. Ad libitum sampling was used most often (59%). When anecdotal studies were excluded, 45% of 53 behavioral studies used ad libitum as the predominant method. Other sampling methods were continuous, one-zero, incident, point, sequence, or scan sampling. Recommendations for sampling methods are made, depending on identifiability of animals, group sizes, dive durations, and change in group membership.
Every year a large number of baleen whales are entrapped in ice and in fishermen’s nets. Many escape on their own. Others die.
Among the large baleen whales, humpbacks are notable for the variety of different white and black patterns and slight morphological differences which can be observed between individuals (Lillie, 1915; Matthews, 1937; Pike, 1953; Schevill and Backus, 1960). Observations in the field and inspection of photographs suggest that variations in the shape of the dorsal fin or in the disposition of body scars can sometimes be used to identify individual humpback whales. It is primarily the pattern on the underside of the flukes which appears to us to provide the most positive discrimination between individual humpback whales. This pattern varies from nearly all white to nearly all black, but characteristically contains a variety of black or white patches, lines or streaks.