Intra- and intergroup vocal behavior in resident killer whales, Orcinus orca
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Intra- and intergroup vocal behavior in resident killer whales,
Orcinus orca
Brigitte M. Weißa兲
Department of Behavioural Biology, University of Vienna, A-1090 Vienna, Austria
Helena Symonds and Paul Spong
OrcaLab, P.O. Box 258, Alert Bay, B.C., V0N 1A0, Canada
Friedrich Ladichb兲
Department of Behavioural Biology, University of Vienna, A-1090 Vienna, Austria
共Received 13 June 2007; revised 21 September 2007; accepted 25 September 2007兲
Vocal communication within and between groups of individuals has been described extensively in
birds and terrestrial mammals, however, little is known about how cetaceans utilize their sounds in
their natural environment. Resident killer whales, Orcinus orca, live in highly stable matrilines and
exhibit group-specific vocal dialects. Single call types cannot exclusively be associated with
particular behaviors and calls are thought to function in group identification and intragroup
communication. In the present study call usage of three closely related matrilines of the Northern
resident community was compared in various intra- and intergroup contexts. In two out of the three
matrilines significant changes in vocal behavior depending both on the presence and identity of
accompanying whales were found. Most evidently, family-specific call subtypes, as well as aberrant
and variable calls, were emitted at higher rates, whereas “low arousal” call types were used less in
the presence of matrilines from different pods, subclans, or clans. Ways in which the observed
changes may function both in intra- and intergroup communication.
© 2007 Acoustical Society of America. 关DOI: 10.1121/1.2799907兴
PACS number共s兲: 43.80.Ka 关WWA兴 Pages: 3710–3716
I. INTRODUCTION and reflect genetic relatedness 共Barrett-Lennard 2000兲.
Closely related matrilines are referred to as “pods” 共Bigg
Vocal communication within and between groups of in-
et al., 1990兲 and share most or all of their call repertoire.
dividuals has been described extensively in birds and terres-
Ford 共1991兲 grouped all pods that share any call types or
trial mammals 共birds: e.g., Kroodsma and Miller, 1996; Rad-
subtypes into acoustic clans; subclans further define clans
ford, 2004; Beecher and Campbell, 2005; mammals: e.g.,
Seyfarth, 1987; Boughman and Wilkinson, 1998; McComb through use of subclan-specific call types. Relative produc-
et al., 2000兲. However, little is known about how cetaceans tion rates of different call types and whistles vary with broad
utilize their sounds in their natural environment 共Janik, behavioral states of the entire group 共Ford, 1989兲, but in
2000兲, in particular, vocal interactions with conspecifics. Vo- contrast to the AT1 transients, none of the residents’ call
cal signals relate to behavioral contexts in several species, types correlate exclusively with any particular activity 共Ford,
mainly in humpback whales, Megaptera novaeangliae, 1989兲. Rather than reflecting behavioral states, the discrete
bottlenose dolphins, Tursiops truncatus 共see review by Ty- call repertoires are thought to function primarily to maintain
ack, 2000; Janik, 2000兲, southern right whales, Eubalaena cohesion and coordinate activities in intragroup contexts
australis 共Clark, 1982兲, and beluga whales, Delphinapterus 共Ford, 1989, 1991兲.
leucas 共Belikov and Belkovich, 2003兲. Recently, Saulitis There is increasing evidence that the individually dis-
et al. 共2005兲 reported context-specific calls also in the AT1 tinct signature whistles of bottlenose dolphins function as
subpopulation of mammal-eating killer whales or orcas 共Or- cohesion calls when individuals of a social group are sepa-
cinus orca兲 in southern Alaska. Unlike “transient” orcas, the rated 共Janik and Slater, 1998; Watwood et al., 2005兲. Signa-
fish-eating, “resident” orcas of the northeast Pacific live in ture whistles may even facilitate reunions between separated
exceptionally stable matrilineal units 共hereafter termed individuals, especially between calves and their mothers
“matrilines”兲, where offspring of both sexes travel with their 共Smolker et al., 1993兲. Similarly, resident orca matrilines
mothers lifelong 共Bigg et al., 1990; Ford et al., 2000兲. They were recently found to increase the usage of family-specific
are frequently vocal and possess a complex vocal system call types immediately after the births of calves, suggesting
with group-specific dialects 共Ford, 1989, 1991; Yurk et al., that family-specific call types are of profound importance for
2002兲 that remain stable over decades 共Deecke et al., 2000兲 maintaining cohesion within the matriline, in particular be-
tween mothers and their dependent offspring 共Weiß et al.,
a兲 2006兲. Also, call type matching in vocal exchanges within
Current address: Konrad Lorenz Forschungsstelle, Fischerau 11, A-4645
Grünau im Almtal, Austria. Electronic mail: a9400355@unet.univie.ac.at matrilines suggests that the discrete call types of residents
b兲
Electronic mail: Friedrich.Ladich@univie.ac.at function in intragroup communication 共Miller et al., 2004b兲.
3710 J. Acoust. Soc. Am. 122 共6兲, December 2007 0001-4966/2007/122共6兲/3710/7/$23.00 © 2007 Acoustical Society of AmericaIn social species vocal signals are commonly found to TABLE I. Life history parameters of the individuals belonging to the three
matrilines within the A1 pod in the studied timeframe. ID numbers and
not only serve communication within, but also between
demographic data according to Ford et al. 共2000兲.
groups, and call usage and structure frequently change with
the social context 共e.g., Elowson and Snowdon, 1994; Matriline ID Sex Born–Died Mother
Smolker and Pepper, 1999; Hopp et al., 2001; Snowdon and
A12 A12 Female 1941 unknown
de la Torre, 2002; Baker, 2004; Radford, 2005兲. Group size
A31 Male 1958–1997 A12
and composition are known to affect the use of stereotyped
A33 Male 1971 A12
calls in several highly social species, e.g., African elephants A34 Female 1975 A12
共Payne et al., 2003兲 and Northern right whales 共Parks and A55 Male 1989 A34
Tyack, 2005兲. Resident orcas are very social and matrilines A62 Female 1993 A34
regularly travel and interact together irrespective of related- A67 Unknown 1996 A34
ness or degree of call sharing, yet, intergroup communication A74 Unknown 2000 A34
has received little attention and has only come into focus A30 A30 Female 1947 A2
recently. Riesch et al. 共2006兲 described stereotyped whistle A6 Male 1964–1999 A30
types that are shared throughout the Northern resident popu- A38 Male 1970 A30
lation and potentially serve in vocal communication even A39 Male 1975 A30
A50 Female 1984 A30
between members of different acoustic clans. Also, the call
A54 Female 1989 A30
design of several discrete call types suggests that they are
A72 Unknown 1999 A50
long-range communication signals with an active space ex-
A75 Unknown 2001 A54
ceeding by far the distances across which members of a A36 A36 Female 1947–1997 A1
matriline usually separate 共Miller, 2006兲 and the existence of A32 Male 1964 A36
multiple long-range call types suggests a role in intergroup A37 Male 1977 A36
communication. We thus suggest a significant role of discrete A46 Male 1982 A36
calls not only in intragroup, but also in intergroup, commu-
nication of resident orcas. To test this hypothesis, we ana-
lyzed call use of three Northern resident matrilines in intra- were within visual range, changes in any of the previous
and intergroup contexts, i.e., matrilines traveling alone or parameters, as well as times, when the whales passed key
with other matrilines of different relatedness. In particular, landmarks, were noted.
we tested the following predictions: 共1兲 Call use of focal Acoustic data were collected with a hydrophone network
matrilines changes with the presence or absence of other monitored at OrcaLab 24 h a day and year round. Whales
matrilines and 共2兲 changes depend on the identity of the were recorded on a two-channel audio cassette recorder
other matriline共s兲. 共Sony Professional Walkman WM-D6C or Sony TCD-D3兲
with up to six radio-transmitting, custom-made hydrophone
stations 共overall system frequency response 10 Hz– 15 kHz兲
II. MATERIAL AND METHODS whenever they were vocal 共see Weiß et al., 2006兲. Data col-
lection was strictly land based and thus did not interfere with
A. Study animals and data collection or disturb the whales.
Johnstone Strait and adjacent waters off Vancouver Is-
land, British Columbia, form the summer “core area” for the
B. Acoustic analyses
Northern resident community of orcas, which consists of
more than 200 individually known orcas in three acoustic Focal matrilines were frequently observed and recorded
clans 共Bigg et al., 1990兲. The focus in this study was on three with matrilines from different pods 共closely related
closely related matrilines, A12, A30, and A36, comprising matrilines兲, subclans, and clans. For investigating the intra-
the most commonly encountered pod, A1 共Ford et al., 2000兲. and intergroup vocal behavior we selected recordings where
In October 2002, they consisted of 7, 7, and 3 individuals, focal matrilines were encountered in one of five clearly de-
respectively 共Table I兲. fined social contexts: 共1兲 alone, 共2兲 together with the other
Visual data were obtained at OrcaLab, located centrally two A1 matrilines 共“same pod”兲, 共3兲 in the company of
in the study area 共50° 34⬘N and 126° 42⬘W兲, and through a matrilines belonging to a different pod within the same
network of observers: OrcaLab volunteers stationed at field acoustic subclan 共“same subclan”兲, 共4兲 in the company of
stations, other independent researchers, and whale watch op- matrilines belonging to a different subclan within the same
erators. Data from all sources were integrated and summa- clan 共“other subclan”兲, or 共5兲 in the company of matrilines
rized on a daily basis. The waterways were routinely sur- belonging to a different clan 共“other clan”兲. “Alone” referred
veyed with spotting scopes; visual observations were done to situations in which only the focal matriline was seen or
on an opportunistic basis, whenever whales were seen or heard within the same or adjacent hydrophone range共s兲. A
heard within the vicinity of a station. Upon sighting, the focal matriline was considered to be in the company of an-
number and identity of individuals 关based on ID catalog other matriline when both were observed within acoustic
共Ford et al., 2000兲兴, group composition, group cohesion, di- range of each other, were heading in the same direction and
rection of movement, and behavioral state 共travel, motion- were engaged in the same behavior. Distances between
less, forage, or socialize兲 were recorded. As long as whales matrilines traveling in company were estimated with the help
J. Acoust. Soc. Am., Vol. 122, No. 6, December 2007 Weiß et al.: Orca vocal behavior and group composition 3711TABLE II. Number of samples, calls and recording days of focal matrilines avoid a bias towards call types of higher amplitude 共see
in varying social contexts.
Miller and Tyack, 2001兲. The remaining data were split into
Matriline With n samples n calls n days samples of 100 calls. Preferably, samples were chosen from
different recording days. However, because selection criteria
A12 ... 10 983 7
strongly reduced the number of usable samples in some of
A12 Other pod 6 570 3
A12 Other subclan 2 181 1 the defined social contexts, we also included recordings with
A12 Other clan 2 159 1 less than 100, but a minimum of 75 calls. For the same
A30 ¯ 15 1500 14 reason, we sometimes used multiple samples from the same
A30 Other pod 4 353 3 day, but as widely separated in time as possible and never
A30 Other subclan 2 186 1
more than three to maximize statistical independence of the
A30 Other clan 6 550 4
A36 ¯ 10 965 7
data 共Table II兲. For each sample, we determined percentages
A36 Other pod 3 258 3 of call use per call 共sub-兲type as well as the call rate 共n
A36 Other subclan 4 366 2 calls/minute/individual兲 and the number of different call
A36 Other clan 9 810 6 types used.
A12+ A30+ A36 8 783 4 Data were analyzed using the SPSS® statistical pro-
gram. As data clearly deviated from normal distribution
of landmarks and were typically well below 1000 m. We 共Shapiro-Wilk, all parameters p ⬍ 0.02兲, they were tested
only used recordings for further analysis during which the nonparametrically. Also, data were tested separately for each
spacing, direction of travel, and behavioral states of the in- matriline, as basic call use differs somewhat between the
volved matrilines were observed from shore or were reported three focal matrilines 共Miller and Bain, 2000; Weiß et al.,
from whale watching boats, and that allowed definite attribu- 2006兲. Frequencies of call types and numbers were compared
tion of calls to the matrilines in a defined situation. This between single focal matrilines and focal matrilines in com-
excluded night-time recordings as well as those where one or pany using Mann-Whitney-U tests. Because calls could not
more additional matrilines were seen and/or heard within be reliably attributed to the producing matriline when all
range of the same hydrophone as the defined matriline共s兲. three focal matrilines were recorded together, we did not
The selected recordings were obtained between 1989 and compare recordings of the three matrilines together with
2002 except for one recording of the A30 and B7 matrilines,
those of the single matrilines, but rather with several aver-
that was obtained in August 2005. The predominant behav-
aged samples 共frequency of a given call type for A12
iors were traveling and/or foraging.
Calls were classified according to Ford 共1987, 1989, + A30+ A36 divided by 3兲. In those cases, where call use did
1991兲 by simultaneous acoustic and visual inspection of son- differ between the single and the company contexts, we con-
agrams, generated with Cool Edit 2000 共Syntrillium Soft- ducted Kruskal-Wallis tests to further test for differences in
ware Corporation兲 or Raven 1.2 共Cornell Lab of Ornithol- call use depending on the identity of the company. Compari-
ogy兲. Two call subtypes, N5iii and N9iv 共Weiß et al., 2006兲, sons of call use between each single social context were not
were additionally distinguished because they were family feasible due to an n below 5 in 6 of 9 of the company con-
specific to focal matrilines. texts. We did not consider alpha correction for multiple test-
ing, because of an increased risk of type-II error due to small
C. Statistical analyses sample sizes 共Nakagawa, 2004兲. Call types with rates of oc-
If more than 5% of calls were not both visually and currence below 1% in any context were included in the cat-
acoustically recognizable because of poor signal-to-noise ra- egory “other” for the given matriline. All statistical tests
tio, recordings were excluded from statistical analysis to were two-tailed.
FIG. 1. Call use of all three focal
matrilines traveling on their own or
with each other. ab, aberrant and var,
variable. Bars show median percent-
age of total calls and first and third
quartiles. Asterisks mark significance
levels: * = p ⬍ 0.05; ⫻ = p ⬍ 0.06; and
n = 8 共alone兲 and 9 共together兲.
3712 J. Acoust. Soc. Am., Vol. 122, No. 6, December 2007 Weiß et al.: Orca vocal behavior and group compositionFIG. 2. Call use of the A12 matriline
traveling on its own or with whales
from different pods or 共sub-兲clans. ab.,
aberrant; var., variable; and imit., imi-
tation. Bars show median percentage
of total calls and first and third quar-
tiles. Asterisks mark significance lev-
els: * = p ⬍ 0.05; * * = p ⬍ 0.01; and n
= 10 共alone兲 and 10 共with company兲.
III. RESULTS the A12 matriline, the family-typical call subtype, N9iv, was
Altogether, 81 samples totaling 7664 calls of focal used significantly more often in the presence of other groups,
matrilines on their own or in the company of other groups which was also the case for variable calls 共Mann-Whitney U
were of sufficient quality for statistical analysis 共Table II兲. test, N9iv: n = 26, U = 25, p = 0.003, variable: n = 26, U
Call patterns when matrilines were alone were comparable to = 21.5, p = 0.001兲. On the other hand, N1, N3, N7, N8 and
those described by Miller and Bain 共2000兲 and Weiß et al. N9i calls made up significantly higher portions of the call
共2006兲 for the three focal matrilines. repertoire when the matriline was recorded on its own
With the exception of N3 calls and N10 calls, mean call 共Mann-Whitney U test, N1: n = 26, U = 41.5, p = 0.041, N3:
use of the single A1 matrilines was very similar to that of the n = 26, U = 24, p = 0.002, N7: n = 26, U = 33, p = 0.012, N8: n
A1 matrilines traveling together 共Fig. 1兲. N3 calls made up a = 26, U = 32, p = 0.01, N9i: n = 26, U = 34.5, p = 0.014兲. With
significantly smaller proportion of calls when all three A1 up to 10% change in call use, differences were more pro-
matrilines were together 共Mann-Whitney U test, n = 17, U
nounced in the A36 matriline than in the A12 matriline.
= 9, p = 0.008兲, while the use of N10 calls tended to increase
The use of some call types also differed depending on
in such situations 共Mann-Whitney U test, n = 17, U = 16, p
= 0.059兲. which group accompanied a focal matriline 共Fig. 5, Kruskal-
In the presence of more distantly or unrelated matrilines Wallis test, A12—aberrant: n = 10, H = 5.595, p = 0.061,
from other pods/clans, the A12 matriline was found to in- A36—N7: n = 10, H = 5.854, p = 0.054, A36—variable: n
crease the use of the family-typical N5iii, as well as aberrant = 10, H = 6.014, p = 0.049兲, which suggests that changes in
and imitation calls 共Fig. 2, Mann-Whitney U test, N5iii: n call use may not only have been affected by the presence of
= 20, U = 22.5, p = 0.035, aberrant: n = 20, U = 20, p = 0.023, other groups, but also by their identity. However, sample
imitation: n = 20, U = 15, p = 0.007兲. In each case, changes in sizes in the different conditions were low and more detailed
call use were below 5%. Although we did not find any sig- analyses were not feasible.
nificant differences in call use of the A30 matriline traveling Focal matrilines did not differ in their call rate 共n calls/
with or without company 共Fig. 3兲, they used the family typi- minute/individual兲 nor in the number of different call types
cal N47 call 2–3 times more often in the presence of
used in any of the contexts 共Kruskal-Wallis test, all p ⬎ 0.1,
B-subclan for which two samples were available. The A36
Mann-Whitney U test, all p ⬎ 0.1兲.
matriline showed a number of distinct changes 共Fig. 4兲. As in
FIG. 3. Call use of the A30 matriline
traveling on its own or with whales
from different pods or 共sub-兲clans. ab.,
aberrant and var., variable. Bars show
median percentage of total calls and
first and third quartiles. n = 15 共alone兲
and 12 共with company兲.
J. Acoust. Soc. Am., Vol. 122, No. 6, December 2007 Weiß et al.: Orca vocal behavior and group composition 3713FIG. 4. Call use of the A36 matriline
traveling on its own or with whales
from different pods or 共sub-兲clans. ab.,
aberrant and var., variable. Bars show
median percentage of total calls and
first and third quartiles. Asterisks mark
significance levels: * = p ⬍ 0.05. * *
= p ⬍ 0.01; and n = 10 共alone兲 and 16
共with company兲.
IV. DISCUSSION tent changes were increases in the use of family-specific call
subtypes as well as variable and aberrant calls in the pres-
This study presents evidence that resident orca
ence of orcas from other groups. Changes in call use were
matrilines change their vocal behavior in intergroup contexts.
typically well below 10% and thus less pronounced than the
Consistent with our predictions, percentages of call types
changes observed in call use in another social context, i.e.,
used by focal matrilines depended on the presence or ab-
after the birth of a calf 共Weiß et al., 2006兲.
sence of additional matrilines in two out of three studied
The focal matrilines differed considerably in the number
matrilines; findings for the third matriline were also consis-
of call types with emission rates affected by the social con-
tent in key respects, though sample sizes were small and the
text. The A36 matriline showed significant changes in call
changes were not statistically significant. The most consis-
use in half of their repertoire 共7 of 14 call types兲, the A12
matriline to a considerably lesser extent 共3 of 15 call types兲,
and there were no statistically significant changes at all in the
A30 matriline. However, their family typical N47 call was
used 2–3 times as often in the presence of B-subclan
matrilines and interestingly, changes in the A36s’ acoustic
behavior were also strongest in the presence of matrilines
from B-subclan.
To some extent, the differences in call use may reflect
low sample sizes for some matrilines in some contexts; how-
ever, it is also possible that they reflect different social roles
arising from differences in associations and movement pat-
terns. At least one of the three focal matrilines is present in
the study area, almost daily, during each summer and fall
共Symonds and Spong, private communication兲. Changes in
call use exhibited by the A1 matrilines thus may reflect dif-
ferences in the manner in which each of the matrilines re-
sponds to intergroup situations involving the other, less com-
monly visiting Northern resident groups in the Johnstone
Strait area, and they may underscore possible differing social
roles within their own pod and community. Just how each of
the A1 matrilines performs its role and specifically what
these roles might be is beyond the scope of this study, how-
ever, the indication that matrilines within a pod have possible
different roles should encourage further investigation.
It also seems possible that some of the changes we ob-
served reflect differences in the age and sex composition of
individual matrilines. Indeed, the three focal matrilines do
differ in this respect; the A36 matriline consisted of only one
female and her three adult sons prior to the matriarch’s death
FIG. 5. Use of 共a兲 N7 calls and 共b兲 variable calls by the A36 matriline in in 1997, and since then only of adult males, whereas the
different social contexts 共focal matriline alone, with matrilines from the
other two matrilines each added a new generation during the
same subclan, another subclan or another clan兲. Bars show median percent-
age of calls and first and third quartiles. Numbers of samples appear above study period. Studies of other species show that vocal signals
the bars. can convey not only individual or group-specific informa-
3714 J. Acoust. Soc. Am., Vol. 122, No. 6, December 2007 Weiß et al.: Orca vocal behavior and group compositiontion, but also age and sex-specific cues that may remain dis- functions in intra- and intergroup communication, such as
tinguishable even when transmitted over greater distances directionality cueing and thus indicating one’s location and
共e.g. Green, 1981; Rendall et al., 2004; Blumstein and Mu- direction of movement 共Miller, 2002兲.
nos, 2005兲. Animals may respond differently to calls of In conclusion, the presence and identity of accompany-
males and females 共e.g., Vicario et al., 2001; Miller et al., ing matrilines significantly affected calling behavior of resi-
2004a兲 or may respond differently to signals depending on dent orca matrilines. The observed changes seem to reflect
their own sex 共Rogers et al., 2006兲. It is plausible, therefore, call functions in both intragroup, as well as intergroup, com-
that the differences in call use among our focal matrilines munication, and differences between matrilines hint at pos-
stemmed partly from different age or sex distributions in the sible different social roles within the community. To get a
focal or the accompanying matrilines. However, as virtually better understanding of these roles, we will need extensive
nothing is known about age or sex differences in the call use data sets of individual calling behavior along with precise
of wild orcas, this idea remains purely speculative. behavioral observations. Both are currently extremely diffi-
At least in some call types, changes in use seemed not cult to obtain, but provide potentially fruitful challenges for
only dependent on the mere presence of nonfocal matrilines, future research.
but to some degree on whether these nonfocal whales were
ACKNOWLEDGMENTS
from a pod within the same subclan, from a different sub-
clan, or from an entirely different clan, i.e., whales that differ The authors wish to thank Anna Spong and OrcaLab
both in the degree of relatedness and of call type sharing. assistants for continuous recording and observation efforts.
Although the focal matrilines share almost all call types with Also, they are grateful for the contributions of observers,
whales within the same subclan, they share few with those researchers, and whale-watchers in the Johnstone Strait area,
from a different subclan and none with whales from a differ- especially the late Michael Bigg, Graeme Ellis, and John
ent clan 共Ford, 1987, 1991兲. Studies in other species have Ford. The study was supported by a doctoral scholarship of
shown that the degree of vocal sharing may play an impor- the Austrian Academy of Sciences to B.M.W.
tant role in acoustic communication between groups and in-
dividuals. For instance, song sparrows, Melospiza melodia, Baker, M. C. 共2004兲. “The chorus song of cooperatively breeding laughing
kookaburras 共Coraciiformes, Halcyonidae: Dacelo novaeguineae兲: charac-
were more likely to perceive a song as directed at them if the terization and comparison among groups,” Ethology 110, 21–35.
song was shared than if it was unshared 共Beecher and Camp- Barrett-Lennard, L. G. 共2000兲. “Population structure and mating patterns of
bell, 2005兲; and great tits, Parus major, responded differ- killer whales, Orcinus orca, as revealed by DNA analysis,” Ph.D. thesis,
University of British Columbia, Vancouver.
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