ISSN 1063-7710, Acoustical Physics, 2007, Vol. 53, No. 4, pp. 528534. Pleiades Publishing, Ltd., 2007.Original Russian Text R.A. Belikov, V.M. Belkovich, 2007, published in Akusticheski

Zhurnal, 2007, Vol. 53, No. 4, pp. 601608.

528

INTRODUCTIONSounds produced by odontocete cetaceans (

Odonto-ceti

) are conventionally divided into two main physicalcategories: (i) pulsed sounds (clicks) and (ii) continu-ous narrowband signals (whistles) [1]. Whistles arebelieved to play an exceptionally important role in thecommunication of odontocete cetaceans, especially,animals from the

Delphinidae

family [1]. According tothe general concept, the more social the species is, themore important the role of whistles in their communi-cation [1] (although, some exceptions are known, suchas sperm whales (

Physeter macrocephalus

) [2] andkiller whales (

Orcinus orca

) [3]).It is believed that dolphins produce a large set of

whistles with different frequency contours, which arecommon to all individuals and form the repertory ofwhistles of a given species and/or population [4]. Therepertory of whistles of odontocete cetaceans repre-sents not a discrete but a gradual system with smoothtransitions between different types [1]. Dolphins arecharacterized by a high differential sensitivity to abso-lute timefrequency parameters of whistles [5]. In addi-tion, they are capable of perceiving the relative fre-quency contour (i.e., the shape of the contour) of whis-tles [6] and, presumably, can use the information on therelative energy distribution between the whistle har-monics (i.e., on the timbre of whistles) [7].

Whistles play an important role in mediating dol-phin group cohesion and coordination [8]. Some of thespecies of

Delphinidae

are assumed to possess signa-ture whistles [9] (however, an opposite point of viewwas put forward in [10]). Signature whistles are defined

as stereotyped individual-specific identification sig-nals, which are used by group members as long-rangecohesion calls in situations where individuals arebeyond the range of vision of each other [9, 11]. At thesame time, one of the species of the

Delphinidae

fam-ily, namely, killer whales, whose whistles are the mostcomplex and long among those of

Delphinidae

, wasfound to use whistles as short-distance emotion signalsin close social interactions [12, 13].

The beluga whale (

Delphinapterus leucas

Pall.) is awide-spread and most numerous species of odontocetecetaceans in the Arctic. Beluga whale belongs to the

Monodontidae

family, which is included together withthe

Delphinidae

and

Phocoenidae

families into the

Delphinoidea

superfamily [14]. Owing to its highacoustic activity and rich vocal repertory including amultitude of twittering sounds, the beluga whale haslong been referred to as a marine canary bird. Bioa-coustic studies are expected to shed light over the pop-ulation structure of this species. So far, the vocal reper-tories of different beluga whale populations have beenstudied in the Canadian High Arctic [15], in theSt. Lawrence Estuary [16], in Bristol Bay of Alaska[17], and near Spitzbergen Island [18]. Considerableprogress in understanding belugas vocal behaviorunder natural conditions, including search and huntingbehavior, was achieved owing to long-term studies ofbeluga whales in the White Sea and in the Amur Estu-ary [19]. These studies were the first to reveal the geo-graphic variability in the belugas acoustic behavior[19]. However, the vocal repertories of beluga whales

ACOUSTICS OF LIVING SYSTEMS.BIOACOUSTICS

Whistles of Beluga Whales in the Reproductive GatheringOff Solovetskii Island in the White Sea

R. A. Belikov and V. M. Belkovich

Shirshov Institute of Oceanology, Russian Academy of Sciences,Nakhimovski

pr. 36, Moscow, 117997 Russiae-mail: rbelikov@ocean.ru, romanbelik@rambler.ru

Received May 25, 2006

Abstract

Whistles recorded in a reproductive gathering of beluga whales near Solovetskii Island in the WhiteSea are analyzed. On the basis of the absolute characteristics and shape of the frequency contour, whistles areclassed into 16 types. Whistles belong to a relatively low frequency band, contain many harmonics, and have asimple shape of frequency contour. The average whistle duration varies from 0.1 to 1.7 s for different types, theaverage value of the maximum fundamental frequency varies from 1.4 to 4.5 kHz, and the average number ofinflection points is from 0 to 9 per signal. In contrast to other populations, where flat whistles are the most fre-quent vocalizations, beluga whales observed in the reproductive gathering in the White Sea most often produceshort whistles with a V-shaped frequency contour.PACS numbers: 43.80.Ka

DOI:

10.1134/S1063771007040148

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WHISTLES OF BELUGA WHALES 529

in these two parts of the areal have not yet received anyobjective detailed quantitative description.

A characteristic feature of the belugas rich vocalrepertory is the variety of pulsed sounds and noisy calls[1519]. However, a considerable and, often, a predom-inant part of the belugas vocal production consists oftone signals [15, 17, 18, 20]. Their purpose is stillpoorly understood [20, 21]. It was assumed that the bel-ugas whistles are mainly of an emotional nature [19].Indeed, it was found that whistles are most frequentlyproduced by belugas in the course of social interactions[16]. It is remarkable that whistles are also likely to beused for long-range communication between groups,but not for the coordination of group movements [16].

The frequency and time parameters of tone signalsand the structural characteristics of their contours wereoften used to compare the repertories of different spe-cies and populations of cetaceans [2226]. For many ofthe

Odontoceti

species, tonal signals represent the mostsuitable physical category for revealing the geographicvariability of acoustic repertories.

In addition to studying the geographic variability, adetailed quantitative description of vocalizations typi-cal of beluga whales of the White Sea is topical becauseof the growth of the antropogenic effect on these ani-mals in the last few years [27, 28]. For example, thereproductive gathering (RG) of beluga whales of theSolovetskii local stock has become an object of com-mercial tourism. In addition, ship traffic near theSolovetskii Island has become much more intense. As aresult, the noise pollution in the area of the RG of bel-uga whales considerably increased. Remember thatRGs are seasonal critical habitats, which are necessaryfor the reproduction and the sustention of the socialstructure of subpopulations [29]. Evidently, vocal com-munications play an exceptionally important role inthese processes. Hence, in view of the growth of antro-pogenic noise, knowledge of the exact characteristics ofthe belugas vocalizations is necessary not only forunderstanding their biological significance, but also forevaluating the risk associated with the effect of humanactivity on these animals.

The purpose of the present study is the acousticanalysis and quantitative description of whistles pro-duced in the RG by the belugas of the Solovetskii localstock.

MATERIALS AND METHODSWhistles were understood as continuous narrow-

band signals with a fundamental frequency of up to5 kHz. Signals of higher frequencies were ascribed to aseparate group of high-frequency whistles, which weredescribed by us in detail in our previous publication[30]. Earlier, we separated the group of high-frequencysignals primarily on the basis of bimodality (a dip near5 kHz) of the distribution of belugas tonal signals infrequency [30].

Data were collected during JuneAugust of 1997and 19992003 in a reproductive gathering of belugawhales off Beluzhii Cape (

6543

N;

3531

E) ofSolovetskii Island in the White Sea. The gatheringunder study amounted to 120 individuals. It was formedevery year in mid-May and disintegrated in early Sep-tember. It consisted predominantly of females withcalves of various ages; in addition, it often includedseveral mature males. Within the range of hydrophoneoperation, beluga whales could form several compactgroups of up to 60 individuals.

Sounds produced by belugas were recorded by asystem consisting of a stationary spherical hydrophone,an amplifier, and a Sony-MZ35 MD recorder (or aVesna-212/Ritm-320 cassette recorder) with a flat fre-quency response (

3

to 4.5 dB) of up to 1420 kHz(depending on the type of recorder). A total of 230 h ofrecords was obtained.

The preprocessing of experimental data was per-formed using the Cool Edit Pro 1.2 software. We syn-chronously listened to the records and watched scroll-ing color-enhanced spectrograms (an FFT size of 256points and a Hamming window) or oscillograms. Atotal of 1046 whistles with a high signal-to-noise ratiowere sampled for further analysis.

Acoustic measurements of the belugas whistleswere performed using moving cursors in the Syrinx 2.1software (developed by J. Burt from Cornell Univer-sity). The following characteristics of whistles weremeasured: the signal duration; the beginning, ending,minimal, and maximal fundamental frequencies; thedominant frequency; the total number of harmonics; thenumber of the dominant harmonic; and the number ofinflection points in the frequency contour. The statisticsof the belugas whistles was described using the Statis-tica 5.0 software package (StatSoft, Inc.). We deter-mined the arithmetic mean, the standard deviation, andthe minimal and maximal values of the whistle typeparameters.

To determine the rates of occurrence (signal/min)and percentage (%) of signals of each of the types in thetotal vocal production of beluga whales, from the initialset of high-quality records, we choose in a random way152 fragments with durations of 2 min each. Withineach of the fragments, we counted all of the signals byusing scrolling color-enhanced spectrograms (a 5-sviewing window) in the Cool Edit Pro 1.2. A total of15653 signals were counted.

In the area of observation, we also encounteredringed seals,

Phoca hispida

, and bearded seals,

Erig-nathus barbatus

. Records that were made in the pres-ence of seals in the area under study were rejected. Webelieve that all of the signals analyzed by us belong tobeluga whales alone.

530

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BELIKOV, BELKOVICH

RESULTSWhistles (W) represent the most numerous and typ-

ical sounds produced by belugas in the RG. We classedthem into 16 types (see figure). The rate of occurrenceof whistles in the fragments of records under analysis ison the average

22.5

13.1

signal/min (while the totalrate of occurrence of all the communicative signals is

48.7

23.9

signal/min). The whistles make about 49%(

n

= 7683, where

n

is the number of counted whistles)of all communicative signals (

N

= 15653, where

N

isthe total number of recorded communicative signals) ofbeluga whales. The major part of whistles belongs totwo whistle types: squeak (W1, 23%) and chirrup (W2,14%). A considerable part (7.5%) of whistles is repre-sented by a group of three flattened whistles (W5W7).The part of whistles including 11 other types is as smallas approximately 4.5% of all communicative signals,while each of these types makes up only 0.01 to 3.0%.

The whistles were classed into 16 types by aural andvisual perception. We classed them on the basis of boththe shapes of their frequency contours (flattened, rising,descending, V-shaped, etc.) and their absolute timefre-quency characteristics (such as central frequency, fre-

quency band, and signal duration). Signals with thesame shape of contour but different absolute character-istics were ascribed to different types if intermediateforms of signals were absent or rare.

The parameters of whistle types are presented in thetable, while spectrograms of representative signals aredisplayed in the figure. Analysis showed that whistlesare continuous, mid-frequency, narrowband soundsusually containing many harmonics. The average dura-tion of whistles varies from 0.1 to 1.7 s for differenttypes. However, the most-used signals have small (0.10.2 s) or intermediate durations (0.71.2 s). The aver-age values of maximum fundamental frequencies varyfrom 1.4 to 4.5 kHz, while the frequency band between2 and 3.5 kHz is used most frequently. As a rule, formost of the whistle types, the energy maximum in thewhistle spectrum corresponds to one of the higher har-monics (most often, second to fourth), and, therefore,the dominant frequency usually lies in the frequencyband from 4 to 8 kHz.

The majority of the belugas whistles in the RG havesimple shapes of frequency contours. The basic set ofcontours used by the animals is limited. It includes flat-

1

4

8

12

2

W13

Time, s

Freq

uenc

y, kH

z

1 2

W14

1 2

W15

1 2

W16

4

8

12W9 W10 W11 W12

4

8

12W5 W6 W7 W8

4

8

12W1 W2 W3 W4

Spectrograms of representative whistles (W) of beluga whales. Types W1W16. Spectrogram parameters: an FFT size of 256 pointsand a Hamming window. The spectrograms are obtained with the Syrinx 2.1 software. Types W2, W3, and W16 are represented bymulticomponent signals. Spectrograms of W1, W3W5, W8W13, and W15 contain more than one signal of a corresponding type.Spectrograms of W3 and W12 contain a pulsed tone with a low pulse repetition rate and a fragment of a noise-polluted high-fre-quency whistle (with a fundamental frequency of ~8 kHz), respectively.

ACOUSTICAL PHYSICS

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WHISTLES OF BELUGA WHALES 531

tened, rising, descending, descendingrising, risingdescending, and, possibly, wavy contour shapes. TheV-shaped contour typical of the W1 and W2 types ofwhistles is used most often. Owing to the small dura-tion, narrow fundamental frequency band, and smallnumber of bends and inflections of the frequency con-tour, the belugas whistles have a simple form. How-ever, the form of signals, as well as their absoluteparameters, is subject to certain variability within agiven type.

Whistles with a flat contour shape are of relativelyrare occurrence (~2% of all communicative signals)among the beluga whales in the RG. Therefore, we con-sidered them as part of a more extended group, whichwe called flattened whistles. The flattened whistles are

characterized by a considerable duration and a rela-tively long (the major part of a signal) flattened portionwithin which the frequency remains approximatelyconstant. In these whistles, the most variable parts ofthe contour are the beginning and the ending parts,which may be curved upwards or downwards.

Flattened whistles seem to occupy an importantplace in communication between beluga whales. Itshould be noted that the variability of the shapes of fre-quency contours is combined with the stability of themean fundamental frequency. This suggests that themean frequency of a contour is a more significant char-acteristic than the bends of its beginning and/or endingparts. Therefore, flattened whistles were classed by usinto three types: W5, W6, and W7 with mean frequen-

Characteristics of whistles (W) produced by beluga whales. The set of values consists of the arithmetic mean

standard de-viation and the minimum and maximum values;

n

is the sample size; % shows the percentage of a given whistle type fromthe total number of communicative signals (i.e., 15653)Whistle

type (W)

n

% Duration, sFundamental frequency, kHz Points of

inflectionDominant harmonic number

Peak fre-quency,

kHzNumber of harmonicsBeginning End Minimal Maximal

W1 300 23 0.10

0.100.020.42

2.9

0.41.84.5

3.1

0.42.04.2

2.3

0.31.33.3

3.2

0.42.14.5

1.2

0.513

2.2

0.614

6.1

1.72.111.9

4.8

1.3211

W2 130 14 1.09

0.730.204.46

3.1

0.61.85.0

3.3

0.82.26.5

2.6

0.61.85.0

3.5

0.82.06.5

9.0

6.8038

2.0

0.614

6.3

2.12.213.4

4.6

1.027

W3 14 0.01 0.90

0.270.490.90

2.4

0.21.92.4

2.2

0.21.92.2

2.1

0.21.92.1

2.4

0.12.22.4

0.2

0.400.4

1.0

0.011

2.2

0.12.02.2

5.4

1.237

W4 85 0.20 0.32

0.190.051.18

2.4

0.61.14.9

2.4

0.71.05.1

2.1

0.61.04.9

2.6

0.61.45.1

0.2

0.402

1.1

0.312

2.4

0.81.55.3

5.7

1.438

W5 130 4.30 1.06

0.500.272.78

1.8

0.40.93.3

2.0

0.40.63.7

1.7

0.30.62.3

2.1

0.31.53.7

1.0

2.2016

4

1.517

6.9

2.81.612.5

6.5

1.749

W6 135 2.50 1.30

0.870.094.82

2.7

0.61.53.8

2.9

0.31.74.0

2.5

0.51.33.6

3.1

0.32.04.5

1.5

3.3025

1.0

0.514

5.6

1.42.59.5

4.5

1.037

W7 52 0.70 0.90

0.490.242.08

2.0

0.62.56.0

4.1

0.72.15.7

3.7

0.62.15.1

4.5

0.43.76.0

1.5

1.808

1.5

0.512

6.2 2.23.49.3

3.2 0.814

W8 16 0.04 1.40 0.400.902.10

3.0 0.62.14.2

3.0 0.62.44.3

2.6 0.42.13.5

3.7 0.43.24.5

3.1 1.326

1.0 0.011

3.0 0.52.34.1

3.4 0.824

W9 8 0.23 0.63 0.190.430.94

1.4 0.30.81.7

2.9 1.51.46.2

1.2 0.30.81.7

3.1 1.51.46.2

0.5 0.802

2.3 1.415

3.8 1.81.66.0

7.8 2.1512

W10 36 0.67 0.80 0.300.341.61

1.4 0.20.91.7

2.2 0.21.62.7

1.4 0.20.91.7

2.2 0.21.72.7

3.8 4.1012

3.0 0.814

4.4 1.51.37.9

6.7 0.858

W11 8 0.01 0.97 0.150.801.27

1.0 0.10.91.3

1.9 0.11.72.1

1.0 0.10.91.3

2.1 0.11.92.3

1.0 0.011

2.9 0.624

3.0 0.71.84.1

8.0 0.879

W12 23 0.10 0.57 0.120.300.73

0.7 0.10.61.0

0.6 0.10.40.9

0.6 0.10.40.9

1.4 0.21.01.8

1.0 0.011

1.0 0.212

0.8 0.10.61.2

3.4 2.4112

W13 44 0.30 0.45 0.140.160.79

2.3 0.51.54.0

0.7 0.20.31.4

0.7 0.20.31.4

2.4 0.51.64.0

0.0 0.000

1.1 0.514

2.2 1.31.29.3

5.8 2.8 110

W14 41 0.01 0.85 0.300.071.89

4.0 0.33.24.7

1.9 0.31.52.8

1.9 0.31.52.8

4.0 0.23.34.7

0.0 0.000

1.0 1.212

3.4 0.52.46.1

4.4 1.036

W15 17 3 0.10 0.030.060.15

1.9 0.41.32.6

0.8 0.30.51.4

0.7 0.30.41.3

1.9 0.41.32.6

0.8 0.401

1.0 0.011

0.9 0.30.51.3

2.4 1.215

W16 9 0.01 1.73 0.840.572.87

2.3 1.01.33.6

0.6 0.20.41.0

0.5 0.20.41.0

2.3 0.91.53.6

0.00.000

1.4 0.813

2.0 0.90.83.0

3.7 1.325

532

ACOUSTICAL PHYSICS Vol. 53 No. 4 2007

BELIKOV, BELKOVICH

cies of 2, 3, and 4 kHz, respectively. Within each ofthese types, several subtypes can be distinguishedaccording to the details of the contour shape. The mostwidespread subtype is the risingflat one.

Among the whistles of beluga whales in the RG, nowhistle type exclusively characterized by a wavy fre-quency modulation could be detected. Indeed, the W8signals cannot be called truly wavy, because, as a rule,a signal includes no more than two inflection pointsand, hence, no more than 1.5 modulation periods. Onthe other hand, a wavy frequency modulation is oftenobserved for whistles of different types (see, e.g., thespectrogram of the second signal of the W10 type). Pre-sumably, the modulation should be considered not asthe type-determining feature, but as a common propertyof different signals that manifests itself under certainconditions: for example, when the animals are in a stateof strong emotional excitation.

Multicomponent whistles can be conventionallydivided into two groups: multiplicated (formed by mul-tiple repetition of identical elements) and segmentedones (formed by segmentation, i.e., division of the ini-tially single contour into several parts, which may havedifferent shapes). The main difference between thesetwo groups lies in that the segmented whistles have pro-totypes with a single contour. Beluga whales from theRG near Solovetskii Island produce three types of mul-tiplicated whistles (W2, W3, and W16), which consistof repeated short isomorphic elements. In addition, bel-ugas have two subtypes of segmented whistles: a risingstraight subtype of W7 and a segmented subtype of W8.It should be noted that the interpretation of the W8 sig-nal structure is ambiguous, because individual seg-ments of the contour often partially overlap.

It is believed that the system of signals used by bel-ugas is highly gradual [1518]. Our analysis confirmsthis statement. Among the multitude of whistles, oneshould primarily notice the smooth transition betweenW1, W2, and W6. In the framework of this transition, aW1 signal may gradually elongate through the forma-tion of the ending part (tail) with a relatively constantfrequency. As the ending part elongates and is frag-mented, the W1 signal can transform into W2. Then, asa result of a reduction of the frequency modulation anda decrease in the intervals between elements, the W2signal can transform into W6.

It is also worth noting that whistles were often pro-duced together with a pulsed signal, which, as a rule,was a pulsed tone with a low pulse repetition rate.

DISCUSSIONThe subjectivity of operators and the distinctions in

the methods of signal classification, as well as an insuf-ficient amount of high-quality spectrograms and repre-sentative signal records, make the comparison of thebelugas vocal repertories a rather complicated prob-lem. However, the analysis of the belugas whistles

showed that six out of seven basic contour types (CT)described earlier in [15], which are likely to be typicalof all the populations studied [1618], are present in therepertory of the beluga whales observed in the RG inthe White Sea. Only signals corresponding to CT7(trill) are absent. However, it is possible that signalsdescribed as CT7 are still produced by the White Seabelugas. For example, a certain similarity can be foundbetween these signals and the W2 signals of the belugasin the White Sea. Unfortunately, because of the draw-backs in the definition of CT7 in [15], this issuerequires further investigation.

It is believed that belugas from Bristol Bay andSpitzbergen Island [17, 18] possess signal types that arenot encountered among the belugas from the CanadianHigh Arctic [15]. Comparison of whistle types (S1 andS2) that are exclusively typical of Spitzbergen belugas[18] with our data showed that belugas of SolovetskiiIsland do not produce such whistles. Concerning thewhistle types (7, 9, 10, and 13) that are uniquely asso-ciated with the belugas of Bristol Bay [17], it is difficultto make any definite conclusions, because the defini-tions of these types on the basis of duration and finestructure of the contour in [17] make the comparisonfairly difficult. For belugas of the White Sea, uniquesignals are multicomponent whistles W3 and W16 andsignals W8, HFWT4, and HFWT10 [30]. However,since these signals are of very rare occurrence, it is pos-sible that they could not be detected in other popula-tions simply because of the insufficient amount ofrecords.

Beluga whales of Solovetskii Island, as well as theanimals found near Spitzbergen Island [18] and in Bris-tol Bay [17], have a much smaller number of (sub)typesof multicomponent whistles, as compared to the belu-gas of Cunningham Inlet [15] and St. Lawrence Estuary[16]. We found only two subtypes of segmented whis-tles (for W7 and W8). Nevertheless, multicomponentwhistles, namely, multiplicated ones, i.e., whistlesformed by the repetition of isomorphic elements, weresufficiently numerous in the acoustic production ofSolovetskii belugas. However, the predominant part ofthese signals was represented by only one type: W2(chirrup).

It is believed that segmentation of the whistle con-tour increases the detectability of the signal. It isassumed that segmentation is used by animals forincreasing the reliability of whistle perception in long-range communication and in the presence of high-levelambient noise [15, 16, 20]. Indeed, we found that seg-mentation of the contour is characteristic of the bel-ugas whistles in the case of long-range communicationin the open sea [31]. In addition, we also noticed that,in the last few years (20042005), the number of seg-mented whistles of belugas observed in the RG near theBeluzhii Cape has become greater, which may becaused by the change in the ambient noise level due toship traffic.

ACOUSTICAL PHYSICS Vol. 53 No. 4 2007

WHISTLES OF BELUGA WHALES 533

The durations of whistles produced by belugas atdifferent sites of the species geographic range are com-parable [1518]. Signals of intermediate duration (0.71.2 s) are common, whereas long signals (more than1.5 s) are rare everywhere. A distinctive feature ofWhite Sea belugas is the higher percent of shortsqueak-like whistles (0.10.3 s), as compared to otherregions. In addition, distinctions are likely to exist inthe frequency characteristics of whistles. Although thegeneralized frequency band of the whistles of belugasfrom the Solovetskii stock is basically similar to thecorresponding frequency bands of belugas from otherpopulations, certain differences are observed betweenthem. Most of the whistles produced by belugas inother points of the areal have a mean fundamental fre-quency of 3 to 7 kHz [1518], whereas belugas in theWhite Sea have a mean fundamental frequency of 2 to4 kHz. In addition, the Solovetskii belugas producealmost no tone signals with a mean fundamental fre-quency of about 5 kHz. At this frequency, we drew aconditional boundary between just whistles (funda-mental frequencies up to 5 kHz) and high-frequencywhistles (fundamental frequencies above 5 kHz). Itshould be noted that, because the energy maximum ofmost of the whistles was shifted from the fundamentalfrequency to one of the higher harmonics, the main sig-nal energy often fell within the frequency band between4 and 8 kHz.

A wavy contour shape was observed for the belugaswhistles in all of the populations studied [1518]. In thepioneering work [15] and in the following studies usingthe same approach to signal classification [16, 18], aspecial contour type corresponding to this modulationpattern was specified: CT6. In the study of the belugasof Alaska [17], where an original scheme of signal cat-egorization was used, a type of whistles (CT8) whosemain distinctive feature was the wavy modulation pat-tern was specified as well. In addition, a series of othertypes possessing the wavy modulation pattern was oneof the important features revealed: for example, a risingwhistle with a wavy frequency modulation (CT3) and awhistle with a weak wavy frequency modulation(CT13). Our data cast some doubt upon the statementthat Solovetskii belugas use tone signals whose mainfeature consists in wavy frequency modulation. Indeed,among the dominant group of signals, i.e., whistles(W), we did not detect any signals of this type. At thesame time, wavy frequency modulation is oftenencountered in both whistles and high-frequency whis-tles [30]. However, in most cases (except for HFWT2[30]), this feature should be considered as a secondaryone manifesting itself in different types of whistlesunder certain conditions (e.g., when the animals are ina state of strong emotional excitation). The appearanceof wavy frequency modulation in the case of strongemotional excitation seems to be a general tendencytypical of different types of signals produced by odon-tocete cetaceans (see, e.g., [3, 32]).

Signals that are most popular with the belugas ofNorth America [1517, 20} and Spitzbergen [18] areflat whistles. In contrast, the major part of signals pro-duced by the belugas in the RG in the White Sea areshort whistles of type W1 (squeak), predominantly,with a V-shaped contour. In addition, a considerablepart of multicomponent whistles of type W2 (chirrup)also consist of V-shaped elements. Thus, the V-shapedcontour is most often encountered in the signals pro-duced by the belugas in the RG in the White Sea.

Another important distinction consists in that trulyflat whistles do not predominate in the vocal productionof White Sea belugas; moreover, these signals are rare(~2%). These animals produce not flat but flattenedwhistles, which are relatively numerous: 7.5% of allcommunicative signals. It should be noted that, sinceflattened whistles are much longer than W1, they alsorequire more time and effort for their emission; how-ever, they still range below the whole set of V-shapedsignals in these parameters.

Considering geographic variability, it is necessary totake into account that the material for this study wasonly collected in the RG. In other situations, signalsproduced by animals may be different [19, 31]. How-ever, we believe that the distinctions revealed by us canstill be attributed to geographic variability, because therecords of the belugas signals obtained at other sites ofthe species geographic range largely refer to similarconditions; i.e., they were obtained in the summer gath-erings of beluga whales [1517, 20].

In total, the repertory of true tonal signals of theWhite Sea belugas is similar to the repertories of thebelugas whistles observed in other populations [1518]. However, certain types (W3, W8, W16, HFWT4,and HFWT10) seem to be unique. In addition, unlikebelugas from other populations, the Solovetskii belugasin the RG most often produce whistles with V-shapedcontours (W1 and W2).

ACKNOWLEDGMENTSThis work was supported by the International Fund

for Animal Welfare. We are grateful to J. Burt (CornellUniversity, US) for the possibility of using the Syrinx2.1 software.

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Translated by E. Golyamina

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