AquaticMammals 2003, 29.2, 177–180
Pinniped vocalcommunication: an introduction
Ronald J.Schusterman 1 andSo e M.VanParijs 2
1LongMarine Laboratory, University of CaliforniaSanta Cruz, Santa Cruz, California, 95060, USA 2Institutefor Aquatic Biology, Norwegian College of FisheriesScience, University of Tromsø, Tromsø, Norway
Communicationforms the fabric of animalsocial life . ..infact, looking at the way in which animals spend their time,it is striking how much of it they spend either in uencing, or being in uenced by, the behavior of other animals—inother words, in some form of communication. —Dawkins,Unraveling Animal Behavior, p. 71
Thepinnipeds evolved and diverged tens of millions otherdescriptors. The variability in pinniped vocal ofyears ago and spread throughout the oceans of signallingcan be assessed at the level of theindivid- theworld, colonizing isolated shores and feeding ual,as well asby age and gender class, emotive innearby productive waters. While the thirty-three state,geographic location, and species, and the livingspecies of seals, sea lions, and walruses diVerencesdocumented thus far re ect a degreeof inhabitunique behavioural and ecological niches, adaptationin vocal signalling that is rare among onesigni cant commonality amongst these animals mammals.The acoustic characteristics of the sig- isthe apparent structural complexity of theirvocal- nalsproduced by pinnepeds are well-designed to izationsand the degree to which they use these gainthe attention of conspeci cs— incidentally, vocalizationsin communicative contexts. Some thesesounds have also captured the interest and species,including the sea lions and some land- imaginationof humanlisteners. breedingseals, congregate seasonally on crowded Forcenturies, seals have been signi cant in the rookerieswhere the repetitive calls of thousands of culturesof people living in close proximity to them. individualsswell into an incessant din. Other Notsurprisingly, many of the legends and stories species,including most of the aquatically breeding featuringthese animals are concerned with their seals,appear more reserved on their haul-outs, vocalcommunication. In these stories, seals may rarelyproducing audible sounds except for the takeon humanform, talk and sing with people and occasionalguttural threats of adults and the bleats withone another, and give warning of impending ofdependent pups. Many of theseaquatic breeders disaster(Maxwell, 1967; Thomson, 1914/ 1965). wereonce thought to be relatively silent, but Manyof these observations have been published as accumulatingobservations have shown them to factualaccounts. For example, Maxwell (1967) haveunusual and complex underwater vocal reper- refersto a 1920’s newspaperarticle which states toires.Among the pinnipeds, the walruses are that ‘...thereis undoubtedtestimony that the great themost amphibious callers of all, producing fre- greyseals of the Atlantic who visit the islands have quentand assorted aerial and underwater sounds. beenheard singing— for no other word applies to Intriguingly,all pinnipeds appear capable of sound theirvery human voices. ’Manyyears later, a ‘talk- productionon land and in water, and some even ing’harbour seal named Hoover at the New emitcalls simultaneously above and below the EnglandAquarium rekindled the notion that seals water’s surface. couldlearn to speak (Ralls, et al., 1985). Inaddition to the quantity of vocalizations emit- Inthe 1960’ s, scienti c explorationof pinniped tedby pinnipeds is the surprising diversity of the vocalcommunication began in earnest, led by soundsthemselves, which have been categorized ahandfulof dedicated American investigators, bylisteners as clicks, creaks, bleats, growls, barks, includingThomas Poulter, Bill Scheville,Carlton whinnies,buzzes, grunts, snorts, songs, pulses, trills, Ray,Burney Le Bouef,Dick Peterson, Nicholas thumps,blasts, groans, sirens, sweeps, yelps, roars, Collias,George Bartholomew, Ian Stirling, and one hums,chirps, belches, squeals, bells, whistles, ofthe editors of thisissue [RJS]. This early research knocks,mews, chucks, glugs, coos, gongs, clacks, tendedto emphasize structural descriptions of claps,drones, trumpets, whimpers, pu Vs, burps, aerialand underwater sounds emitted by readily snarls,hisses, warbles, moans, and bellows, among accessiblesea lions, fur seals, and elephant seals. In
? 2003 EAAM 178 R.J.Schustermanand S. M.VanParijs additionto recording and describing vocalizations, largelybecause of thebringing together of con ict- thesescientists attempted to establish hypotheses ingterms along with con icting de nitions and regardingthe use of these sounds in socially unworkablemetaphors. These de nitionsand meta- communicativecontexts, as well asin auto- phorsare largely unworkable because of con icts communicativecontexts, namely foraging and navi- betweengroup selectionist and sel sh-genetheory gationvia echolocation. Over the next 40 years,the viewsof communication. While ethologists and possibilityof pinniped echolocation diminished as psychologistsgenerally consider communication, observationsand experiments on their sensory sys- alongwith other aspects of social behaviour, in a temsand their underwater-emitted sounds revealed Darwinianevolutionary framework, many investi- thatspecialized echolocation abilities were lacking gatorsstill opt to describe communication among inmost if not all species (Schusterman et al. 2000). animalsas involving the cooperative sharing of However,ideas about the social functions of their information. vocalizationswere transformed into eld and lab Thisnotion, as described by W. J.Smith(1977), investigationsas moreinformation about the vocal hashad strong support among workers in the eld behaviourof various species began to accumulate. ofmarine mammalogy (Miller, 1991; Tyack & These eVortswere later elevated and expanded by Miller,2002; Dudzinski et al.,2002).From our theadvent of new recording technologies and im- pointof view, the greatest di Ycultythat such an provedgeographic accessibility, which facilitated information-transfermodel has is the confusing of theacoustic monitoring of animalsdiving, foraging, theseparable roles and tnessinterests of signallers andsocializing at sea. andperceivers. For example, in a recentencyclo- Presently,we knowsomething about the vocal paedicreview of communication in marine mam- repertoiresof over three-quarters of pinniped mals,Dudzinski et al.2002state that during an species,including terrestrial and aquatic breeders, exchangeof information, both sender and receiver andpolar, temperate, and tropical species. Early dependon the ‘accurateinterpretation of signalsto researchershave trained and stimulated new meetcommon group challenges such as repro- generationsof scientists, and these investigators duction,predator defense, foraging, and parental continueto re ne,increase, and synthesize our care’ (p.249). The authors also go on to say that understandingof the relationship between sound communicationamong marine mammals promotes productionand behavioural ecology in pinnipeds. groupcohesiveness. It is di Ycultto reconcile such At thestart of the new millennium, researchers aviewof communication with an evolutionary representingseveral generations met at the 2001 approach.According to Darwinian evolution, a meetingof the Society for Marine Mammalogy, in communicativeact should be bene cial to the Vancouver,Canada, to participate in a special sender,but not necessarily the receiver (this is symposiumorganized by the guest editors of particularlytrue of con ictsituations or contests thisissue [SVP and RJS]. This issue of Aquatic overresources where there is often a costincurred Mammals isthe result of that symposium, with bythe receiver). In addition, a Darwinianapproach contributorsincluding the speakers at that meet- suggeststhat communicative acts provide indirect ingand others working on original research in bene tsto receivers only when signals function to the eld. contributeto the welfare of kin, or as part of Followingthe Vancouver symposium in 2001, reciprocatedaltruism occurring among non-kin andour decision to co-edit this volume, we had (Trivers,1985). avarietyof discussions with one another, the Approachinganimal communication, particu- contributors,reviewers, and our colleagues about larlyvocal communication, without using con- pinnipedvocal communication. The topics of structsgleaned from information transfer theory, theseinteractions ranged from editorial issues to Owings& Morton(1998) and Owren &Rendall technologygaps to philosophical points of view. (1997)have taken a similarapproach to dis- Betweenus, one issue about animal communication entanglingthe roles of sender and receiver in emergedas particularly controversial and signi - evolutionary-basedmodels of communication. cant,and we wouldlike to brie youtlineit in this Basically,these theoreticians suggest that vocal introduction. communicationis a re ectionof the fundamental processof signallers regulating the behaviour of Thequote underscoring the importance of com- receivers,and receivers assessing the characteristics municationthat appears at the start of this intro- ofsignallers. From this sel sh-geneperspective, ductionappears in a textbookon animalbehaviour signallerscontrol the behaviour of receiversto their byMarian Stamp Dawkins (1995). In this text, own bene t,and not necessarily to the bene t of Dawkinspoints out that, despite intensive study listeners.Perceivers, on the other hand, receive the andthoughtful theory, the whole subject of animal signaland respond or notdepending on whether or communicationis nevertheless extremely confused, notthey receive a bene tfordoing so. Thus, Pinnipedvocal communication 179 signallingand perceiving can be viewed as serving Thecollection of papers included in this volume independentself interests. representsa signi cantstep forward in the research Ina complementaryevolutionary analysis of areaof pinniped vocal communication. The con- vocalcommunication, Morton ’smotivation- tributedarticles are either reviews of speci c sub- structuralprinciples of vocal communication topicsin the eldor empirical studies of vocal (1977),which have been previously applied to ter- communicationin individual pinniped species. restrialmammals and birds, can readily be applied Theydraw from a fairlydiverse group of scholars, topinnipeds. For example, the raucous sounds allof whom have placed their work within an comingfrom terrestrial breeding grounds are gen- ecological/evolutionarycontext, sometimes with a erallyloud, directional, often broadband, and are heavyemphasis on how pinniped life-history pat- alwayshighly repetitive. These signals are well- terns,such as the movement and distribution designedto attract a listener ’sattention.Morton ’s ofindividuals, maternal strategies, reproductive ideasabout how a Vectrelates to the structural physiologyand behaviour, breeding habitat, componentsof acoustic signals can be seen in the foraging,and predation —aswell asontogenetic lowfrequency, broadband, sharp-onset calls emit- factors—in uencethe form and function of vocal tedby pinnipeds in aggressive contexts and their communication.Sexual selection is also a major higher-frequencywhine and bleat-like calls that are themein several of the papers. These papers deal emitted in aYliativecontexts. Thus, for example, in withthe structure and function of thevocal displays thecontext of sexual selection, because larger indi- producedby males of aquatically mating pinniped vidualswin aggressive physical contests among speciesin the context of examining how acoustic- maleswanting access to females, selection favours displaybehaviour may function in lek breeding harshroar- and growl-like qualities that re ect situations,where individuals are likely to be evalu- bodysize. In this manner, vocal communication ating the tnessof others on the basis of vocal mayserve to replace ghtingbecause such acoustic signals.Perhaps the most exciting aspect of the signalscan substitute for body size as an indicator reviewscontributed on the role of acoustic signal- ofresource holding potential (Owings and Morton, lingin individual recognition and social systems is 1998).This type of communicationhas beentermed thefresh comparative approach taken by the inves- ‘expressivesize symbolism ’,orESS, because, tigators.The new synthetic ideas and viewpoints accordingto evolutionary game theory, it is an containedin these articles arise from the accumu- ‘evolutionarystable strategy ’. latingbody of descriptiveacoustic and behavioural datathat is now available for a considerable Inthis brief introduction, we haveattempted to numberof pinniped species. highlightwhat we considerto be one of the major As thepapers in this volume illustrate, we problemareas in the study of animal vocal com- haveclearly moved beyond the anthropomorphic, municationin general and pinniped vocal com- anecdotalapproach to the study of vocalcommuni- municationin particular, namely, the importance of cationin pinnipeds, and collectively, we aremaking usingan inclusive de nitionof communication, steadyprogress towards achieving a highlevel whichplaces equal emphasis on regulation of the ofaccurate, objective, cogent, and comparative signalon the part of the sender and assessment of descriptionsof pinniped vocal behaviour. Future thesignal on the part of the receiver. Our current studies,which aim to encompasswell-de ned etho- understandingof pinniped vocal communication, logical,ecological, and evolutionary concepts deal- thatis, the relationship between sound production ingwith communication in these animals, await us. andbehaviour, has been bolstered by anincreasing numberof studies and internationally published Acknowledgments literature(see recent reviews in Tyack, 1999, and Tyack& Miller,2002). In order to build on this We aregrateful to Jeanette Thomas, editor of foundation,Tyack & Miller(2002) have suggested AquaticMammals ,forencouraging us to take on thatthe areas presenting the greatest opportunities thechallenge of assembling this issue. It hasbeen a forfuture research on the proximate and ultimate rewardingexperience that has brought us closer to causesof pinniped acoustic communication include oneanother, our growing science, and our col- acousticperception and categorization, functional leagues.We thankthe contributors for their hard analysesof vocal behaviour, the behavioural sig- workand their patience throughout a rigorous ni canceof the variation in acoustic displays, and editorialprocess, and we arelikewise indebted to vocaldevelopment and vocal learning. It appears thosewho served as reviewers,for their detailed and tous that all of these areas can be approached insightfulevaluations. We wouldespecially like to fromthe standpoint of the signallers and receivers, thankPeter Corkeron, Colleen Reichmuth Kastak, andtheir sometimes con ictingand sometimes andBrandon Southall, whose e Vortshelped make coincidinginterests. thisvolume possible. 180 R.J.Schustermanand S. M.VanParijs
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