Indicators of age, body size and sex in goat kid calls revealed using the source-filter theory

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Indicators of age, body size and sex in goat kid calls revealed using the source-filter theory
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  See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/230616396 Indicators of age, body size and sex in goat kidcalls revealed using the source-filter theory   Article   in  Applied Animal Behaviour Science · September 2011 DOI: 10.1016/j.applanim.2011.05.012 CITATIONS 25 READS 46 2 authors:Some of the authors of this publication are also working on these related projects: Impact of animal socio-cognitive skills on human-animal interactions: goats and human handlersView projectElodie BrieferETH Zurich 43   PUBLICATIONS   561   CITATIONS   SEE PROFILE Alan G. McElligottQueen Mary, University of London 55   PUBLICATIONS   1,406   CITATIONS   SEE PROFILE All content following this page was uploaded by Alan G. McElligott on 08 January 2017. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the srcinal documentand are linked to publications on ResearchGate, letting you access and read them immediately.  This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institutionand sharing with colleagues.Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third partywebsites are prohibited.In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further informationregarding Elsevier’s archiving and manuscript policies areencouraged to visit:http://www.elsevier.com/copyright  Author's personal copy AppliedAnimalBehaviourScience 133 (2011) 175–185 ContentslistsavailableatScienceDirect Applied   Animal   Behaviour   Science  journalhomepage:www.elsevier.com/locate/applanim Indicators   of    age,   body   size   and   sex   in   goat   kid   calls   revealed   using   thesource–filter   theory Elodie   Briefer ∗ ,   Alan   G.   McElligott ∗∗ QueenMaryUniversityofLondon,SchoolofBiologicalandChemicalSciences,MileEndRoad,LondonE14NS,UK  a   r   t   i   c   l   e   i   n   f   o  Articlehistory: Accepted17May   2011 Available online 15 June 2011 Keywords: Acousticanalysis Caprahircus UngulateVocalcommunicationVocaldevelopment a   b   s   t   r   a   c   t The   source–filter   theory   is   an   important   framework   recently   applied   to   the   study   of    animalvocalisations,   which   links   the   mode   of    vocal   production   to   callparameters.   Vocalisationscan   be   good   indicators   of    asender’s   characteristics,   such   as   identity,   body   size,   age,   andevenhormonal   status   and   affective   states.   For   these   reasons,   applied   vocal   communica-tionresearch   would   greatly   benefit   from   adopting   the   source–filter   theory   approach   toidentifykey   call   parameters   linked   to   physical   and   physiological   characteristics   of    domes-tic   animals.   Here,   we   introduce   the   source–filter   theory   through   adetailed   analysis   andinterpretation   of    goat   contact   calls   during   development.   Inmammals,   vocal   developmentismostly   influenced   by   maturation.   Maturational   processes   of    vocalisations   are   linked   togrowth   or   sex   hormone   effects   on   the   larynx   and   vocal   tract.   We   investigated   changes   totheparameters   of    goat   contact   calls   during   ontogeny,   according   to   age,   bodysize   and   sex.We   recorded   goat   kids   from   birth   to   four   months   old   and   analysed   their   calls   by   consideringthe   shape   and   functioning   of    the   vocal   apparatus.   We   found   age   andsex-related   changestomost   of    the   measured   vocal   parameters,   suggesting   adirect   or   indirect   effect   of    sex   hor-mones   onvocal   ontogeny.   Furthermore,   body   size   growth   was   negatively   correlated   withmostfrequency   parameters,   indicating   that   vocal   production   isconstrained   bybody   sizethroughout   development.   Therefore   kidvocalisations   provide   information   about   age,   sexand   body   size.   We   suggest   that   similar   analyses   applied   to   the   study   of    vocal   correlates   of affective   states,   could   greatly   help   the   discovery   of    convenient   and   non-invasive   indicatorsofanimal   welfare. © 2011 Elsevier B.V. All rights reserved. 1.Introduction Accordingtothesource–filtertheoryofvoiceproduc-tion(Fant,1960),mammal   vocalisationsaregeneratedbyvibrationsofthevocalfolds(“source”)andaresubse-quentlyfilteredbythevocaltract(“filter”).Thisframework,originallydevelopedtostudyhumanspeech(Titze,1994),hasrecentlyprovedveryusefulforanimalvocalcommu-nicationresearchbylinkingvocalproductionmechanisms ∗ Correspondingauthor.Tel.:+442078827420;fax:+442078827732. ∗∗ Correspondingauthor.Tel.:+442078823298;fax:+442089830973. E-mailaddresses: e.briefer@qmul.ac.uk(E.Briefer),a.g.mcelligott@qmul.ac.uk(A.G.McElligott). tocallparameters(TaylorandReby,2010).Source-relatedvocalparametersdependontheanatomy/physiologyofthelarynxandthesub-laryngealandlaryngealstructures(e.g.vocalfoldlengthandmass),whereasfilter-relatedvocalparametersaredeterminedbytheanatomy/physiologyof thesupralaryngealvocaltract(e.g.shapeandlengthofthevocaltract).We   suggestthatthisframeworkcouldgreatlybenefitappliedvocalcommunicationresearchbyidentify-ingkeyvocalparametersandlinkthemtothestructuresof thevocalapparatusofdomesticanimals.Thiswouldallowafarbetterunderstandingofwhyandtowhatextentcallstructurevariesbetweenindividualsandbetweentestedsituations.Thedevelopmentofanimalvocalisationsisinflu-encedbygrowth,maturationandexperience.Mammal 0168-1591/$–seefrontmatter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2011.05.012  Author's personal copy 176  E.Briefer,A.G.McElligott/AppliedAnimalBehaviourScience 133 (2011) 175–185 vocalisations,withfewexceptions( JanikandSlater,1997),arebelievedtobegeneticallydeterminedwithonlylimitedflexibility(SeyfarthandCheney,2010).Changesduringcallontogenyaremainlyattributedtomaturationalprocesses.However,developmentalchangesinvocalproduction(acousticparametersofvocalisations)havemostlybeeninvestigatedinmammalswithcomplexvocalrepertoires(e.g.bats, JonesandRansome,1993;meerkats, Suricatasuricatta ,Hollénetal.,2008;primates,Eyetal.,2007a; seals,KhanandMarkowitz,2006).Othermammalswithlesscomplexrepertoireshavereceivedlittleattention,andknowledgeoftheinfluenceoffactorssuchasgrowthonvocalparametersisweak(e.g.felids,Peters,2011).Changesinvocalisationsduringdevelopmentcanbelinkedtogrowthandsex-relatedhormonalchanges.Thelarynxisasteroidreceptortargetorgan(Aufdemorteetal.,1993),andtherefore,source-relatedvocalparameterscanbeaffectedduringdevelopmentbychangesintestosteronelevelsorbygrowth-relatedlengtheningofthevocalfolds(TaylorandReby,2010).Thevocaltractgrowswiththerestofthebodyanditslengthisdirectlydependentonbodysize(TaylorandReby,2010).Becauseofthenega-tiverelationshipbetweenfrequencyparametersandbodysize(orweight)amongadultindividualsinseveralspecies (RebyandMcComb,2003;VannoniandMcElligott,2008),thesamenegativecorrelationisexpectedforjuvenilesdur-inggrowth(Peters,2011).Filter-relatedvocalparametersshouldthuschangeduringdevelopment,withbodysize-relatedlengtheningandwideningofthevocaltract.Thephysicalandphysiologicalcharacteristicsofani-malsarestronglylinkedtothevocalisationstheyproduce(TaylorandReby,2010).Forthesereasons,various vocalparametershaveproventobegoodindicatorsof calleridentity(VannoniandMcElligott,2007;Brieferand McElligott,inpress),quality(Rebyetal.,2005;Brieferetal., 2010)andevenhormonalstatus(Charltonetal.,2010). Vocalisationscouldalsobereliableindicatorsofinnerstates(Gogolevaetal.,2010).Indeed,emotionsareasso- ciatedwithphysiologicalandneurologicalchangesthataffectrespiration,salivationandtensionofthevocalfoldsandvocaltractwalls,causingmodificationsofthevocalparameters(Scherer,1986).Thereforevocalparametersarepromisingnon-invasivetoolstoassessanimalwelfare(WearyandFraser,1995;Manteuffeletal.,2004).However,inordertofindvocalindicatorsofaffectivestates,agoodunderstandingofthevocalproductionmechanismsandthewayemotionsinfluencevocalproductionisrequired.Moreimportantly,athoroughknowledgeofthestructureofvocalisationsproducedinlow-affectsituations(e.g.con-tactcallsproducedatclosedistance)ateverystepofvocalontogenyiscrucialinordertodetectthesubtlevaria-tionsinstructurethatindicatedifferentinnerstates.Inthisstudy,weintroducethesource–filtertheorythroughadetailedanalysisandinterpretationofgoatcontactcallsduringontogeny.Weinvestigatedchangesduringdevelopmentinvocalcharacteristicsaccordingtoage,bodysizeandsexinahighlyvocallivestockspecies,thegoat( Caprahircus ).   Inthishighlysocialandvocalspecies,anexclusivebondingbetweenthemotherandtheneonateisdevelopedwithinafewhourspostpartum(Poindronetal.,1993;Miranda-delaLamaandMattiello,2010).Asaconsequence,mutualmother–kidvocalrecognitionisevidentfromthefirstweekpostpartum,andthisrecognitionprobablyreliesontheindividualcharacteristicsofthecalls(BrieferandMcElligott,inpress).Here,we   studiedage-relatedchangesaccordingtosexinbothsource-andfilter-relatedvocalparameters,aswellasintensityparameters,frombirthtofourmonthsofage.We   alsoinvestigatebodysize-relatedchangesinvocalisations.We   predictedthatmostvocalparameterswouldchangewithageasaresultofbodygrowth,andthatthesechangeswouldbesex-dependent. 2.Methods  2.1.Subjectsandmanagementconditions ThestudywascarriedoutatWhitePostFarm,Notting-hamshire(53 ◦ 06  N,1 ◦ 03  W),   UK,onfourgroupsofpygmygoatkidsborninJuly2009,December2009,March2010andJuly2010,respectively( n =23;5femalesand18males;mean ± SEgroupsize=5.8 ± 0.5kids).Allkidshadthesamefather(i.e.theywereeitherfullorhalfsiblings)andcon-sistedoffoursingleborn,eightpairsoftwinsandonesetoftriplets.Thegoatsusedinthisstudywerekeptindoorsinacom-munalpenof4.4m × 4.5m.   Whenafemalewasabouttogivebirth,shewasisolatedina2.5m 2 penwithinthecom-munalpenandkepttherewithherkid(s)for2–3daystoallowadequatedevelopmentofthemother–offspringrelationshipandpreventinterferencefromothergoats.Mothersandkidswerethenreleasedinthecommunalpenwiththeothergoats.At2–3monthspostpartum,allthegoats(mothersandkidstogether)weremovedtoabig-gerpenwithotherindividuals.Malekidswerecastratedbyusingaconstrictiverubberringappliedtotheneckof thescrotum3–4daysafterbirth(usualprocedureinUK;DEFRA,2009).Thiswascarriedoutaspartofroutineman-agementoftheanimalsbytheowners.  2.2.Recordingsandselectionofcalls Goatsproducetwo   kindsofcallswhenisolated,accord-ingtothedegreeofstressofthesituation.“Contactcalls”arethemostcommon,andareusedtomaintaincon-tactwithothergoatswhenphysically,butnotvocallyseparated,whereas“distresscalls”arehigh-pitched,andassociatedwithhighstresslevels(Lenhardt,1977).Inotherspecies,distresscallshavebeenshowntogenerallylackusefulinformationsuchasindividualidentity,oratleasttocontainlessinformationthancontactcalls(e.g.reddeer, Cervuselaphus ,   VankováandMálek,1997;chacmababoons, Papioursinus ,   Rendalletal.,2009).Becausewe   wereinterestedinlow-affectvocalisationspotentiallyencod-inginformationaboutage,bodysizeandsex,we   focussedinthisstudyoncontactcalls.We   recordedgoatkidcon-tactcallsatdistancesof1–5mfromthevocalisinganimalusingaSennheiserMKH70directionalmicrophone,con-nectedtoaMarantzPMD660numericrecorder(samplingrate:44.1kHz)between10:00and17:00h.Kidswererecordeddailyduringtheirfirstweek(0–10daysold),atapproximately5weeksold(27–41daysold),andat  Author's personal copy E.Briefer,A.G.McElligott/AppliedAnimalBehaviourScience 133 (2011) 175–185 177 approximately3or4monthsold(104–124daysold)forfourkids(onefemaleandthreemales)thathadbeenkeptatthefarmwiththeirmothers(daysofrecordingperindividual,mean ± SE=9.70 ± 0.38,range=6–14).Thiswasdonebyseparatingkidsduringnomorethan5min,2–3timesperdayatvisualandhearingrange(1–10m)fromtheirmothers.Thedistancetothemotherwas   setat1monaverageduringthefirstdayofrecordingsandincreasedafterwardsifnecessary,untilweobtainedcon-tactcalls(i.e.low-affectvocalisations)andnodistresscalls(seeSupplementaryMaterial).Kidswereisolatedalone,exceptiftheywerestressedduringisolationevenat1m.Inthesecases,theywereisolatedwiththeirsibling(s).Vocalisationswereimportedintoacomputeratasam-plingrateof44.1kHzandsavedinWAV   formatat16-bitamplituderesolution.We   usedPraatv.5.0.47DSPPackage(BoersmaandWeenink,2009)andSeewave(Sueuretal., 2008)forsubsequentanalyses.CallswerevisualisedonspectrogramsinPraat(FFTmethod,windowlength=0.01s,timesteps=1000,frequencysteps=250,Gaussianwindowshape,dynamicrange=50dB).Toassessage,sexandbodysizeeffectsonkidcalls,weselectedeightgoodqualitycalls(lowlevelsofback-groundnoiseasvisualisedonaspectrogram)perkidperdayforsubsequentanalyses(total=1784callsfrom23kids,mean ± SEperkid=77.58 ± 3.04calls).Selectedcallswereseparatedbyatleastthreecallswithinagivenrecordedbout.Thisisimportantinordertoavoidpseudoreplication,becauseconsecutivecallsaremorelikelytobehomoge-neous(Rebyetal.,1999).We   stronglyrecommendthisapproachforotherstudiesofvocalisations.  2.3.Acousticalanalysis Goatcallsareshort,withaclearharmonicstructureandstrongfrequencyandamplitudemodulations(Fig.1).Weextractedsource-related(fundamentalfrequency,“F)andfilter-related(amplifiedfrequencies,“formants”)vocalparametersaswellasintensitymeasuresusingacus-tombuiltprograminPraat.Thisprogrambatchprocessedtheediting,thesettingofparameters,theanalysesandtheexportingofoutputdata(RebyandMcComb,2003;Charltonetal.,2009a).   ThevocalparametersthatwemeasuredarelistedinTable1anddetailedinthe nextparagraphsbelow(Praatcommandsareindicatedinbrackets).Goatsproducetwokindsofcontactcalls:closed-mouthcontactcallsandopen-mouthcontactcalls(Ruiz-Mirandaetal.,1993).Theextentofmouthopen-inginfluencestheresonantpropertiesofthevocaltract(Titze,1994).Severalvocalparametersthusdifferbetweenclosed-andopen-mouthcalls(Sèbeetal.,2010),espe- ciallythefrequenciesandamplitudelevelsofformants.Becausesomeformantsaresuppressedinclosed-mouthcalls,onlykidcontactcallsemittedwiththemouthopen,inwhichformantsaremoreevident,wereusedinthisstudy.Source-relatedvocalparametersweremeasuredbyextractingtheF0contourofeachcallusingacross-correlationmethod([Sound:ToPitch(cc)command],0–10daysold:timestep=0.005s,pitchfloor=300–400Hz,pitchceiling=700–900Hz;27–41daysold:timestep=0.005–0.015s,pitchfloor=200–300Hz,pitchceil-ing=700–800Hz;104–124daysold:timestep=0.015s,pitchfloor=100–200Hz,pitchceiling=600–800Hz).If theentireF0contourcouldnotbedetectedbythecross-correlationmethod,callswerehigh-passfilteredbeforetheanalysis(cut-offfrequency:0–10daysold,300Hz;27–41daysold,200Hz;104–124daysold,100Hz).ThefrequencyvalueofF0atthestart(F0Start)andattheend(F0End)ofthecall;themean(F0Mean),minimum(F0Min)andmaximum(F0Max)F0frequencyvaluesacrossthecall;thepercentageofthetotalcalldurationwhenF0wasmaximum(TimeF0Max);andtheF0meanabsoluteslope(F0AbsSlope)wereincludedinouranalyses.TocharacteriseF0variationalongthecall,wemeasuredthemeanF0variationpersecond(F0var),calculatedasthecumulativevariationintheF0contourinHertzdividedbycallduration.We   alsomeasuredthenumberofcompletecyclesofF0modulationpersecond(FMRate)andthemeanpeak-to-peakvariationofeachF0modu-lation(FMExtent,seeCharltonetal.,2009a).   Finally,weincludedtwo   othermeasuresofF0variation:jitter(Jitter,Titzeetal.,1987),whichisthemeanabsolutedifferencebetweenfrequenciesofconsecutiveF0periodsdividedbythemeanfrequencyofF0[Jitter(local)command];andshimmer(Shimmer),whichisthemeanabsolutediffer-encebetweentheamplitudesofconsecutiveF0periodsdividedbythemeanamplitudeofF0[Shimmer(local)command].Filter-related(formants)vocalparametersweremeasuredbyextractingthecontourofthefirstfourformantsofeachcallusingLinearPredictiveCodinganalysis(LPC[Sound:ToFormant(burg)command],0–10daysold:timestep=0.003s,maximumnumberof formants=4–5,maximumformant=9800–12,000Hz,windowlength=0.01–0.04s;27–41daysold:timestep=0.01–0.025s,maximumnumberoffor-mants=4–5,maximumformant=8000–10,000Hz,windowlength=0.01–0.05s;104–124daysold:timestep=0.025s,maximumnumberofformants=4–5,max-imumformant=5000–7000Hz,windowlength=0.05s).WecomparedtheoutputsoftheLPCanalysiswithvisualinspectionsofspectrogramstocheckifPraataccuratelytrackedtheformants.Spuriousvaluesandinter-segmentvalues(seeFig.1)weredeletedandwecorrectedforoctave jumpswhennecessary.We   includedinouranalysesthemean(F1–4Mean)minimum(F1–4Min),andmaximum(F1–4Max)valuesoftheformants.We   thenestimatedtheminimumspacingoftheformants(DfMin),knownasminimumformantdispersion,usingthemethoddescribedbyRebyandMcComb(2003).   Additionally,weincludedinouranalysesthefrequencyvaluesattheupperlimitofthefirst(Q25%),second(Q50%)andthird(Q75%)quartilesof energy,measuredonalinearamplitudespectrumappliedtothewholecall.We   measuredintensitycharacteristicsbyextractingtheintensitycontourofeachcall[Sound:ToIntensitycommand].We   thenincludedinouranalysesthemeanvariationpersecond(AmpVar),calculatedasthecumu-lativevariationinamplitudedividedbythetotalcallduration;thenumberofcompletecyclesofamplitudemodulationpersecond(AMRate);andthemeanpeak-to-
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