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AjuvenileMacrochelys temminckii(alsoillustratedinFig.2)baskingonafloatingrailroadtieat0727h.notetheleechoccupyingaspacebetweenthevertebralandrightlateralkeels.
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basking in the alligator snapping Turtle, Macrochelys temminckii (Testudines:
chelydridae)Johnl.Carr1,samuelR.holcomb1,2,andmitchellJ.Ray1,3
1Departmentofbiologyandmuseumofnaturalhistory,Universityoflouisianaatmonroemonroe,louisiana71209,UsA([email protected])
2louisianaDepartmentofWildlifeandFisheries,p.o.box98000,batonRouge,louisiana70898,UsA([email protected])33321bluebirdRidge,newbraunfels,texas78130,UsA([email protected])
photographsbytheseniorauthor.
macrochelys temminckii is the largest freshwater turtle in northAmerica,andisoftenconsideredoneofthemostaquaticspecies
aswell(pritchard1967).onlyadultfemalesareknowntoregularlyleavethewater,andthenonlytonest(ernstandbarbour1972,Zappalorti1976,pritchard1989).baskinginthisspecieswaslongthoughttobenon-existentorextremelyrare(brattstromandCollins1972,ernstandbarbour1972).Althoughsomeauthorshavesuggestedthataquaticbask-ingoccursinthisspecies(Zappalorti1976,howeyandDinkelacker2009),nopublishedreportsdescribesuchbehavior.however,severalpublicationsdescribeaerialbaskinginM. temminckii,buteachliteraturereportcon-sistsofasingleobservation(ewert1976,shelbyandJensen2002,Farretal.2005,selmanetal.2009,thomas2009,selmanandWillig2010).ofthesixreportedinstancesofbasking,onewasahatchling(42mm,shelbyandJensen2002),threewerejuveniles(~100–200mmCl;ewert1976,thomas2009,selmanandWillig2010),andtwowereofadultsizes(~350–400mm,Farretal2005;~400–500mm,selmanetal.2009).oneinstanceofbaskingwasinferredfromcapturingaspecimeninabaskingtrap(shelbyandJensen2002).Intheotherfivecasesinwhichbaskingwasactuallyobserved,threeoftheturtlesappearedtohavebeenbaskingforsometime,astheanimalsweredescribedasdry(ewert1976,Farretal.2005,thomas2009),butthemaximumreportedobservationperiodlastednolongerthanabout12min(Farretal.2005).Allsixobservationswereassociatedwithlotichabitats(creeksorrivers),withbaskingsubstratesincludingafallentreetrunk,snags,andriverbanks.Wherereported,turtleswererestingonthebaskingsubstrateinclinedatanglesestimatedat30–60°,withtheheadpointedupslope(ewert1976,Farretal.2005,selmanetal.2009).Inonecase,theanimal’srestinganglewasnotnoted,butthesnagtoascendtothebaskingspotwasnearlyvertical(90°)andinvolvedclimbingoveraninterveningobstacle(selmanandWillig2010).thefiverecordedtimesforbaskingbehaviorwerebetween1000and1700h. Duringthe2009fieldseason,weobservedtwoinstancesofaerialbaskingandoneofaquaticbasking,allinvolvingjuvenileM. temminckii.observationsweremadeatblackbayoulakenationalWildlifeRefuge,11.5kmnorthofmonroeinouachitaparish,louisiana.thecenterpieceoftherefugeisalargelake(~845ha),whichisabackswamp(Wang1950)thathasbeendammedbyarailroadline,andnowhasthewaterlevelcon-trolledwithastop-logstructure.Airtemperatureswereobtainedfromtheneareststationinouachitaparishfortheappropriatedateandtime(WeatherUnderground,http://www.wunderground.com). Whileradio-trackingonblackbayoulakeatapproximately1400hon9march2009,ajuvenileM.temminckii(carapacelength[Cl]=174.3mm,weight=1.04kg)wasobservedwithitsheadexposedabovethewater.theafternoonwassunny,withverylittlecloudcover.Uponcloserinspec-tion,theturtlewasfoundtobefloatingaboveabedofsubmergedaquatic
vegetationcomposedprimarilyofEgeria densa (brazilianWaterweed) andCeratophyllum demersum (Coontail).theheadandkeelsofthecarapacewereexposedabovethewater,whereitremainedforaperiodof~5min,withnoindicationthatitwasforaging.theturtlewascapturedbyhandandbroughttothelabforexamination.ItwasidentifiedbyapIttagasa“head-started”juvenilefromthe2004year-classthatwereleasedon12June2008.Watertemperatureatthetimeofcapturewas21°Candairtemperaturewasapproximately27°C.thisobservationmatcheswellthe
AllIGAtoRsnAppInGtURtles
Fig. 1.JuvenileMacrochelys temminckii(A)baskingontheendofarailroadtieintheshadeofaWaterelm(Planera aquatica).thesameindividual(b)immediatelyaftercapture.notethelargeleechattachedtothecarapace.
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descriptionofaquaticbaskingbymollandlegler(1971).theydescribedaquaticbaskingasbehaviorinwhich“turtles...weremotionlessatthesur-facewithlimbsfullyextendedandpartofthecarapaceoutofthewater,”andwentontosaythatthemostcommonsitesforaquaticbaskingofpanamaniansliders(Trachemys venusta)“wereoverbedsof[asubmergedaquaticplant]ornearothermatsofvegetation.” Inthecourseofterrestrialnestingsurveysalongtherailroadcausewayinthenorthwesterncornerofthelake,weobservedajuvenile(Cl=190.2mm,weight=1.52kg)on20April2009at0900h.Itwasrestingonanoldrailroadtieamongriprapatthemarginofthelake,29cmabovegroundlevel.thewetturtlewassittingaskewonthebankendoftherailroadtiewithalargeleechontherightsideofitscarapace(Fig.1).therailroadtiewasinclinedat~12°intothewaterfromthebank.basedontheanimal’spositionandthewettrailitleftonthetie,theturtlehadtohaveclimbedthebankandthentheendoftherailroadtie(~80–90°)toreachitsloca-tionatopthehigh,out-of-waterend.theturtlewaspositionedinsuchawaythatitwasrestingatananglenearhorizontal.thelefthindlegwasdanglingintheair,buttheright-sidelimbswereextendedandincontactwiththesubstrate;theheadandneckwerealsoextendedandrestingonthewood.thedigitswerenotmaximallyabducted(spreadapart).thisturtlewasobservedforjustafewminutesbeforebeingcaptured.Whenapproached,theanimalquicklydoveintothewateronthelake-sideoftherailroadtie.Atthetimeofthisobservationconditionswereclearandsunny,althoughthebaskingsitewasfullyshadedbyasmallWaterelm(Planera aquatica).Airtemperatureatthetimeofcapturewasapproximately17°C. WefoundanotherbaskingM. temminckiiduringaterrestrialnestingsurveyalongthelakemarginon29April2009.At0720h,ajuvenile(cara-
pacelength~140mm)wasobservedonarailroadtiefloating~3mfromtheshoreline(Fig.2).Ascanbeseeninthephotograph,thetailextendsstraightbehindthebody,therighthindlegisminimallyextendedwithoutabducteddigits,therightforelimbismorefullyextended,andallareincontactwiththesubstrate.theheadandneckarefullyextendedandtheanimalappearsalert,possiblywiththeproximalportionoftheneckrestingonthesubstrate.theweatheredrailroadtiewashorizontal,providinga0°baskingsurface,andwaslocatedintheearlymorningshadows,notexposedtothesun.Aleechwasnotedonthecarapace,andtheturtlewasphoto-graphedandobserveduntil0730h,atwhichtimetheobserver(JlC)leftthesite.Atapproximately0807h,whentheobserverreturnedtothebask-ingsite,theindividualwasseeninthesameposition,andthecarapacewasdrier,indicatingthatbaskinghadcontinuedinthemeantime.Inaddition,theleechthathadbeenobservedonthecarapacemoveduntilitwasoutofsight(Fig.2insert),whichfitswiththeideathatthedryingofaturtledur-ingbaskingwouldtendtocauseleechestoreleasetheirhold(pope1939,Cagle1950).theemptypupariumandanewlyemergedadultdamselfly(odonata:Zygoptera)arealsovisibleinoneofourphotos,sotheturtlehadremainedinthesamepositionlongenoughtoserveasasubstrateforemer-gencebythisaquaticinsect.thefirsttolastobservationsofthisindividualspanned58min.Airtemperaturewasapproximately22°C. ourobservationsincludethefirstspecificinstanceofaquaticbask-ingreportedforthespecies,andtwoadditionalinstancesofaerialbask-ing.obbardandbrooks(1979)notedapreponderanceofaerialbaskinginChelydra,buttheincidenceofaquaticbaskingwasashighas16%ofallbaskingobservationsforradio-telemeteredindividualsintheirpopulation.thesearetheonlyobservationsofbaskingM. temminckiithatwehave
Fig. 2.AsecondjuvenileMacrochelys temminckiibaskingonafloatingrailroadtie.notethattheleechismovingacrossthevertebralkeelat0816h.Intheinsert,theleechisnolongervisibleonthecarapaceat0817h.
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madeduring15yearsoffieldworkatthissitebytheseniorauthor(1996–2010),soweareinclinedtoagreewiththenotionthatbaskingoccursonlyrarelyinthisspecies(ewert1976).obbardandbrooks(1979)notedamongthereasonsthatbaskingmighthavebeeninfrequentlyreportedinChelydra serpentinapriortotheirstudywasthatindividualsalmostalwaysbaskaloneonaparticularobject,asopposedtoemydids,whicharefre-quentlyfoundinlargenumbersonthesameobjectorevenstackedononeanother.AllreportsofaerialbaskingMacrochelysareofsingleindividuals,thusiftheanimalsarewary,anindividualcouldveryeasilyslipintothewaterunnoticed.Inaddition,withrespecttoM.temminckii,thedarkcol-orationofthecarapaceandsoftpartswouldtendtobewellcamouflagedonmostlogsorotherwoodystructures,andtheroughtextureoftheshellandsoftpartswouldtendtodisrupttheoutlineoftheturtle,bothofwhichwouldcomplicateseeinganindividualbeforeitslippedintothewater. AllreportsofaerialbaskinginM. temminckiiinvolvesingleindi-vidualsonabankorwoodsubstrate.InC. serpentina(itsclosestnorthAmericanrelative),obbardandbrooks(1979)reportedthat99%of233aerialbaskingobservationsinvolvedasingleturtleonabaskingobject.thepostureassumedbythetwoaerialbaskingM. temminckiithatweobservedwassimilartowhatewert(1976)describedforChelydra,inwhichthefeetremainincontactwiththebaskingobject,ratherthanbeingfullyextendedinmid-airwiththedigitsmaximallyabductedasiscommonlyseenwiththehindlimbsinemydids(Cagle1950,Auth1975).obbardandbrooks(1979)reportedseeinglimbsextendedwiththewebbingspreadinChelydra, buttheydidnotquantifytheincidenceofthebehavior;however,intheirphoto,thelefthindlimbisnotelevatedabovethesubstratewiththedigitsmaximallyabducted.obbardandbrooks(1979)alsonotedthatonlyabout5%oftheirChelydrabaskingobservationsinvolvedanon-shorebaskingsubstrate.WithrespecttoMacrochelys,fouroftheaerialbaskingobservationshaveinvolvedbaskingsubstratesonthebankoralogattachedtothebank,andfourinvolvedfree-floatingorfixedoffshoreobjects. Withatotalofninebaskingobservationsforthespeciesnow,com-parisonwithfactorsrelatedtotheappearanceofthebehaviormaystarttobemade.someexplanationsforbaskingareapplicableonlytoadultturtles.ofthenineknowninstancesofbaskinginM. temminckii,themajorityofindividualswerejuveniles(7of9,includingour3observations),soanyassociationwithmaturationofovarianfolliclesinfemalesorwarmingbybaskinginthespringtoenhancematingbehavior(obbardandbrooks1979)couldaccountfornomorethanasmallfractionofthereportedcases.Anumberofgeneralexplanationsforbaskingbehaviorareavailable,includingthermoregulation(boyer1965,mollandlegler1971,obbardandbrooks1979),vitamin-Dsynthesis(pritchardandGreenhood1968),dryingoftheskinandshellsurfacethatcouldreduceectoparasiteandepi-zoophyteload(pope1939,Cagle1950,boyer1965,shelbyandJensen2002),andasaresponsetoillnessorinjury(selmanandQualls2009).thecaseofaquaticbaskingwouldseemclearlyrelatedtothermoregula-tionsinceitwasexposedtofullmiddaysunlightandistheearliestspringdaterecordedforbaskingwhenwatertemperatureswererelativelylow.ourothertwoobservationsbothinvolvedturtlesintheshade,ewert’s(1976)observationwasunderalightlyovercastsky,andthomas(2009)reportedtheindividualhesawwasinpartialsunlight.Althoughmostindividualsthathavebeenobservedwereexposedtosunnyskiesasonewouldexpectofaturtlebaskingforthermoregulation,indirectultravioletlightassoci-atedwithvitamin-Dsynthesiscouldstillreachaturtleunderacloudyskyorintheshade,butmuchlesseffectivelythanexposuretodirectsunlight.bothoftheaerialbaskingindividualsweobservedhadlargeleechesonthecarapace,andforoneofthetwo,wewereabletodocumentthattheleechreleaseditsinitialholdandmovedovertimeastheturtle’sshelldried.thiswassimilartoobservationsofGraptemysbyselmanetal.(2008)and
selmanandQualls(2009);however,thomas(2009)noted100+leecheswerestillattachedtothejuvenilehecapturedwhilebasking.
AcknowledgmentsthisresearchwasperformedunderlouisianastatescientificCollectingpermitlnhp–09–059andU.s.FishandWildlifeservicespecialUsepermit42651–09–03.FundingwasprovidedbythelouisianaDepartmentofWildlifeandFisheriesandtheU.s.FishandWildlifeservice,DivisionofFederalAid,throughthestateWildlifeGrantsprogram.headstartingwasundertakenbythenatchitochesnationalFishhatchery.WewouldliketothankthestaffofblackbayoulakenationalWildlifeRefuge,andKarenKilpatrickatthenatchitochesnationalFishhatcheryfortheircoopera-tion.WethankD.ligonforhelpfulcommentsonthemanuscript.
Literature CitedAuth,D.l.1975.behavioralecologyofbasking in theYellow-belliedturtle,
Chrysemys scripta scripta (schoepff).Bulletin of the Florida State Museum, Biological Sciences20:1–45.
boyer,D.R.1965.ecologyofthebaskinghabitinturtles.Ecology46:99–118.
brattstrom,b.h.andR.Collins.1972.thermoregulation.International Turtle and Tortoise Society Journal6(5):15–19.
Cagle,F.R.1950.thelifehistoryofthesliderturtle,Pseudemys scripta troostii(holbrook).Ecological Monographs20:31–54.
ernst,C.h.andR.W.barbour.1972.Turtles of the United States.UniversitypressofKentucky,lexington.
ewert,m.A.1976.nests,nestingandaerialbaskingofMacroclemysundernatu-ralconditions,andcomparisonswithChelydra(testudines:Chelydridae).Herpetologica32:150–156.
Farr,W.,p.Crump,andJ.Caraviotis.2005.Macrochelys temminckii(Alligatorsnappingturtle).Aerialbasking.Herpetological Review36:168.
howey,C.A.F.ands.A.Dinkelacker.2009.habitatselectionoftheAlligatorsnappingturtle(Macrochelys temminckii)inArkansas.Journal of Herpetology43:589–596.
moll,e.o.andJ.m.legler.1971.thelifehistoryofaneotropicalsliderturtle,Pseudemys scripta(schoepff),inpanama.Bulletin of the Los Angeles County Museum of Natural History, Science (11):1–102.
obbard,m.e.andR.J.brooks.1979.FactorsaffectingbaskinginanorthernpopulationoftheCommonsnappingturtle,Chelydra serpentina.Canadian Journal of Zoology57:435–440.
pope,C.h.1939.Turtles of the United States and Canada.AlfredA.Knopf,newYork.
pritchard,p.C.h.1967.Living Turtles of the World.t.F.h.publications,JerseyCity,newJersey.
pritchard,p.C.h.1989.The Alligator Snapping Turtle: Biology and Conservation.milwaukeepublicmuseum,milwaukee,Wisconsin.
pritchard,p.C.h.andW.F.Greenhood.1968.thesunandtheturtle.International Turtle and Tortoise Society Journal2:20–25.
selman,W.,b.Drescher,andC.Qualls.2009.Macrochelys temminckii(Alligatorsnappingturtle).Adultbaskingbehavior.Herpetological Review40:79.
selman,W.andC.Qualls.2009.Graptemys flavimaculata(Yellow-blotchedmapturtle).baskingandparasiteremoval.Herpetological Review40:78–79.
selman,W.,D.strong,andC.Qualls.2008.Graptemys gibbonsi(pascagoulamapturtle).baskingandparasiteremoval.Herpetological Review39:216.
selman,W.andm.Willig.2010.Macrochelys temminckii (Alligatorsnappingturtle).Aerialbaskingandclimbingability.Herpetological Review41:486.
shelby,J.A.andJ.b.Jensen.2002.Macrochelys temminckii(Alligatorsnappingturtle).Aerialbasking.Herpetological Review33:304.
thomas,t.m.2009.Macrochelys temminckii(Alligatorsnappingturtle).Aerialbasking.Herpetological Review40:336.
Wang,K.1952.Geologyofouachitaparish.Geological Bulletin(28):126.
Zappalorti,R.t.1976.The Amateur Zoologist’s Guide to Turtles and Crocodilians.stackpolebooks,harrisburg,pennsylvania.
AllIGAtoRsnAppInGtURtles
