IRCFReptIles&AmphIbIAns•Vol17,no2•JUn2010 79nestInGsoFtshelltURtles

mostnestingfreshwaterturtlesminimizetheirtimespentterrestrially,leavingthewatertonestandreturningimmediatelyfollowingnest-

ing(burkeetal.1994).exceptionstothisincludesometurtlesthatmigratelongdistancestonest(e.g.,Emydoidea blandingi;Roweandmoll1991)andspeciesthatburythemselvesafternesting(e.g.,Kinosternon flavescensandK. subrubrum;Iverson1990,burkeetal.1994).putativereasonsforburrowinginKinosternonincludenestattendance/defenseandawaitingconditionsthatwouldreducestressorincreasesurvivalduringtheturtles’returntowater(Iverson1990,burkeetal.1994).

northAmericansoftshells(Apalonespp.;Fig.1)arewellknownfortheircharacteristicbehaviorofburrowingintosandandothersoftsub-stratesunderwater(Webb1962,GrahamandGraham1991);however,littleisknownregardingtheirpropensitytoburrowterrestriallyafternest-ing.Wehaveobservedshallowterrestrial“troughs”inassociationwithnest-ingcrawlsofA. muticaandA. spinifera onsandbarsthatresultfromfemalescrawlingjustunderneaththesurfaceofthesandandresurfacingsomedis-

Terrestrial burrowing in nesting softshell Turtles (Apalone mutica and A. spinifera)

michaelV.plummer1andJ.seanDoody2

1Departmentofbiology,hardingUniversity,searcy,Arkansas72143,UsA(plummer@harding.edu)2schoolofbotanyandZoology,AustraliannationalUniversity,AustralianCapitalterritory,0200,Australia(sean.doody@anu.edu.au)

photographsbytheseniorauthor.

Afternesting,femalesoftshellshavebeenobservedtoburrowforvariabledistancesunderthesandsurfaceincloseproximitytothejust-completednest.WedescribeterrestrialburrowingbehaviorinApalone muticaandA. spiniferafromKansas,Arkansas,andlouisianaanddiscusspossiblereasonsforthebehavior.

Fig. 1.maleApalone spinifera(top)andmaleA. mutica(bottom).

Fig. 2.softshellhabitatonsandbarsoftheKawRiverinKansas(top)andnestinghabitatalongtheWhiteRiverinArkansas(bottom).

80 IRCFReptIles&AmphIbIAns•Vol17,no2•JUn2010

tanceaway.WealsohaveobservedtheprocessoftroughexcavationinoneA. mutica. Collectively,wehaveobservedatotalof8troughsofA. muticaonsandbarsoftheKansasRiverinKansas(plummer1976,unpubl.data,7troughsofA. muticaontheWhiteRiverinArkansas(plummer,unpubl.data),and7troughsofA. spiniferaand4unidentifiedApalonetroughsontheComiteRiverinlouisiana(Doody1995).troughsvariedinlengthfrom0.5–4.0m(mean2.2±1.24msDinlouisiana)andabout20–30cminwidth.troughs(Fig.3)variedinshapefromstraighttocurvedtosinuoustofigure-eightshaped.onetroughthatappearedtobemadebyonefemaleA. muticaconsistedofthreeseparatesegmentsincloseproxim-ity,eachapproximately2–3minlength. mostnestingcrawlsofA. muticaandA. spiniferadidnotexhibittroughs(72of77;93.5%nestsofA. muticaand198of209;94.7%nestsofA. spinifera).however,5of8(63%)troughscontainednestsinKansasand11of15(73%)troughscontainednestsinlouisiana.troughswerefoundonlyduringthenestingseason(latemay–midJulyforbothspecies).exceptforbasking,thisperiodisgenerallytheonlytimethehighlyaquaticsoftshellsarefoundinterrestrialsituations(Webb1962).Wehavefoundbothpre-andpost-nestingadultfemales(Fig.4)burrowedtypicallyattheexitendofthetrough,butwehavenotfoundhatchlings,juveniles,adultmales,orsubadultfemalesintroughs.nestsmayoccuranywhereinthetrough,butusuallyweretowardoneend,mostoftenattheentrance(Fig.3b). Fewliteraturereferencesaddressnestingtroughsortheirfunction.harper(1926)notedthatnestingsoftshells(probablyA. ferox)sometimes

burrowedbeforereturningtowater.Apalonespp.generallynestonopensandbarsonsunnydays(Webb1962,plummer1976,Doody1995),whenextendedexposuretohightemperaturescouldpresumablybelethal.onehypothesisforthefunctionoftroughsisthatmothersburrowtotemporar-ilyescapehighsurfacetemperaturesandawaitoptimalconditionsforreturntowater.thisbehaviorissimilartothatofmudturtles(Kinosternon),whichnestlongdistancesfromtheiraquatichabitats(burkeetal.1994). Alternatively, burrowing turtlesmay exhibit cryptic behavior inresponsetodisturbanceorpredationrisk.Insupport,oneA. muticabur-rowedterrestriallyafterbeingdisturbedbymVpwhileshewasnesting.burrowingbyApalone is common inaquatic situations (GrahamandGraham1991).Forexample,whenapproachedfromsomedistance,indi-vidualturtleswillreadilyburythemselvesunderthesandinshallowwater(GrahamandGraham1991;JsD,pers.obs.;mVp,pers.obs.). Anotherpossiblefunctionisthatnestingturtlesburythemselvestomorecloselyassessthesuitabilityofsubstratecharacteristicssuchastem-perature.however,only5%of68A. spiniferanestsinonestudywereassociatedwiththebehavior(Doody1995).Finally,mothersmaysim-plyrespondtoaphysicalconstraint.extendedhotweatherconditionsorcoarse-grainedsandmayrendersurfacesandnotcohesive,causingthesandtocaveinonitselfwhenaturtleattemptstoexcavateachamber(Doodyetal.2004;Fig.5)orwhenhatchlingstrytoemergefromthenestchamber(mortimer1990;Fig.6).Asaconsequence,thecloselyrelatedpig-nosedturtle(Carettochelys insculpta)maynestatlowerelevationsonsandbarsduetothefriablesandathigherelevations(Doodyetal.2004);however,lowerelevationsincreasetheriskoffloodmortality.byburrowing,softshell

plUmmeRAnDDooDY

Fig. 3.(A)Acurvedtrough(dashedoutline)ofApalone spiniferaontheComiteRiverinlouisiana.(b)Astraighttrough(dashedoutline)ofA. muticaontheWhiteRiverinArkansas.theresearcherisprobingtofindtheexactlocationofthenest.

Fig. 4.Femalesoftshells,suchasthisApalone spiniferafromGinCreek,Arkansas,canbequitelarge.

A

B

IRCFReptIles&AmphIbIAns•Vol17,no2•JUn2010 81nestInGsoFtshelltURtles

motherscouldexcavateanestincohesivesandbyremovingtheuppermostloosesand.thisputativebehaviorisperhapsasimplerversionofbody-pittingdisplayedbyseaturtlesandtheAmazonianGiantRiverturtle,Podocnemis expansa(schaubleetal.2006,Vogt2008).body-pittingmayaidturtlesattemptingtonestonsandbarsthathavealayerofloose,drysand.Insupportofthishypothesis,Apalonenestsassociatedwithtroughsweredeeperthanthosewithouttroughs(Doody1995). Althoughwehavegeneratedhypothesesfortheunusual“troughing”behaviorexhibitedbysoftshells,currentevidencedoesnotallowustofavoranyparticularone.Focalobservationsofnestingturtleswouldbeparticu-larlyusefulbutdifficultgiventherelativelylowfrequencyofthebehavior.Accordingly,thethermoregulationhypothesiswouldbedifficulttotest.however,theothertwohypothesesmaybemoreeasilytestable.First,mockpredatorsorsomeotherdisturbancecouldbeintroducedtonestingturtlestotestthepredationriskhypothesis.second,thecohesivesandhypothesiscouldbeaddressedbyattemptingtoexcavateanartificialnestchambernexttothetrough.Failuretocreateachamberwouldlendsupporttothisidea(Doodyetal.2004).

AcknowledgmentsAfter informinghenryFitchabout theunusualbehaviorofanestingfemaleApalone muticathatmVphadobservedontheKansasRiverduringthe1973nestingseason,henrysaid,“Yououghttolookintothat.”Wellhenry,hereitis—thanksforthesuggestion.

Literature Citedburke, V.J., J.W. Gibbons, and J.l. Green. 1994. prolonged nesting forays

byCommonmudturtles (Kinosternon subrubrum).American Midland Naturalist131:190–195.

Doody,J.s.1995.Acomparativenestingstudyoftwosyntopicspeciesofsoftshellturtles(Apalone muticaandApalone spinifera)insouthcentrallouisiana.Unpublishedm.s.thesis,southeasternlouisianaUniversity,hammond.

Doody,J.s.,A.Georges,andJ.e.Young.2004.Determinantsofreproductivesuccessandoffspringsexinaturtlewithenvironmentalsexdetermination.Biological Journal of the Linnean Society80:1–16.

Graham,t.e.andA.A.Graham.1991.Trionyx spiniferus spiniferus(easternspinysoftshell).buryingbehavior.Herpetological Review22:56–57.

harper,F.1926.talesoftheokefinokee.American Speech1:407–420.

Iverson,J.b.1990.nestingandparentalcareintheturtle,Kinosternon flavescens.Canadian Journal of Zoology68:230–233.

mortimer,J.A.1990.theinfluenceofbeachsandcharacteristicsonthenest-ingbehaviorandclutchsurvivalofGreenturtles(Chelonia mydas).Copeia1990:802–817.

plummer,m.V.1976.someaspectsofnestingsuccessintheturtle,Trionyx muti-cus.Herpetologica32:353–359.

Rowe,J.W.ande.o.moll.1991.Aradiotelemetricstudyofactivityandmove-mentsoftheblanding’sturtle(Emydoidea blandingi)innortheasternIllinois.Journal of Herpetology25:178–185.

schauble,C.,R.Kennett,ands.Winderlich.2006.Flatbackturtle (Natator depressus)nestingatFieldIsland,Kakadunationalpark,northernterritory,Australia,1990–2001.Chelonian Conservation and Biology5:188–194.

Vogt,R.2008.Amazon Turtles.Graficabiblos,lima,peru.

Webb,R.G.1962.northAmericanrecentsoft-shelledturtles(Familytrionychidae).University of Kansas Publications, Museum of Natural History13:429–611.

Fig 5.AfemaleApalone muticaexcavatinganestalongtheWhiteRiver,Arkansas.

Fig. 6.hatchlingApalone mutica readytoemergefromanest(thetop5cmofsandhasbeenbrushedback)alongtheComiteRiver,louisiana.