Terrestrial burrowing in nesting softshell Turtles (Apalone mutica
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IRCF REPTILES & AMPHIBIANS • VOL 17, NO 2 • JUN 2010 79 NESTING SOFTSHELL TURTLES M ost nesting freshwater turtles minimize their time spent terrestrially, leaving the water to nest and returning immediately following nest- ing (Burke et al. 1994). Exceptions to this include some turtles that migrate long distances to nest (e.g., Emydoidea blandingi; Rowe and Moll 1991) and species that bury themselves after nesting (e.g., Kinosternon flavescens and K. subrubrum; Iverson 1990, Burke et al. 1994). Putative reasons for burrowing in Kinosternon include nest attendance/defense and awaiting conditions that would reduce stress or increase survival during the turtles’ return to water (Iverson 1990, Burke et al. 1994). North American Softshells (Apalone spp.; Fig. 1) are well known for their characteristic behavior of burrowing into sand and other soft sub- strates under water (Webb 1962, Graham and Graham 1991); however, little is known regarding their propensity to burrow terrestrially after nest- ing. We have observed shallow terrestrial “troughs” in association with nest- ing crawls of A. mutica and A. spinifera on sandbars that result from females crawling just underneath the surface of the sand and resurfacing some dis- Terrestrial Burrowing in Nesting Softshell Turtles ( Apalone mutica and A. spinifera) Michael V. Plummer 1 and J. Sean Doody 2 1 Department of Biology, Harding University, Searcy, Arkansas 72143, USA ([email protected]) 2 School of Botany and Zoology, Australian National University, Australian Capital Territory, 0200, Australia ([email protected]) Photographs by the senior author. After nesting, female Softshells have been observed to burrow for variable distances under the sand surface in close proximity to the just-completed nest. We describe terrestrial burrowing behavior in Apalone mutica and A. spinifera from Kansas, Arkansas, and Louisiana and discuss possible reasons for the behavior. Fig. 1. Male Apalone spinifera (top) and male A. mutica (bottom). Fig. 2. Softshell habitat on sandbars of the Kaw River in Kansas (top) and nesting habitat along the White River in Arkansas (bottom).
Transcript of Terrestrial burrowing in nesting softshell Turtles (Apalone mutica
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([email protected])2schoolofbotanyandZoology,AustraliannationalUniversity,AustralianCapitalterritory,0200,Australia([email protected])
photographsbytheseniorauthor.
Afternesting,femalesoftshellshavebeenobservedtoburrowforvariabledistancesunderthesandsurfaceincloseproximitytothejust-completednest.WedescribeterrestrialburrowingbehaviorinApalone muticaandA. spiniferafromKansas,Arkansas,andlouisianaanddiscusspossiblereasonsforthebehavior.
Fig. 1.maleApalone spinifera(top)andmaleA. mutica(bottom).
Fig. 2.softshellhabitatonsandbarsoftheKawRiverinKansas(top)andnestinghabitatalongtheWhiteRiverinArkansas(bottom).
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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
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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.
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Fig 5.AfemaleApalone muticaexcavatinganestalongtheWhiteRiver,Arkansas.
Fig. 6.hatchlingApalone mutica readytoemergefromanest(thetop5cmofsandhasbeenbrushedback)alongtheComiteRiver,louisiana.
