Home range and movements of American alligators (Alligator mississippiensis) in an estuary habitat

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Title:
Home range and movements of American alligators (Alligator mississippiensis) in an estuary habitat
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Mixed Material
Language:
English
Creator:
Fujisaki, Ikuko
Hart, Kristen M.
Mazzotti, Frank J.
Cherkiss, Michael S.
Sartain, Autumn R.
Jeffery, Brain M.
Beauchamp, Jeffrey S.
Denton, Mathew
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Bio Med Central (Animal Biotelemetry)
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Background: Understanding movement patterns of free-ranging top predators throughout heterogeneous habitat is important for gaining insight into trophic interactions. We tracked the movements of five adult American alligators to delineate their estuarine habitat use and determine drivers of their activity patterns in a seasonallyfluctuating environment. We also compared VHF- and satellite-tracks of one of the alligators to examine tradeoffs in data quality and quantity. Results: All tracked alligators showed high site fidelity in the estuary, but estimated home range size and core-use areas were highly variable. Two alligators were relatively sedentary and remained in the upper stream zone. One alligator traveled to a transition zone between freshwater marsh and estuary habitat, but primarily remained in the upstream area. Two alligators traveled to the downstream zone into saline conditions and showed high salinity tolerance. Overall movement rates were highly influenced by salinity, temperature, and season. Both satellite and VHF radio telemetries resulted in similar home range, core-use area, and activity centers. Conclusions: This study reveals consistent use of estuary habitat by American alligators. The alligators showed variations in their movement pattern and seasonal habitat, with movement attributable to environmental factors. Although satellite-derived locations were more dispersed compared to locations collected using VHF radio-tags, data collected from VHF tracking omitted some habitat used for a short period of time, indicating the effectiveness of satellite telemetry to continuously track animals for ecosystem-scale studies. Keywords: Crocodilian, Everglades, Satellite telemetry, VHF radio telemetry
General Note:
Fujisaki et al. Animal Biotelemetry 2014, 2:8 http://www.animalbiotelemetry.com/content/2/1/8; Pages 1-10
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doi:10.1186/2050-3385-2-8 Cite this article as: Fujisaki et al.: Home range and movements of American alligators (Alligator mississippiensis) in an estuary habitat. Animal Biotelemetry 2014 2:8.

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University of Florida
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University of Florida
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© 2014 Fujisaki et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
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RESEARCHOpenAccessHomerangeandmovementsofAmerican alligators( Alligatormississippiensis )inanestuary habitatIkukoFujisaki1*,KristenMHart2,FrankJMazzotti1,MichaelSCherkiss2,AutumnRSartain3,BrianMJeffery1, JeffreySBeauchamp1andMathewDenton2AbstractBackground: Understandingmovementpatternsoffree-rangingtoppredatorsthroughoutheterogeneoushabitat isimportantforgaininginsightintotrophicinteractions.WetrackedthemovementsoffiveadultAmerican alligatorstodelineatetheirestuarinehabitatuseanddeterminedriversoftheiractivitypatternsinaseasonallyfluctuatingenvironment.WealsocomparedVHF-andsatellite-tracksofoneofthealligatorstoexaminetradeoffs indataqualityandquantity. Results: Alltrackedalligatorsshowedhighsitefidelityintheestuary,butestimatedhomerangesizeandcore-use areaswerehighlyvariable.Twoalligatorswererelativelysedentaryandremainedintheupperstreamzone.One alligatortraveledtoatransitionzonebetweenfreshwatermarshandestuaryhabitat,butprimarilyremainedinthe upstreamarea.Twoalligatorstraveledtothedownstreamzoneintosalineconditionsandshowedhighsalinity tolerance.Overallmovementrateswerehighlyinfluencedbysalinity,temperature,andseason.Bothsatelliteand VHFradiotelemetriesresultedinsimilarhomerange,core-usearea,andactivitycenters. Conclusions: ThisstudyrevealsconsistentuseofestuaryhabitatbyAmericanalligators.Thealligatorsshowed variationsintheirmovementpatternandseasonalhabitat,withmovementattributabletoenvironmentalfactors. Althoughsatellite-derivedlocationsweremoredispersedcomparedtolocationscollectedusingVHFradio-tags, datacollectedfromVHFtrackingomittedsomehabitatusedforashortperiodoftime,indicatingtheeffectiveness ofsatellitetelemetrytocontinuouslytrackanimalsforecosystem-scalestudies. Keywords: Crocodilian,Everglades,Satellitetelemetry,VHFradiotelemetryBackgroundAnimalmovementsareoftendeterminedbyresource needandevolutionaryhistory,andsuchmovementscan, inturn,affecttheenvironmentaswellasotherorganisms [1].Dataonmovementpatternsiscriticalforunderstandingecologicalprocessesandinformingconservation,particularlyforfocalspeciesthatplaycrucialrolesinshaping ecosystemfunction[2-4].Findinglinkagesbetweenindividualmovementsandthespatiallyandtemporallyheterogeneousenvironmentcanhelpdeterminedriversof animalmovement[5].However,conductingwell-designed experimentstotesthypothesesaboutthedriversofanimal movementsischallenging,especiallyforlargemobileanimalsinremoteareas. Arangeoftelemetrytechniquesmakeitpossibleto remotelyobservefree-ranginganimalsofvarioustaxa, allowingresearcherstoaddressfundamentalquestionsrelatedtospatialecologyandanimalbehavior[3].Theselectionofaparticulartechniquedependsonstudyspecies andresearchquestions.Movementsofcrocodilianspecies, large-sizedmobileaquaticpredatorsfrequentlyinhabiting remoteareas,havebeeninvestigatedwithVHFradiotelemetryandin-wateracousticreceivers[6,7].Thesetelemetrytechniqueshaverevealedtheabilityoftruenavigation andadaptationofindividualmovementtactics[6,7]of Americanalligators( Alligatormississippiensis ).Inanother *Correspondence: ikuko@ufl.edu1Ft.LauderdaleResearchandEducationCenter,UniversityofFlorida,Davie, FL,USA Fulllistofauthorinformationisavailableattheendofthearticle 2014Fujisakietal.;licenseeBioMedCentralLtd.ThisisanOpenAccessarticledistributedunderthetermsoftheCreative CommonsAttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,distribution,and reproductioninanymedium,providedtheoriginalworkisproperlycredited.TheCreativeCommonsPublicDomain Dedicationwaiver(http://creativecommons.org/publicdomain/zero/1.0/)appliestothedatamadeavailableinthisarticle, unlessotherwisestated.Fujisaki etal.AnimalBiotelemetry 2014, 2 :8 http://www.animalbiotelemetry.com/content/2/1/8

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studyofAmericanalligatorhomerangesinmarshhabitat, researchersusedradiotransmitterstoconductintensive dailyandweeklytracking[8].However,suchtrackingislogisticallychallengingformonitoringmovementsofhighly mobilespeciesformoreextendedperiodsinremoteareas. Satellitetelemetryhasbeenrecommendedasabetter tooltogatherlocationdataoncrocodiliansoverextended spatialandtemporalscales[9].RecentlyGPS-another contenderinremotetelemetrytechniques-wasusedwith acoustictelemetrytotracktwoalligatorsintheEverglades estuary[10]andwiththesetools,researchersdeciphered differentmovementpatternsbetweenthetrackedanimals. WhereasGPStelemetryisaviablealternativeforremotely monitoringanimalmovements,thelowercostandincreasedbatterylongevityisanadvantageofsatellitetelemetry.Theeffectivenessofsatellitetelemetrytotrack crocodilianmovementswasshownfor Crocodylusporosus inanestuaryhabitatinCapeYorkPeninsula,Australia [11].However,thetrackedcrocodilesexhibitedlargescale movementsaroundthecoastline.Therefore,theeffectivenessofsatellitetelemetrytotrackspeciesmovementsover asmallerecosystem-scaleremaineduncertain. TheAmericanalligatorisahighlymobileapexpredator thatresidesinsomeremoteandhard-to-accessestuarine habitats.AlthoughtheyprimarilyinhabitfreshorlowsalinitywaterthroughoutthesoutheasternUSA,theyare alsoknowntoforageinhighersalinitywateraslongasthey haveperiodicaccesstofreshwater[12-14].Alligatorsconsumevariousorganismssuchasfish,birds,andother aquaticfauna[15],andtheyplayaroleastop-predator, keystonespecies,andecosyst emengineer.Duetotheirecologicalimportance,alligatorshavebeenusedasanindicatorofecosystemrestorationinsouthFlorida[16].Because alligatorshavedominanttop-downeffects,understanding theirmovementbehaviorisesp eciallyimportantforinterpretingthetrophicinteractionsinasystem[10]. HistoricallyintheEverglades,Florida,Americanalligatorsweremostabundantinfreshwatersloughsandoligohaline(brackishwater)mangroveareas[17].However, duetothelossofwetlandsandalteredhydrologyinthe area,thespatialpatternoftheirhabitatusehaschanged [14].Alligatorsnowprimarilyinhabitcentralsloughs andcanals[18]fromupstreammarshestothemouthof SharkRiverestuary[7,14,18].Withinthishabitatmatrix, alligatorsdevelopindividualmovementtacticsthatresultinnutrientexchangesbetweenmarine,estuarine, andfreshwaterzones[7,10]. Distinctdryandwetseasonscauseseasonaldry-downs ofinteriormarshhabitatinsouthFlorida.Asanaquatic reptile,alligatorsneedtoobtainaccesstofreshwater sourcesandthisseasonalfluctuationofsurroundingresourceslikelyaffectstheirmovements.Therefore,weused satellitetelemetrytostudyindividualhomerangesand evaluatetherelativeimportanceofspatialandtemporal factorsinalligatormovementpatterns.Tofurtherexaminetheutilityofsatellitetelemetry,wealsocompared resultsforonealligatorusingsatellite-andVHFradiotelemetrydatasets.ResultsAlligatorlocationsandsalinitydataWeplacedsatellitetagsononefemale(F1)andfour male(M1toM4)adultalligators,rangingfrom221to 250cmtotallength,caughtintheSharkRiverestuary (Figure1andTable1).Wetrackedthealligatorsfrom March2009toApril2012;themeantrackingduration was278.6days(SD:108.7days),andrangedfrom163to 399days.Themeannumberofhigh-qualityclass3satellitelocations(LC3)usedforanalysiswas149.6(SD: 151.8,range:19-341;Table2). Wecapturedthefemale(F1)andtwoofthreemales (M1andM2)inthelesssalineupstreamzone,andthey remainedtherethroughouttheirtrackingdurations (Figure1).Wecapturedthetwoothermales(M3and M4)inthemid-estuaryanddownstreamzones,respectively,andtheyrangedacrosswiderareascomprising highsalinityzonesneartheGulf.Allalligatorsremained intheestuarythroughouttheirtrackingperiodsexcept forM1whosehomerangeincludedbothestuaryand marshhabitatinatransitionzoneabout9kmupstream fromtheoriginalcapturelocation;thismarshwasgenerallydominatedbysawgrass( Cladiumjamaicense ). Salinitywashighlyvariedspatiallyandtemporallyinthe studyarea.Accordingtothefourwatergages,thesalinity gradientfollowedthefreshwaterflowfromtheupperShark Riverdownstreamfromlowtohigh,rangingfromlessthan 1pptto38ppt(Figure2).Duringthestudyperiod,inthe upstreamwatergage(CN),dailysalinityvaluesranged from0.15to25.04ppt(mean2.734.71ppt)whereasin thedownstreamzonedailysalinityvaluesrangedfrom 16.08to38.38ppt(mean28.324.47ppt).Forallwater gages,thehighestsalinitywasrecordedduringspringto earlysummerbetweenMay30andJune6.Homerange,movement,andenvironmentalvariablesAllalligatorsdisplayedsite-fidelitytotheirhomeranges.A randomwalksite-fidelitytestshowedthattheobserved movementsofallfivealligatorsweremoreconstrained thanrandommovementpathswithinEvergladesNational Park(ENP).Theproportionoftherandommovement pathswithhighermeansquaredistancevaluesthanthe observedpathwasgreaterthan0.988forallalligators. Twoalligators,M3andM4,hadacomparablylarge numberofdailylocationsovermultipleseasons:seasons1,2,3,and4forM3andseasons1,2,and4for M4.AKruskal-Wallistestindicatedasignificantdifference( P <0.001)inlatitudeandlongitudebyseasonfor bothalligators.TheBoferronimultiplecomparisonstestFujisaki etal.AnimalBiotelemetry 2014, 2 :8 Page2of10 http://www.animalbiotelemetry.com/content/2/1/8

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showedthatbothlatitudeandlongitudeweresignificantlydifferent( P <0.05)forallpair-wisecomparisons exceptseasons3and4forM3andseasons1and2for M4.Theseseasonswerecombinedincalculatingkernel densityestimates(KDE).Homerangeandcore-usearea contoursfromtheKDEsweresuccessfullycreatedfor allalligators(Figure3).Thebandwidththatminimized leastsquarecrossvalidation(LSCV)rangedfrom123.0 to489.3m(mean261.0120.4SD)(Table2).Thesize ofthecore-useareas(thatis,50%KDE)forthefivealligatorsrangedfrom0.5to8.8km 2 (mean2.93.0SD) andthehomeranges(thatis,95%KDE)were2.7to 33.1km 2 (mean:13.111.9SD;Table2).Durationsof trackingperioddidnotcorrelatesignificantlywithcoreuseareas( r =-0.55, P =0.153)andhomeranges( r =-0.61, P =0.107).Allhomerangeswereconcentratedinriverine habitat(Figure3). Onaverage,alligatorsmovedfrom0.7to3.2kmperday (mean1.51.2SD)andthedailymovementwassignificantlydifferentbetweenanimals( K =12.8, P =0.012).The nullmodelofdailymovementresultedinconsiderably highercorrectedAkaikeInformationCriterion(AICc)comparedtoallotherparameterizedmodels(Table3).Thetop modelwiththesmallestAICcwasoneofthemostparameterizedmodelsthatinclude dsalinity,season,maximum temperature( T max ),andaninteractiontermof T max and season.TheAICcweightofthismodel(>0.99)impliesthat thereisagreatprobabilitythatthisisthetruemodel Figure1 MapofSharkRiverestuaryinEvergladesNationalPark,Floridashowingcaptureandreleaselocationsofsatellite-tagged Americanalligators( Alligatormississippiensis )andlocationsofgagingstations(SharkRiver(SR),GunboatIsland(GI),TarponBayEast (TE),andCanePatch(CN)). TheinsetboxindicatesthestudyarealocationwithinFlorida. Table1Summaryofsatellite-trackedAmericanalligators( Alligatormississippiensis ),includingtrackingperiod,sex, totallength(TL),snoutventlength(SVL),andweight,inSharkRiverestuaryinEvergladesNationalPark,Florida IDDatedeployedLastdateofobservationSexTL(cm)SVL(cm)Weight(kg) F127October20112August2012Female221.1111.627 M127March200929August2009Male243.6126.845 M229October201117November2012Male244.0125.246 M33November201111November2012Male245.4126.345 M43November201127April2012Male250.0131.148 Fujisaki etal.AnimalBiotelemetry 2014, 2 :8 Page3of10 http://www.animalbiotelemetry.com/content/2/1/8

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amongallcompetingmodels.TypeIIItestoffixedeffectsindicatedthatsalinity( F 1,210 =5.42, P =0.021),season ( F 3,210 =2.72, P =0.046),andtheinteractionofseasonand T max ( F 3,210 =2.85, P =0.038)significantlyaffecteddaily movementforthealligators.Dailymovementwashigher whendailysalinitywashigher( B salinity =51.822.2SE). ComparingsatelliteandVHFradiotelemetries BoththeVHFandsatellitetagsonalligatorM1transmitted longenoughforacomparisonofeffectiveness.Thesatellite tagstoppedtransmittingon28August,154daysafterthe release.TheVHFcontinuedtotransmitasignalasof9 October2009(196daysafterrelease).Intotal,22biweekly flightswereperformedtotrackthealligatorwiththeVHF signal,resultingin22locations.Duringthesameperiod, 226satellitelocationswererecordedfrom92uniquedays. UsingonlydatawithLC3,39satellite-trackedlocations from35uniquedayswereavailableforanalysis. Allsatellite-andVHF-track edlocationswerealongthe upperestuaryzone,however,itappearedthatVHFsurveys missedthehabitatusedinafurtherupstreamareawhere M1traveledduringa2-weekVHFsurveyinterval(Figure4). High-qualitysatellite-trackedlocationstendedtobe spatiallymoresparsethanVHF-derivedlocations;standarddeviationsinbotheastingandnorthingUTMsof satellite-derivedlocationsweremuchlarger(818.0mfor eastingand513.8mfornorthing)thanthosederivedfrom VHFsurveys(136.9mforeastingand225.4mfornorthing).Thisis,inpart,becausesatellitetelemetrydetected thesecondaryhabitatthatM1usedforashort-period. Usinga200mbandwidth,approximatelythebandwidth thatminimizedLSCVwithsatellitedata(Table2),satellitetrackedlocationsresultedinlargerKDEs(2.58km 2 for Table2Summaryofsatellitedataandmovementparameters,kernelsize(h lscv ;estimatedusingfixedkernelleast squarecrossvalidation(LSCV)),andareasof50%and95%kernelcontours,derivedusingLC3data IDSeasonDetections(n)Dayswithdetection(n)h lscv (m)Areaof50%KDE(km 2 )Areaof95%KDE(km 2 ) F1All1918163.70.542.95 M1All5242201.50.552.85 M2All4940317.61.355.58 M316639168.60.472.69 27650327.93.8321.23 3&4199119293.35.3925.36 M41&219896123.01.8710.94 48941489.38.8433.11 Kerneldensityestimates(KDE)werecalculatedwithalllocationdataforF1,M1,andM2,andbyseasonforM3andM4,whereseason1isfromJanuarytoMar ch, season2isfromApriltoJune,season3isfromJulytoSeptember,andseason4isfromOctobertoDecember. Figure2 DailysalinityatfourmonitoringgagesplacedinSharkRiverestuary(SharkRiver(SR),GunboatIsland(GI),TarponBayEast (TE),andCanePatch(CN,seeFigure1))anddailymaximumairtemperatureinEvergladesNationalParkin2011. Fujisaki etal.AnimalBiotelemetry 2014, 2 :8 Page4of10 http://www.animalbiotelemetry.com/content/2/1/8

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95%KDEand0.52km 2 for50%KDEs)thanthosecalculatedwithVHF-trackinglocations(1.36km 2 and0.24km 2 ). BoththeVHF-derivedandsatellite-derivedcore-useareas wereinsimilarlocationsandthesatellite-derivedcore-use areascontainedthevastmajority(97%)oftheVHF-derived core-usearea.Centroidsofthe50%KDEsfrombothtrackingmethodswereabout150mapart(Figure4). Discussion Ourstudydepictsvariationinthehomerangeandmovementpatternsofsatellite-trackedalligators.Althoughthe resultsmaybepartiallyattributedtodifferencesintracking durationandthenumberofsatellite-derivedlocations [19,20],thepresenceofvariationbetweenindividuals andbyseasonareclear.Inapreviousstudyinthesame location,researchersusedsta tionaryin-wateracoustic receiversandtheorizedthatalargeportionoftaggedalligatorslikelyleftthemonitoredareaformarshhabitat [7].Allofouralligatorsexhibitedquantifiablyhighsite Figure3 Satellitelocations(darkpoints),estimatedcore-useareas(50%kerneldensitycontour;darkertone),andhomeranges (95%kerneldensitycontour;lightertone)ofonefemale(F1)andfourmale(M1,M2,M3,andM4)Americanalligators( Alligator mississippiensis )trackedusingsatellitetelemetryintheSharkRiverestuary,EvergladesNationalPark. Kerneldensityestimates(KDE) werecalculatedwithalllocationdataforF1,M1,andM2,andbyseasonforM3andM4,whereseason1isfromJanuarytoMarch,season2is fromApriltoJune,season3isfromJulytoSeptember,andseason4isfromOctobertoDecember. Table3Resultsofthemodelcomparisonusingcorrected AkaikeInformationCriterion(AICc) ModelAICc AICcAICcweight Salinity,season,T max season,T max 4,020.40>0.999 Salinity,season,salinityseason,T max 4,031.711.3<0.001 Salinity,season,T max 4,064.143.7<0.001 Season,T max 4,094.574.1<0.001 Salinity,T max 4,131.7111.3<0.001 T max 4,161.1140.7<0.001 Salinity,season,salinityseason4,386.2365.8<0.001 Salinity,season4,418.1397.7<0.001 Season4,453.9433.5<0.001 Salinity4,499.6479.2<0.001 Null4,531.6511.2<0.001 Nullmodelistheinterceptmodel.Allmodelsincludedrandomeffectof alligators.Thesymbol denotesinteractioneffect. Fujisaki etal.AnimalBiotelemetry 2014, 2 :8 Page5of10 http://www.animalbiotelemetry.com/content/2/1/8

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fidelitytotheriverineareas,indicatingthatourtaggedalligatorswereresidentintheestuaryduringthemonitored periods.However,onealligator(M1)traveledfurthernorth toatransitionzonebetweenriverandfreshwatermarsh forashortperiod,whichisnotinconsistentwiththepreviousstudy[7].Withintheestuary,alligatorsshowedhighly variablehabitatusepatterns.Satellite-trackedalligatorseitherremainedinthemid-toupper-estuarybrackishwater (F1,M1,andM2)ortraveledintermittentlytothedownstreamzoneadjacenttotheGulf(M3andM4).Whereas ouralligatorsmaynothaveleftthemonitoredareaaspresumedinthepreviousstudy,themovementswediscoveredareconsistentwiththefindingsofthatstudy,asthey demonstratedthatalligatorsadapttheirmovementtactics inaheterogeneousestuarinehabitat[7]. Overall,thedailymovementsweestimatedweremuch higherthanpreviousratesfrommarshandcanalhabitats insouthFlorida[8]butwerecomparablewiththerangeof individualsestimatedbyacoustictelemetryinthesame studyarea[10].Previousstudieshaveshownthatalligator movementsvarybyecologicalsystemandindividualtraits. Severalofthesestudiesshowedalligatorshavearelatively sedentarynature[8,21],whereasothersshowedtheircapabilityoflong-distancetravel[22,23].Ourresults,combinedwiththoseinpreviousstudies,suggeststhatalligator movementandhomerangebehaviorareinfluencedby habitataswellasindividualspecializationinforagingtacticsandpreypreference[7,10]. Whereasthisstudyisbasedonasmallnumberof taggedalligators,theresultsindicatethattheirmovement rateisattributedtoanumberofenvironmentalfactors. Salinityisonefactorintheenvironmentthatcouldinfluencealligatormovements.Adultalligatorscantolerate highsalinitywateraslongastheyhaveperiodicaccessto freshwater[24,25].Thesalinitymeasurednearthemouth oftheestuary(stationSR;Figure1),wheretwomalealligators(M3andM4)traveled,becameashighas30.7ppt (mean25.02.6SD).Previousresearchershavedescribed daily,relativelyshortdistanceexcursionsintoseawaterby alligators,presumablytofeed[24,25].Whatrecentstudies [7,26]discovered,andweconfirmed,isthatalligators makelongerdistancemovementstomarineconditionsfor longerperiodsoftime,alsopresumablytofeed.Largealligatorshavesometolerancetosalineconditionsaslongas throughdiet,rainwater,ormovementtheydonotbecome dehydrated[27];feedingonvertebratepreywouldeasethe osmoticburdenofasea-goingalligator.Inourstudy,it didappearthatadultalligatormovementwasinfluenced bythesalinityofestuarinewater,asdailymovementrates increasedwhensalinityincreased. Ourresultisconsistentwithpreviousstudiesofalligator homerangeandmovementsinwhichseasonalvariation wasfound[28];inspring,bothmalesandfemalesshowed increasedmovementratesinanorthcentralFloridalake. MalealligatorsinacoastalmarshinLouisianaareknown toextendrangesizeandmovementrateduringthespring breedingseason[22].Duringsummer,alligatorstendtoreduceactivityrange[28],likelyduetoincreasedmetabolic costsunderincreasedambienttemperature[29].Likewise, wefoundalligatormovementswereinfluencedbyseason, temperature,andtheinteractionofthesetwofactors. Satellitetelemetrywasaneffectivetoolthatenabled ustodecipherthemovementsofalligatorsatourstudy site.Ingeneralsatellitetelemetrycanbeusefulforunderstandingecosystem-scalehabitatuseandmovement patternsofwildlife.Ithasbeenprevalentinstudieson largescalemovementsoffree-ranginganimals,suchas migratorybirds[30]andlargemarinevertebratessuch aswhales[31],seals[32],andseaturtles[33,34].These speciesfrequentlytravellongdistancesacrossdifferent climaticzonesorevenmakecontinentalmovements (forexample,[35])inwhichpotentiallocationerrors arecomparablyminor.Althoughinsomecasesalligatorsexhibitedlongdistanc etravelwithdispersalinto differentsystems[36],theirmovementscaleistypically smaller.Toaccountforthesmallerscaleandminimize locationerrorsinourdataset,weusedonlythehighest qualitylocationdata(LC3). Fromthishigh-qualitysat ellitedata,wedelineated relativelysmall-sizedcore-useareasandhomerangesof Figure4 Observedlocations(blackdots)andestimatedkerneldensitycontoursofamalealligator(M1)usingsatellite(A)andVHF radiotelemetries(B). Darkerandlightertonepolygonsare50%and95%kernelcontours,respectively.Starsrepresentthecentroidofthe50% kernelcontours. Fujisaki etal.AnimalBiotelemetry 2014, 2 :8 Page6of10 http://www.animalbiotelemetry.com/content/2/1/8

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alligatorsintheEvergladesestuary.Althoughdirectcomparisonisnotrelevantduetodifferencesinbothfieldand analyticalapproaches(LC3locationsofsatellitetelemetry canbeoffby250m),itappearedthattheestimatedcoreusearea(0.54-1.35km2)ofthethreealligatorsthat remainedinsmallranges(F1,M1,andM2)wascomparabletothecore-useareasofmarsh(0.3km2)andcanal (0.43km2)alligatorspreviouslyestimatedusingradiotelemetry[8].Incontrast,theothertwomales(M3andM4) exhibitedmuchlargerseasonalcore-useareas(0.478.84km2)thantheradiotelemetry-trackedalligators. Duetologisticalreasons,comparisonbetweensatellite andVHFtelemetrieswasbasedonasingleanimalfora limitedterm.However,thiscomparisonelucidatedseveral issuesthatneedtobeconsideredwhenselectingatrackingtechnique.Thehighest-qualitysatellite-derivedlocationsweremoredispersedthanVHFlocationswhich resultedinalargerhomerangeandcore-useareaestimate forthesatellitedata.However,bothtelemetrymethods pinpointedthesamegeneralhomerange,core-usearea, andlocationandnumberofactivitycentersforalligator M1.Continuousobservationwithsatellitetelemetryalso enabledustodetecttheuseofasecondaryhabitatwhere thealligatortraveledforashorttimeduring2weekswith noVHFflight.Althoughreducedlocationaccuracyisa drawbackofsatellitetelemetry,itsclearadvantage,in additiontocosteffectivenessandlesslaborintensity,is thatitallowsfinertemporalobservationsoftrackedanimalscomparedtoVHFtelemetry.Thesefinertemporal observationsofsatellitetelemetryarealsoanadvantage overacoustictelemetryatfixedlocations.Currently,varioustelemetrymethodsareavailabletotrackfree-ranging animals,butselectionofamethodisfrequentlylimitedby logistics.Forexample,GPStelemetryoffersimprovedlocationaccuracywith24hoursofglobalcoverage[37],but itshighcostcouldleadtoanecessaryreductioninsample sizeforagivenstudy[7].ConclusionsUsingsatellitetelemetry, wedelineatedalligatorhome rangesandcore-useareasandquantifiedhighsitefidelitywithintheestuaryhabitatinourstudysite.Wealso foundinter-estuarymovementstoareasofhighsalinity bysomealligators,suggestingindividualvariationin habitatuse.EventhoughAmericanalligatorsoccupyestuarinehabitatasonlyasmallportionoftheirentire range,consistentuseofsuchhabitatbysatellite-tracked alligatorshighlightsitsimportanceforthistoppredator andecosystemengineer.Ourstudyareaisinfluenced bywatermanagementpracticesintheupstreamzone andwaterflowshavebeendramaticallymodifiedin thepastfordevelopment[38].Understandinghabitatinfluencedmovementsaswellasindividualvariationin movementsandhomerangebehaviorsofalligators providesinsightforsystem-wideplanning,management andconservation.MethodsStudyareaThestudywasconductedintheSharkRiverestuary withinENP,Florida(Figure1).SharkRiversloughisa majorflowwayinENP.Theuppersloughisafreshwater wetlandbuiltuponanaturaldepressioncontainingpeat soils.Thelowersloughisamangroveestuary.Intheestuary,mangroveforestsdominateprimaryproduction.Salinitygradientsareinfluencedbyrainfall,tide,andfreshwater flowintoSharkRiverthatisinpartdeterminedbywater managementactivities[39].DataWecapturedalligatorsintheSharkRiverestuarybetweenMarch2009andMarch2012usingwire-nooses asdescribedpreviously[40].Wemeasuredeachanimal fortotallength(TL),snout-ventlength(SVL),andweight. Wealsodeterminedsexandnotedanyabnormalitiesor deformities.Wetaggedallig atorsusinguniqueFlorida FishandWildlifeConservationCommissionwebtags, andaffixedbothaSPOT5sat ellitetag(WildlifeComputers,2AAstacked,71.534.024.4mm)anda VHFradiotag(HolohilmodelsSI-2,11g)toeachone. ForalligatorM1,weattachedtheSPOT5transmitter usingstainlesssteelwir eplacedthroughthenuchal scutesandPVCtubing.Wethenreinforceditwitha twopartepoxy.Fortheremainingfourindividuals,we attachedtheSPOT5transmitterasinapreviousstudy [41].Weprogrammedthetagstobeoncontinuously, anduponcompletionofattachmentwereleasedallindividualsattheiroriginalcapturelocation.Location datafromthesatellitetagswasreceivedonlineusing SatelliteTrackingandAnalysisTool(STAT)[42].For alligatorM1,weeklyVHFmonitoringflightswereperformedfromafixed-wingaircraft(Cesna182),flyingat speedsbetween100and140km/hataltitudesbetween 152and610m.WeusedaHabitOspreyVHFtelemetry receiverandtwoHantennas,onemountedtoeach wingoftheairplane,tomonitortelemetrysignals.Once weidentifiedwherethesignalwasstrongest,wetook additionalstepstoensureourlocationwasaccurate.To dothiswechosealandmarkwherethesignalstrength wasgreatest.Wethenapproachedthisspotfromseveral directions,isolatingthesignalwithoneantennaata time,makingitpossibletoknowwhichsideoftheplane thesignalwascomingfrom.Afterconfirmingthelocationofthestrongestsignal,wetookafinalpassoverthe landmarkandrecordedthelocationusingthehandheld GPSunit.Wedidnotvisuallyidentifytaggedanimals duetodifficultyinobservinganimalsfromtheaircraft.Fujisaki etal.AnimalBiotelemetry 2014, 2 :8 Page7of10 http://www.animalbiotelemetry.com/content/2/1/8

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Dailysalinitymeasurementswereautomaticallyrecordedatfourgagingstations(Figure1)intheSharkRiver estuaryandretrievedfromtheU.S.GeologicalSurvey SouthFloridaHydrologyDatabase(GHA,TJSandKMB, unpublishedwork).Thegageswerelocatedfrom2.5to 7.5kmapartspanningtheupperstreamtothemouth oftheriver.Weusedairtemperaturedatafromaweatherstation(EvergladesstationmaintainedbyFlorida ClimateCenter)locatedabout55kmstraight-linedistance (25.85N,-81.38W)fromthestudyarea;thisstationrecordsdailyminimumandmaximumtemperatures.Estimatinghomerangeandcore-useareaWeusedSTAT[42]tofilterlocationdatabylocation qualityandmovementspeed.WiththeArgossystem, eachsatellite-detectedlocationisassociatedwithoneof sixLCs.Estimationsofthelocationaccuracyis,3,2,1, 0,A,B,andZ,inorderfrombesttoworst.Duetothe relativelysmallmovementrangeweanticipated,weonly usedthehighestqualitylocationdata,LC3,whichhas theestimatedlocationaccuracywithin250m[43].We alsofilteredoutlocationswithmovementspeedsgreater than5kmperhour. Totestsitefidelity,weconductedMonteCarloRandomWalksimulationsusingAnimalMovementAnalysisExtensionforArcView3.2.Wegenerated1,000 randompathsandtestedwhethertheobservedmovementpathsforeachanimalweremorespatiallyconstrainedthantheserandompaths[44].Weboundedthe pathsatthe10misobathwithinEvergladesNational Park,whichcomprisesmajorfreshwaterwetlandandestuaryhabitat. Todeterminecore-useareas,wegenerateddailymean locationsforeachalligatorfromthefilteredlocations; thisminimizedpotentialautocorrelationduetomultiple observationsclosetogetherintime.Followingprevious studies[45,46],weappliedfixedkernelLSCVtoKDEs usingtheHomeRangeToolwithArcGIS9.3[47].We considered50%contourareastobecore-useareasand 95%contourareastobehomerangesforindividualalligators.Foralligatorswithalargenumberoflocationsin multipleseasons,weconductedaKruskal-Wallistest followedbyaBonferronimultiplecomparisontodetect differencesinlatitudeandlongitudebetweenseasons.If theseasonaldifferenceinthecoordinateswassignificant,wecreatedseparateKDEsforeachseason.We calculatedPearson ’ scorrelationcoefficient( r )between durationoftrackingperiodandcore-useareaandhome rangestoexamineeffectsofthedurationontheestimatedareas. Basedonnestingchronologyandphenologyofalligators[14]andtheannualrainfallpatterns,wedefined fourseasons:wintertoearlyspringdryseason(January toMarch,season1),springtoearlysummerwetseason whencourtshipandnestingoccur(ApriltoJune,season2), wetseasonincubationandhatchlingperiodinsummer (JulytoSeptember,season3),andfalltoearlywintertransitionperiodfromwettodryseason(OctobertoDecember, season4).Assessingrelationshipbetweenmovementrateand environmentalvariablesWecalculateddailymovementdistancesusingdailymean locationsfromconsecutivedays.Wedefinedsalinityfor eachdailymeanlocationfromthedailysalinityrecorded atthegagenearesttoeachlocation.Dailyminimumand maximumtemperaturesrecordedattheweatherstation werehighlycorrelated( r =0.99),andalligatormovements maybeconstrainedbythehighmetaboliccostunderhigh ambienttemperature[29]sowechosetousedailymaximumtemperature( Tmax).Weusedtheresultingdaily movementdistanceandsalinitydatatotesttheeffectof salinity,season,andtemperatureonthemovementrates ofthefivealligators,aswellasfortheKruskal-Wallisto testthedifferencesinthedailymovementratesbetween individuals. Wetested11modelsbuiltuponbiologicalhypotheses. Thenullmodel(interceptmodel)assumedthatthedifferenceindailymovementismerelyafunctionofindividualdifference(thatis,arandomeffect).Thesingle factormodelassumedthatthemovementdifferencewas influencedbyoneofthreefactors:season,salinity,or Tmax.Thetwofactormodelassumedthatcombinations ofsalinityandseason, Tmaxandseason,andsalinityand Tmaxindependentlyinfluencedmovement,butdidnot interact.Thethreefactormodelassumedthatthemovementratewasinfluencedbysinglefactorsofsalinity, season,and Tmax,orsalinity,seasonandaninteraction ofsalinityandseason.Finally,wetestedtwofour-factor modelswhichincludedsalinity,season, Tmaxandsalinity andseasoninteractionor Tmaxandseasoninteraction. Differencesbetweenalligatorswereaccountedforasa randomeffectandwereincludedinallmodels.Wefitted themodelusingSASMIXEDprocedureandcalculated AICc, AICc,andAICcweightformodelcomparison. Following[48]weconsideredthat AICc<2indicated substantialmodelsupport,valuesof4-7indicatedconsiderablylesssupport,andvalues>10hadnosupport.ComparingsatelliteandVHFtelemetriesWecomparedsatellite-andVHFradio-derivedhome rangesandcore-useareas,asdefinedby95%and50% KDEcontours,usinglocationdataforthemalealligator (M1)onwhichbothtagsweredeployed.Sincekernel densityestimatorsdependonthechoiceofbandwidth, weusedthesamebandwidthforbothsatelliteandVHF data.Thisallowedustoassessanydifferencethetelemetrymethodhadonthehomerangeandcore-useareaFujisaki etal.AnimalBiotelemetry 2014, 2 :8 Page8of10 http://www.animalbiotelemetry.com/content/2/1/8

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estimates.Forthiscomparison,weusedsatellitedata onlyduringtheperiodwhenVHFsurveyswereconducted.WeusedonlysatellitedatawithLC3(thebest locationclass)andderivedthedailymeanlocationto minimizelocationerrorandspatialcorrelation.Competinginterests Theauthorsdeclarethattheyhavenocompetinginterests. Authors ’ contributions IFperformeddataanalysisandwrotethedraftofthepaper.KMHinitiated thestudyandcontributedtothewriting.MSCoversawfieldworkand contributedtothewriting.FJMcontributedtothewriting.ARSprepared dataforanalysisandcontributedtothewriting.BJ,JB,andMDconducted fieldwork.Allauthorsreadandapprovedthefinalmanuscript. Acknowledgements FundingwasprovidedbytheGreaterEvergladesPriorityEcosystemsScience programoftheU.S.GeologicalSurvey,theU.S.ArmyCorpsofEngineersand Lacoste/SaveYourLogoFDB.Researchandcollectingpermitswereissued bytheFloridaFishandWildlifeConservationCommission(SPGS-13-58)and EvergladesNationalPark(EVER-2012-SCI-0010),andresearchmethodswere approvedbytheInstitutionalAnimalCareandUseCommitteeofthe UniversityofFlorida(IFASARC005-12FTL)andareavailableforreview.We alsothankRafaelCrespo,EdwardLarrivee,andThomasSelbyforassistance withalligatorcaptureandtransmitterattachment.Anyuseoftrade,product orfirmnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheU.S.Government. Authordetails1Ft.LauderdaleResearchandEducationCenter,UniversityofFlorida,Davie, FL,USA.2U.S.GeologicalSurvey,SoutheastEcologicalScienceCenter,Davie, FL,USA.3CNTS,contractedtoU.S.GeologicalSurvey,SoutheastEcological ScienceCenter,Davie,FL,USA. 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