Analysisofpossible
changein ecological characterofthe RoebuckBayand EightyMileBeach Ramsarsites
DraftReport
PreparedfortheDepartmentof Sustainability, Environment,Water,Populationand theCommunities
byBennelongiaPtyLtd
May2010
Analysisof possiblechangeinecological
characteroftheRoebuckBayandEighty
MileBeachRamsarsites
BennelongiaPtyLtd
5BishopStreetJolimont WA6913 ACN124110167
Report84/2010
May2010
Coverpicture.RedKnot
From
Arthur Morris,Birds as Art
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Draftreport / Vers.1 / JamesRichardson / GaylePartridge / email / 13.v.10StuartHalse
Finalreport / StuartHalseJames / email / 23.vi.10
Richardson
EXECUTIVESUMMARY
North-westWesternAustralia supportsmorenon-breedingmigratoryshorebirdsthananyotherareaof
AustraliaanditisoneofthemoreimportantareasforshorebirdsintheEastAsia-Australasian Flyway. EightyMileBeachandRoebuckBaycontainthemajorconcentrationsofmigratoryshorebirdsinnorth- westWesternAustralia andwerebothnominated asRamsarsitesin1990. Ithasrecentlybeen suggested that shorebirds have declined at Eighty-mile Beach over the last decade. This report examines whethertheremayhavebeendeclinesinnumbers ofmigratory shorebird speciesatthetwo Ramsarsitesinnorth-westWesternAustralia,Eighty-mileBeachandRoebuckBay.
Thereporthadthreeobjectives:
• To investigate whether statistically significant changes have occurred in the numbers of migratory shorebirds counted atEighty-mile BeachandRoebuckBay,andinparticular whether numbersofGreatKnotandRedKnothavechanged.
•TodeterminewhethertheecologicalcharactersofRoebuckBayandEightyMileBeachhave changedsincelistingasaresultofanydeclineinmigratoryshorebirdnumbers.
• To determine possible causes of any declines observed in migratory shorebird numbers, includingwhetheranydeclinesmaybetheresultofhabitatchangeatstagingareasinthe YellowSea.
Theavailabledatastrongly suggesttherehasbeennodeclineinuseofRoebuck Baybymigratory shorebirds, overthepastdecadeandalsooverthepast25years,althoughthisisbasedprincipallyon datafrom thenorthernpart oftheBay. Total numbersofshorebirdsatRoebuckBayfrom 2004to2009 remainedabovethethresholdfortheshorebirdLimitsofAcceptableChangeatthatsite.
Incontrast,therehasbeenastatistically significant declineinnumbersofmigratoryshorebirds ina regularlymonitoredsector(5–40km)atthenorthernendofEighty-mileBeach. Thisdeclineisnot reflectedinlong-termanalysisofnumbersinthe5–15kmsectoroftheBeachsince1993anditis unclearwhetherthedeclineisrepresentativeoftheBeachasawhole. Speciesthresholds,aswellas totalshorebirdthresholds,ofLimitsofAcceptableChangehavebeendefinedforEighty-mileBeach basedoncountsinthenorthernpartof theBeach(0– 60km)madeduringthelastdecadeandnumbers ofBar-tailed Godwit,GreaterSandPloverandTerekSandpiper werebelowthreshold valuesforthese speciesin2009. ThesebreachesoftheLimitsofAcceptableChangeatEighty-mileBeacharelikelyto continue.
It is concludedthat a changein the ecologicalcharacterof Eighty-mileBeach,as definedby the ecologicalcharacterdescription,isoccurringasaresult ofdecliningnumbersofshorebirdsusingthe0–
60kmsectoroftheBeachduringthelastdecade. ThereappearstobenochangeatRoebuckBay.
Giventhatthere hasbeennodecline ofresidentAustralianshorebirdsandnoobvious reductioninprey availability, thedeclineofmigratoryshorebirdsinthesector0–60kmatEighty-mile Beachmaybean artefactofsurveymethodology,aconsequenceofshorebirdbiologyand preydistributions,orthe result ofreducedFlywaypopulations. ItisconsideredunlikelythatanthropogenicactivitiesonEighty-mile Beachitselfhaveaffectedmigratoryshorebirdnumbers.
The impactofspecificmudflatreclamationactivitiesinthe YellowSea (suchasatSaemangeum)was not directlydetectableinshorebirdnumbersinnorth-westWesternAustralia. Whiletherehasbeena
reductioninshorebirdnumbersatthenorthernendofEighty-mile Beach,thepatternofdeclinewas constantandnotobviously relatedtothetimingofmajordevelopmentsintheYellowSea. Thismaybe a consequence of the impacts of reclamation being partially buffered by increased use of less productive,alternativestagingwetlands.
CONTENTS
EXECUTIVESUMMARY
1. INTRODUCTION
2.SITEDESCRIPTIONS
3.METHODS
3.1 MYSMA Data
3.1.1. Summer
3.1.2.Winter
3.2.Combined MYSMA –BA Data
3.2.1. November Counts of Eighty-mile Beach
3.2.2. Long-term Counts of Eighty-mile Beach
3.2.3.NovemberCountsof RoebuckBay
3.2.4.Long-termSummerCountsof RoebuckBay
3.3.Analyses
4.RESULTS
4.1.MYSMA Data
4.1.1.Summer
4.1.2.Winter
4.2.Combined MYSMA –BA Data
4.2.1.EightyMileBeach
4.2.2.RoebuckBay
4.3.Long-term Data
4.3.1.Eighty-mileBeach
4.3.2.RoebuckBay
4.4.Limits ofAcceptable Change
4.4.1.Eighty-mileBeach
4.4.2.RoebuckBay
5.DISCUSSION
5.1.TrendsinShorebird Numbers
5.1.1.Eighty-mileBeach
5.1.2.RoebuckBay
5.1.3.North-westWesternAustraliaandFlywayPopulations
5.2.Ecological Character of Roebuck Bay andEighty-mile Beach
5.3.Causes of Shorebird Decline
5.4.Monitoring
6.ACKNOWLEDGMENTS
7.REFERENCES
1. INTRODUCTION
Apartfromtheintrinsicinterestinhowshorebirdsnavigateandstorethenecessary energy,thelong distancemigrationsofshorebirdshavehighlightedthatspeciesconservationoftendependsoninter- government cooperation, with failures to conserve in one country resulting in population loss in another. Consequently,shorebirdsarethesubjectofthreebilateralagreementsinvolvingAustraliathat areaimedatachieving habitatprotection andspeciesconservation. ThesearetheJapan-Australia Migratory BirdAgreementsignedin1974,theChina-AustraliaMigratory BirdAgreementsignedin1986 andthe RepublicofKorea-AustraliaMigratoryBirdAgreementsignedin2007. Migratoryshorebirdsare alsothefocusofamultilateralagreement,theEastAsian-AustralasianFlywayPartnership,signedin
2006,whichinvolves10countries,includingtheRussianFederation.
Overthepasttwodecadestherehasbeenincreasingconcernthatthepopulationnumbersofmany migratoryshorebird speciesaredecliningasaresultofreduction inavailablehabitat(Gosbelland Clemens2006;Nebeletal.2008). Whilepopulationdeclinehasbeenobservedinthefewspeciesof residentAustralianshorebirdsand otherwaterbirdsinAustralia(Kingsfordetal.1999),the international obligations on countries to maintain habitat for migratory shorebird species has meant that the potentialpopulationdeclinesofthesespecieshaveprobablyattractedmoreattention.
Thisreportexamineswhethertheremayhavebeenrealdeclinesinnumbersofmigratoryshorebird speciesattwoRamsarsitesinnorth-westWesternAustralia:Eighty-mileBeachandRoebuckBay. The ConventiononWetlandsofInternational Importance(morecommonlyknownastheRamsar Convention)wassignedin1971anditspurpose istopromoteconservationofwetlandsandtheirbiota. Mostcountriesaresignatories. ThebestknownaspectoftheConventionistheListofWetlandsof InternationalImportance,whichisalistofwetlandsnominatedbynationalgovernmentsasbeingof outstandingimportance. Nominatedwetlands mustmeetatleastoneofaseriesofnominationcriteria andsignatorycountriesmustreportontheecologicalcharacterofthesewetlands. Substantialchange ofcharactermayresultinawetland beingremoved fromtheList. BothEight-mileBeachandRoebuck Baywerenominated totheListofWetlandsofInternationalImportance bytheAustralianGovernment in1990.
North-westWesternAustralia supportsmorenon-breedingmigratoryshorebirdsthananyotherareaof AustraliaandisoneofthemoreimportantareasforshorebirdsintheEastAsia-AustralasianFlyway. EightyMileBeachandRoebuckBaycontainthemajorconcentrationsofmigratoryshorebirdsinnorth- westWesternAustralia. IthasbeensuggestedthatshorebirdshavedeclinedatEighty-mile Beachover thelastdecade(Rogersetal.2009). Thechangeshavebeenattributedtoglobaldeclinesinthe numbers ofmanymigratory shorebird speciesandithasbeeninferredthatasignificant amountof declineisassociatedwithareductionintheareaoftidalflatsintheYellowSea. Thesemudflats between KoreaandChinaareusedasstagingareasduringannualmigrations. Themainshorebird counting program at Eighty-mile Beach and Roebuck Bay, the Monitoring Yellow Sea Migrants in Australia program (MYSMA), has included focus on the Great Knot because north-west Western Australiaisthestrongholdofthespeciesinthenon-breeding seasonandbecauseespeciallygrave declineofthisspecieshasbeenpredictedasaresultofhabitatlossatSaemangeumandotherYellow Seaestuaries(Rogersetal.2009).
UnderArticle3.2oftheRamsarConvention,theAustralianGovernment isrequiredtokeepitself informedofanychangeintheecologicalcharacteroflistedRamsarwetlandsandreportthemtothe
RamsarBureau(NRMMC2009). IftheGovernmentisadvisedofapotentialchangetoasite,andan initial investigationsuggeststhematterwarrantsfurtherattention,the Departmentof the Environment, Heritage,WaterandtheArts(DEHWA)willundertakeaformalassessmenttodetermine:
•Thenatureofthechange(i.e.ithasalreadyoccurred,isoccurring,orwillpotentiallyoccur).
•Whetherthechangecanbesubstantiatedonthebestavailablescience.
•Whetherthechangeisa human-inducedadversealteration.
•Whetherthechangehasoccurredina criticalcomponent,processorbenefit/serviceofthesite. Theanalysespresentedinthisreportre-examinewhethertherehasbeenanydeclineinshorebirduse
ofEighty-mileBeachandRoebuckBayandseekstodeterminewhetherthedeclineislikelytobe
attributable tolandusechanges,pollutionorotherhumaninterferencewithinthetwoRamsarsitesor whetherismorelikelyattributable tooveralldeclinesinFlywaypopulations ofmigratoryshorebird species. Inparticular,theanalysesuseddatafromtheMYSMAprojectandtheBirdsAustraliadatabase (includingAustralasianWaderStudiesGroupcountsandShorebird2020Projectcounts)to:
•Investigatewhetherstatisticallysignificantchangeshaveoccurredinthenumbersofmigratory shorebirdscountedatEighty-mileBeachandRoebuckBay,andinparticularwhethernumbers ofGreatKnotandRedKnothavechanged.
•Determinewhether the ecologicalcharactersof RoebuckBay and Eighty Mile Beach have changedsincetimeoflisting.
•Determinepossiblecausesofanydeclinesobservedinmigratoryshorebirdnumbers,including whetheranydeclinesmaybearesultofhabitatchangeatstagingareasintheYellowSea.
ResultsofanalysesofpopulationtrendswereinterpretedinthecontextoftheLimitsofAcceptable Changerecognizedforshorebirdsintheecologicalcharacter descriptions forEighty-mile Beachand RoebuckBay. ThereisasinglewaterbirdLimitofAcceptableChangeatRoebuckBay:“totalwaterbird abundanceinearlyNovember>99400(i.e.75per centofmeanofNovembercounts,dependentoncounting technique)”(Bennelongia2008). ThewaterbirdlimitsofAcceptableChangeforEighty-mileBeachare morecomprehensive:“countsinthearea0-60km…shorebird numbers >200,000duringsummerand
>20,000duringwinter.” Thresholdswerealsosetforfivespeciesinthearea0-60kminsummer:Bar- tailedGodwit>35,000,GreatKnot55,000,GreaterSandPlover>23,000,Red-neckedStint8,000, TerekSandpiper> 4,800(HaleButcher2009).
2.SITEDESCRIPTIONS
Despiteitsname,EightyMileBeachactuallyextendsas alinearbeachfor some225 km (140miles)from
CapeMissiessyinthenorth(19°S)southwesttoCapeKeraudren(20°S)(Figure1). Formostofits lengthitcomprises anextensive intertidalareaandnarrowbeach,backedbysanddunesthatgiveway inlandtonarrowcoastalplains. Inthesouthern partofthebeachthereareoccasional smallrocky outcropsand,inthe section160-165kmsouthof CapeMissiessy,acontinuouslowrockycliff abutsthe mudflats. Therearenomangroves exceptforafew1-2mhighbushesinasmallcreekwherethe MandoraMarshdrainsintothesea.All ofEighty-mileBeachiswithintheRamsarsiteboundary.
Figure1.LocationofRamsarsiteandregularlycountedsectorsofEighty-mileBeach.
CountsonEighty-mileBeachwereusuallymade(andrecorded) in5kmsectorsoftheBeach. The numberingsystemforthesesectorsisbasedaroundtheaccesstracktotheBeachfromAnnaPlains stationhomestead,about20 kmsouthof CapeMissiessy.Thus,thefirst5km sectorsouthof theaccess trackis0-5km,thesecond 5-10km,andsoon. Theareatothenorthoftheaccesstrackhasrarely beencountedandthesectorsarerecordedwithnegativenotation,i.e.thefirst5 kmnorthis0– -5km.
RoebuckBayisalargemarineembayment withveryextensivemudflatsontheeasternside,especially aroundBushPointatthe southernextremity(Figure2). Thenorthernshoreconsistsofaseries ofsmall sandybeachesbackedbylowcliffsofpindansand,withisolatedrockyoutcrops andafewmangrove plants onthebeachandabroadmudflat. Theeasternshoreisfringedbymangroves,withsaltmarshon thelandwardsideofthemangroves, behindwhichisalargeareaoflow-lyinggrasslandsubjectto floodingaftercyclones.Whiletheeasternshoreisused extensivelybyforagingbirds,theyusuallyroost (andarecounted)on the northernshorelineoratBushPoint.Themostwesternportionof RoebuckBay (includingQuarryBeach)isoutsidetheRamsarsiteboundary. However, shorebirds treatRoebuckBay (oratleastthenorthernshoresoftheBay)asasingleareaandshorebird counting overtheyearshas beenalignedwiththepatternofshorebirdoccurrenceratherthatwiththeRamsarsiteboundary.
3.METHODS
Shorebird countswerecompiledfromthreesources:theMYSMAdatabase compiledbyDannyRogers, theBirdsAustraliadatabase, andasetofdataprepared forthisreportbyKenandDannyRogers. Rob Clemens extracted the data used from the Birds Australia database. Backgroundinformationon countingmethodsisavailableinRogers(2005)andRogersetal. (2009).
Priortoanalyses, allspeciesotherthanmigratoryshorebirdswereremoved fromthedatasets.Oriental
Plover,OrientalPratincoleandLittleCurlewwerealsoremoved(exceptwhereexaminingLimitsofAcceptable Change) becausethesespeciestendtoforageinlandandtypicallyroostonbeaches onlyin timesofhotweather(Rogersetal.2009).
Figure2.LocationofRamsarsite,someofthesectorscountedandlandmarksatRoebuckBay.
3.1 MYSMA Data
3.1.1. Summer
TheMYSMAdatasetforshorebirdscountedatEighty-mileBeachandRoebuckBayeachsummerand
winterbetween2004and2009isbasedonaseriesofgroundcountsatdifferentsectorsofbeach. Thereweretwocountseachsummer,onetofourweeksapart,andoneortwowintercounts. The sectors5–40kmofEighty-mileBeachwerecountedconsistently insummer,thesectors40–60km werecountedmostofthetime,andthesectors60–80kmwerecountedin2001and2009. Other sectorswerecountedsporadicallyandarenotincludedinanalyses.
ThedatasetsprovidedtoussuggestthattheonlysectorofRoebuckBaycountedconsistentlyduring summersurveyswas QuarryBeach (lackofconsistencywas morepronouncedwhenBirdsAustraliadata wereincludedinanalyses).However,weweretoldthisreflectstheway datawereentered,ratherthan countcompleteness, andithasbeenassumedthatextractingsurveycountsforallsectorsofthe northernshorewithdataforanysurveywillprovideacountforthewholenorthernshoreinthat survey.
SummercountsweremostlymadeinNovember orDecember, afterbirdsthatwouldcontinue southwards migrationhadmovedthroughnorth-west WesternAustralia,andnumberswere representative ofpopulationsizesatEighty-mileBeachandRoebuckBaythroughtheaustralsummer. However,thefirstcountinsummer2008(theAcount)wasmadeinlateOctober,whenpassage migrantswerestillpresent,andthenumberofbirdsrecordedwasmorethan3standarddeviations abovethemeanofthe12MYSMAsummercounts(Figure3). Subsequent validationofthedata suggested theprincipalreasonforthehigh2008Awasthatsomeofthecountswereduplicatedinthe dataset,ratherthanthenumberofbirdsbeingparticularly high. However, the2008Acountwas removed fromanalyses (ratherthantryingtocorrectthedata)becauseitwaslikelytobe unrepresentativeofsummerconditionsandithadhighleverage.
3.1.2.Winter
Onlyin2006and2007weretwocountsmadeduringwinter,soanalyses ofwinterdatawererestrictedtothefirstsurveydateeachyear. ConsistentcountingoccurredonlyatEighty-mileBeachandthe winteranalysisofMYSMAdataisrestrictedtoEighty-mileBeach.
3.2.Combined MYSMA –BA Data
TheBirdsAustraliadatasetcontainsshorebird countsfromnorth-westWestern Australia datingbackto1983butthedatabasecustodiansandthoseinvolvedinpreviousanalysessuggestthatcountspriorto1999hadvariablemethodologyandoftenindeterminatespatialcoverage,sothattheyaredifficulttouseinanalysisofpopulationtrends(RobClemens,pers.comm.). Furthermore, thecountsmade between1993and2000forthe PopulationMonitoringProgram(PMP)wereundertakeninFebruary.In2001,thecountingdatewasshiftedtoNovember because ofperceived problemswithFebruarycounts aftersignificantrainfall(DannyRogerspers.comm.). Wehaverestrictedanalysis,asmuchaspossible, tocountsmadeinNovember andhaveexcludedsummerdatafromFebruary exceptforparticular analyseswherelong-termtrendswereexamined tovalidatetrendsobserved inNovembercountssince2001.
Inordertoobtainanestimateofshorebirdpopulationsizespriorto2004(bywhichtimesignificant changeswereoccurringattheYellowSeatidalflats),welookedatcombiningtheMYSMAdatawith BirdsAustraliadatabetween2001and2004.TheBirdsAustraliadatasetcontainsfewcountsfrom winteronEighty-mile Beachandsowecombined onlysummerdataforthisRamsarsite,althoughdata frombothseasonswerecombinedforRoebuckBay.
3.2.1. November Counts of Eighty-mile Beach
AdditionalBirds Australiacountswereavailablefor Eighty-mileBeachin 2001and2002,thefirstcoveringallsectorsfrom10-200km(covered80per centofBeachbutcalledatotalcount)andthesecond covering5-40km. Ithasbeensuggested thatsomespecies,especially RedKnot,haveshifted southwardsonEighty-mileBeach overthelastdecadeand,toexaminewhetherpopulationtrendswere consistent indifferentsectorsoftheBeach,wedividedthe5–80kmsectorsintothreegroups:5–40 km,40–60kmand60– 80km.Weusedthesecondsummer(i.e.B)MYSMAcounteachyear.
3.2.2. Long-term Counts of Eighty-mile Beach
Adatasetforanalysis oflong-termtrends inkeyshorebirdspecies atEighty-mileBeach wasprovidedby
DannyandKenRogers. Thisdatasetoflong-termsummerandwintercountswasbasedonsurveysof thesector5–15km,whichhadbeencounted mostyearsfrom1993aspartoftheAWSG’s Population Monitoring Program (PMP) countsand, after 2003, as MYSMA counts. Countsofall migratory shorebirdswerenotavailable.
3.2.3.NovemberCountsof RoebuckBay
Thetrendacrossyearsinsummerbetween2001and2009wasexaminedusingtheBcountsforthe
northern shorefromtheMYSMAdatasetfrom2004to2009andthenorthern shorecountsfromthe BirdsAustraliadatasetfrom2001to2004. Theaverageofthetwo2004counts,whichweremadea weekapart,wasusedinanalyses.
3.2.4.Long-termSummerCountsof RoebuckBay
Adatasetforanalysisoflong-termtrendsinshorebirdsatRoebuckBaywasprovidedbyDannyandKenRogers.Foraboutone-thirdofspecies-datecombinations,wewereunabletoreproducethecountstheyprovidedusingthedatasetwehadobtainedfromBirdsAustralia.Thedatasetwasbasedonsurveysof thenorthernshorefrom1982insummer,and1993inwinter,to2009aspartofthePMPandMYSMAprograms.
3.3.Analyses
Foreachareaandtimeperiod,uptothreecorrelationswerecalculatedforshorebirdnumbersagainstcalendaryear.Shorebirdgroupsanalysedwere:
1. Allmigratoryshorebirdspecies otherthanOriental Plover,Oriental PratincoleandLittleCurlew.ForanalysesoftheMYSMAdataalone,GreatKnotandRedKnotwerealsoexcludedfromthe countofall migratoryshorebirds.
2. Selectedspeciesofmigratoryshorebirdexpectedtoshowdecline(Rogersetal.2009). These wereGreatKnot,RedKnot,Bar-tailedGodwitandTerekSandpiper. TheGreaterSandPlover andRed-necked StintwereincludedinanalysesforEighty-mileBeachbecauseLimitsof AcceptableChangehavebeennominatedforthesespecies.
3. ResidentAustralianshorebirds.ThesewerePiedOystercatcherandRed-cappedPlover.
Inadditiontotheaboveanalyses,numbers ofallshorebirds (includingOrientalPlover,Oriental PratincoleandLittleCurlew)countedatRoebuckBayfrom 2004to2009werecomparedwith theLimits ofAcceptableChangeoutlinedintheecologicalcharacterdescriptionofRoebuckBay(Bennelongia2008).
Numbersofallshorebirds,andnumbersofGreatKnot,Bar-tailedGodwit,GreaterSandPlover,Red- neckedStintandTerekSandpiper, countedinsectors5–60kmatEighty-mileBeachin2001and2009 werecomparedwiththeLimitsofAcceptable ChangeintheEighty-mileBeachecologicalcharacter descriptionforsummercounts(HaleButcher2009). ThesummerLimitsofAcceptableChangeapply tosectors0-60kmbutnodatawereavailablefor0–5km. Insufficientdatawereavailabletomake comparisonswithwinterlimits.
4.RESULTS
4.1.MYSMA Data
4.1.1.Summer
Basedontheaverage ofthetwoearlysummercountsintheMYSMAcounts,thenumbers ofmigratory shorebirdsonthenorthernpartofEighty-mile BeachandonQuarryBeachatRoebuckBayappearto havedeclinedabout7per centperyearsince2004butthedeclineisnotstatisticallysignificant(Figure4). It shouldbenotedthatwiththeexceptionof2008,whenthefirstofthetwocountswasmadeinlate
October(seeMethods),thetwocountseachyearwerewithin17-47per centofeachother,representing similarlevelsofprecisiontothatusuallyseeninshorebirdcounts(Rogers etal.2007). Similarapparent declineswereseeninthenumbers ofGreatKnot(8per cent,Figure5)andRedKnot(10per cent)butneitherdecline wassignificant.
4.1.2.Winter
Aswasthecasewithsummercounts,there hasbeennodiscernabletrendinnumbersof migratoryshorebirdsduringwintersince2004(Figure5). Inaddition,neithertheGreatKnot norRedKnotshoweddiscernabletrends.
Figure3..Numbersofmigratoryshorebirdsatregularlymonitoredsectorsof Eighty-mileBeachand
RoebuckBayinsummer.Averagedcountsshowednotrendacrosstime(outlierexcluded).
Figure4.Numbersof GreatKnotfrom5-40kmatEighty-mileBeachandonthenorthernshoreof
RoebuckBayinsummer.Countsshowednotrend(outlierexcluded).
Figure5.Numbersofmigratoryshorebirdsfrom5-40kmatEighty-mileBeachandonthenorthern shoreofRoebuckBayinwinter.Countsshowednosignificanttrend.
4.2.Combined MYSMA –BA Data
4.2.1.EightyMileBeach
The11per centdeclineinsummercountsofmigratoryshorebirdsattheconsistentlycounted5–40km
sectorsofEighty-mileBeachbetween2001and2009wasgreaterthanthatobservedinMYSMAcounts asaresultofthehigh2001AustralasianWaderStudyGroup(AWSG)count(Figure6). Thetrendof declinewasnotobvious between sectors40–60km. Norwasitobvious between 60and80km, although thesesectorswerecounted onlyin2001and2009. Thus,itisunclearwhethernumbersonall ofEighty-mileBeacharelikelytohavedeclinedbetween2001and2009.
Individual migratoryshorebirdspecies mostly showedsimilar patterns,withGreat Knotcounts declining10per centperyearinthesectors5-40kmbutshowingnochangefrom40-60kmandanapparentsmallincreasefrom60–80km(Figure7). CountsofRedKnotshowedweakevidenceofdeclinebetween2001and2009insectors5-40kmbecause ofthehigh2001count,highlyvariablecounts from40–60 km,andanapparent increasefrom60–80km,suggesting littlechangeoverallinnumbersfrom5–80 km(Figure8).
CountsofBar-tailedGodwitdeclinedabout10 per centperyearinsectors5 - 40 kmandbutshowedno change from40–60km,withasmallapparentincreasefrom60–80km(Figure 9). TerekSandpipershoweda similarpattern, declining by11 per centperyearinsectors5-40kmbutshowingnochangefrom40–80km (Figure10). GreaterSandPloverdeclined by15 per cent peryearinsectors5–40km(Figure11). Incontrast, Red-neckedStint numbersdeclinedabout 8per centperyearinsectors30-60kmbutincreasedabout 30per centper annuminsectors40-60km(P<0.05,Figure12).
Countsfortwospecies ofresidentAustralianshorebirdwereexaminedinanattempttoassesswhether patternsinmigratoryshorebirdabundanceonEighty-mileBeachweredrivenprincipallybylocalfactors. Bothnumbersof Pied Oystercatcherand Red-cappedPloversshowednon-significantincreasesacrossall sectors(Figures13,14).
Figure6.NumbersofmigratoryshorebirdsinsummeratEighty-mileBeach,2001–2009,from30-60 km,40-60km,and60-80km.Numbersdeclinedsignificantlyinsectors5-40km(P<0.01).
Figure7.Numbersof GreatKnotatEighty-mileBeach,2001–2009,between5-40km,40–60km,and
60–80km.Numbersdeclinedsignificantlyinsectors5-40km(P<0.01).
Figure8.NumbersofRedKnotatEighty-mileBeach,2001–2009,from5- 40km,40-60kmand60–80 km.Numbersshowedapparentdeclineafter2001from5- 40km(P<0.10,NS).
Figure9.NumbersofBar-tailedGodwitatEighty-mileBeach,2001–2009,from5- 40km,40-60kmand
60–80km.Numbersdeclinedsignificantlyinsectors5-40km(P<0.01).
Figure10.NumbersofTerekSandpiperatEighty-mileBeach,2001–2009,from5- 40km,40-60kmand
60–80km.Numbersdeclinedsignificantlyinsectors5-40km(P<0.01).
Figure11.NumbersofGreaterSandPloveratregularlymonitoredsitesatEighty-mileBeach,2001–
2009,from5-40km,40-60kmand60–80km. Numbers declined significantlyinsectors5-40km.(P
<0.05).
Figure12.Numbers ofRed-necked StintatregularlymonitoredsitesatEight-mileBeach,2001–2009, from5-40km,40-60kmand60–80km. Numbers declinedsignificantlyfrom5–40km(P<0.01) and increasedfrom40– 60km(P< 0.05).
Figure13.NumbersofPiedOystercatchersatregularlymonitoredsitesatEighty-mileBeach,2001–
2009,from5 -40km,40-60kmand60 –80km.Countsshowednotrendinsectors5-40km.
Figure14.NumbersofRedCappedPloversatregularlymonitoredsitesatEighty-mileBeach,20012009,from5 -40km,40-60kmand60–80km.Countsshowednotrendinsectors5-40km.
4.2.2.RoebuckBay
IncontrasttothenorthernsectorsofEighty-mileBeach,thenumbersofmigratoryshorebirdscountedduringsummeronthenorthernshoreofRoebuckBayfrom2001-2009showednosignificanttrend
(Figure14).Countsofindividualspeciesshowedthesamepatternasallmigratoryshorebirdsandtherewereno trendsinnumbersofanyspeciesonthenorthernshoreduringsummer2001- 2009(Figures15-20).
Figure14.NumbersofmigratoryshorebirdsonthenorthernshoreofRoebuckBay,2001–2009.The
2004valueisaverageofBirdsAustraliaandMYSMAcounts.Trendisnotsignificant.
Figure15. GreatKnotcountsonthenorthernshoreofRoebuckBay,2001–2009.2004valueisaverage ofBirdsAustraliaandMYSMAcounts.Trendis notsignificant.
Figure16.RedKnotcountsonthenorthernshoreofRoebuckBay,2001–2009.2004valueisaverageof
BirdsAustraliaandMYSMAcounts.Trendis notsignificant.
Figure17.Bar-tailedGodwitcountsonthenorthernshoreofRoebuckBay,2001–2009.2004valueis averageofBirdsAustraliaandMYSMAcounts.Trendisnotsignificant.
Figure18.TerekSandpipercountsonthenorthernshoreofRoebuckBay,2001–2009.2004valueis averageofBirdsAustraliaandMYSMAcounts.Trendisnotsignificant.
Figure19.PiedOystercatchercountsonthenorthernshoreofRoebuckBay,2001–2009.2004valueis averageofBirdsAustraliaandMYSMAcounts.Trendisnotsignificant.
Figure20.RedcappedPlovercountsonthenorthernshoreofRoebuckBay,2001–2009.2004valueis averageofBirdsAustraliaandMYSMAcounts.Trendisnotsignificant.
Figure21.NumbersofmigratoryshorebirdsduringwinteronthenorthernshoreofRoebuckBay,1999–
2009.Countsshowednosignificanttrend.
ThenumbersofRed-cappedPloveralsovariedsubstantiallyacrossyears(Figure22).Interestingly,this wasthespecieswiththegreatestdiscrepancybetweenBirdsAustraliaandMYSMAcountsin2004,with theMYSMAcountbeing280per centoftheBirdsAustraliacount.Therewasnosignificanttrendacrossyears.
CountsofallmigratoryshorebirdsonthenorthernshoreofRoebuckBayduringwinteralsoshowedno trendacrossyears(Figure21).
4.3.Long-term Data
4.3.1.Eighty-mileBeach
Long-termpatternsincountsforindividualspeciesatatEighty-mileBeachareconfused. Nospeciesappearstohavedeclinedinabundanceinsummersincetheearly1990sandcountsofsomemigratory species,includingBar-tailedGodwit,haveshownnon-significantincreasesinsummernumbers(Figure22). WintercountsofBar-tailedGodwithavedeclinedsignificantlybutitisoneoftheveryfewspeciestodoso,withhighcountsintheearlyandmid-1990sbeingthelikelycause.
Thenon-significantincreaseof summernumbersof Bar-tailedGodwitmaybe an artefactofcountsprior to2001beingmadeinFebruary(whenfewerbirdsmaybepresentandlogisticaldifficultiesarealso likelytoreducecounts,Rogersetal.2009). However,thefactthat manyspeciesshow paralleltrendsin summerandwintercountssuggeststheFebruarycountsusuallyprovideaccuratepopulation estimates formostspecies(e.g.GreatKnotandRed-cappedPlover,Figures23,25). Anothercauseofpossible unreliabilityinthedataistheshortlength(10km)ofthesectorscountedregularlysince1993. The statisticalpowerassociated withthelong-termsummerdatasetislikelytobelowformostspecies becauseofrelativelyhighvariabilitybetweenadjacentyears.
GreatKnotshowedno trendsineithersummerorwinterbutsummercountswerecyclical,witha return period ofabout10years(Figure23)thatwaspresent, albeitmuchlessclearly,inthecounts ofmost migratoryspeciesinsummerinthe 5-15 kmsector.TerekSandpipercountswereextremelyvariablein bothsummerandwinter.InsummerthisisprobablyassociatedwiththeshortlengthofBeachsurveyed andinwinterwiththelownumbersofbirdsremaininginAustralia(Figure24).
Figure22.CountsofBar-tailedGodwit,1993–2003,atEighty-mileBeach.SummertrendNS,winter trendP<0.01.
Figure23.Countsof GreatKnot,1993–2003,atEighty-mileBeach.SummertrendNS,wintertrendNS.
Figure24.CountsofTerekSandpiper,1993–2003,atEighty-mileBeach.SummertrendNS,winter trendNS.
Figure25.CountsofRed-cappedPlover,1993–2003,atEighty-mileBeach.SummertrendP<0.001, wintertrendP<.05
CountsoftheAustralianresidentspecies,Red-cappedPlover,increasedsignificantlyinbothsummer andwinterwithapproximatelysimilarpatterns(Figure25).
4.3.2.RoebuckBay
ThetotalnumberofshorebirdscountedinsummeronthenorthernshoreofRoebuckBayshowedno
significanttrendfrom1982to2009,withcountsin1982and around2005beinghighrelativetothe rest ofthedataset(Figure26). Matchingtheslight,non-significantincreaseintotalnumbersofshorebirds counted,somemigratoryspeciesincreasedinnumbers.
SummernumbersofBar-tailedGodwitshowednochange(Figure27)but numbersofGreatKnot (Figure
28)andTerekSandpiper(notshown,P <0.05)bothincreasedsignificantly.
Figure26.NumberofmigratoryshorebirdsonthenorthernshoreofRoebuckBayinsummer,1982–
2009.Therewasnotrend.
Figure27.CountsofBar-tailedGodwitonthenorthernshoreofRoebuckBayinsummerandwinter,
1982–2009and1993– 2009.SummertrendNS,wintertrendNS.
Figure28.Countsof GreatKnotonthenorthernshoreofRoebuckBayinsummerandwinter,1982–
2009and1993–2009.SummertrendP<0.001,wintertrendNS.
Figure29.NumberofmigratoryshorebirdsonthenorthernshoreofRoebuckBayinwinter,1993–
2009.Therewasnotrend.Ithasbeensuggestedthe1997countincludesBushPointand,thus,isoutlier, althoughthe2003countwasalmostashigh.
Theoverallnumberofmigratory shorebirds onthenorthern shoreofRoebuck Bayshowednochange between1993and2009.
Individualspeciesshowedfewtrends,althoughinter-annual variabilitywashigh(seeFigure27,28). CountsoftheAustralian residentspeciesincreaseddramatically insummerafter2000andwerevery highinwinter2009,reflectingthepatternatEighty-mileBeach(Figure25)ina morepronouncedway.
4.4.Limits ofAcceptable Change
4.4.1.Eighty-mileBeach
Given thatthethresholdforLimit ofAcceptableChangeinshorebirdpopulationsatEighty-mileBeach is
is1standarddeviationbelowthemeanofcountsonwhichtheLimitofAcceptableChangewasbased,
approximatelyeverysixthcountisexpectedtobebelowthethresholdifpopulationsremainstatic. Thuscountsmustberegularlybelowthethresholdsbeforeabreachoccurs. Nevertheless,itappears thatshorebirdsareapproaching,orhavereached,theLimitsofAcceptableChange atEighty-mileBeach astheyarecurrentlydefined(Table1). Whetherthisrepresentsatruechangeinshorebirduseof Eighty-mile BeachoranartefactofthewaytheLimitsofAcceptable Changehavebeendefinedis unclear.
Table1.SummercountsofshorebirdsatEighty-mileBeachin2001and2009aspercentagesofthe thresholdsforLimitofAcceptableChange.Bar-tailedGodwit,GreaterSandPloverandTerekSandpiper
werebelow thresholdin2009.2001 / 2009
Threshold Count Percentage Count Percentage
Allshorebirds / 200000 / 373887 / 1.87 / 205359 / 1.03
GreatKnot / 55000 / 147364 / 2.68 / 82225 / 1.50
Bar-tailedGodwit / 35000 / 79625 / 2.28 / 27478 / 0.79
GreaterSandPlover / 23000 / 62166 / 2.70 / 18159 / 0.79
Red-neckedStint / 18000 / 19783 / 1.10 / 23709 / 1.32
TerekSandpiper / 4800 / 9562 / 1.99 / 3517 / 0.73
4.4.2.RoebuckBay
ThethresholdforLimitofAcceptable ChangeatRoebuckBayincludeswaterbirds. However, ifitis assumedthat 75per cent of birds present are shorebirds(see Table 23 of Bennelongia2008), then the thresholdfortheLimitofAcceptableChangeallshorebirdsinOctober/NovemberatRoebuckBayis
74,550birds. Thisthresholdwasalmost reached in2006and,toalesserextent,in2007butthereisno indicationthatthetotalshorebird populationisconsistentlyapproachingthethreshold (Table2). Thus, anychangesoccurringinthewaterbirdpopulations atRoebuckBayarewithintheLimitofAcceptable Change.
Table2.SummercountsofshorebirdsatRoebuckBayfrom2004to2009aspercentagesofthe thresholdsforLimitofAcceptableChange(74,550birds).Thethresholdwasalmostreachedin2006.
Count Percentage
2004 / 92764 / 1.242005 / 81343 / 1.09
2006 / 74664 / 1.00
2007 / 77229 / 1.04
2008 / 94440 / 1.27
2009 85007 1.14
5.DISCUSSION
Given thelargeamountofshorebirdobservationandresearchinnorth-westWesternAustraliaoverthe past30years(e.g.MintonMartindale1982;Tulpetal.1994;BarterMinton1998;Battleyetal.
2004,2006;Mintonetal.2006;Rogersetal.2006a),thereissurprisingly littleinformationaboutthe numbersofshorebirdsutilisingthisareaandtrendsinuse. Itwasonlywiththerealisationthatglobal populations ofshorebirds areperhapsdecliningthatpopulation monitoringprograms havebecome prominent andreliablepopulationestimateswillstarttobecomeregularlyavailable(Oldham2007, Rogersetal.2009),althoughperiodicshorebirdcountshave beenmadeatRoebuckBayandEighty-mile
Beachsince1981(Minton2006)andtheAWSGhashadaframeworkforpopulationmonitoringinAustraliasince1986orearlierwithitsPopulationMonitoringProgram(GosbellClemens2006).
TheAWSG’sPMPcountsatRoebuckBayandEightyMileBeachinsummerandwintersince1993appear toprovideinconsistentcoverageofthetwoRamsarsitesbutDannyand KenRogersprovidedsubsetsof countdatafromregularlycounted sectorsforanalysis. Thesecounts(priorto2004andthe establishmentoftheMYSMAprogram)werehighlyvariablebetweenyearsandcountdatesdiffered pre-and post-2001.For thesereasons,statisticalpowerislow inanalysesofthis dataset.Nevertheless, thedirectionofthecountswasgenerallytoshowapparentincreasesinpopulation sizesofshorebirds withtime. Thisisanunlikelyoccurrence,giventhatshorebirdpopulationsaregenerallyregardedas decliningworld-wide, anditismuchmorelikelythatsurveytechniqueshaveimprovedsincethePMP countsbegan. Theapparentincreasesinpopulationsizesareprobablytheresultofbetterorganised surveysthatdetectahigherproportionoftheshorebirdspresentandcountthemmoreaccurately.
ItshouldbenotedwithregardtothePMPcountsofEighty-mile Beachthattheshorebirdcountdata comefromrelativelysmallareaswithineachRamsarsite,andthatanychangesinthedistributions of shorebirdspecies within the wetlands may affect counts. Changes lasting several years, perhaps becauseoflocaldeclinesinpreyabundance (e.g.Bottonetal.1994;Gilletal.2001),maywronglybe interpretedasatrendinshorebirdnumbersataRamsarsite. ThisalsoappliestotheMYSMAcounts madesince2004atEighty-mileBeach. However,monitoringdataformudflatinvertebratessuggests that invertebrateabundanceprobablyincreasedslightlyonthe northernshoreofRoebuckBaybetween2001and2009(Pearsonetal.2010). Invertebrateabundanceshowedorderofmagnitudeincreasesin2009atEighty-mileBeach(mostly becauseofincreasednumbersofOweniidaeworms thatarenotprey items).ThereisnoinvertebrateinformationforsouthernpartsofRoebuckBayorEighty-mileBeach.
5.1.TrendsinShorebird Numbers
5.1.1.Eighty-mileBeach
ThenumberofmigratoryshorebirdscountedatthenorthernendofEighty-mileBeachduringthe austral winter, from5-40km,showednotrend between2004and2009(Figure6). Most keymigratory shorebirdspeciesshowednotrendsincountsduringwinteroverthelongerterm,since1993,inthe sector5–40km. WhileBar-tailedGodwitshowedasignificantdecline,thehighnumberoftestswe carriedoutmeantthatsomesignificantrelationshipscouldbeexpectedbychancealone.
Incontrast,thenumbersofmigratoryshorebirdscountedduringtheaustralsummerinsectors5-40 kmatEighty-mileBeachdeclined11per centperyearbetween2001and2009(Figure6). Thisdeclinewas mirroredinfourspeciesthatwerepreviouslyconsidered tobedecliningbyRogersetal.(2009)(Great Knot,Bar-tailedGodwit,GreaterSandPlover,TerekSandpiper). However,overallmigratoryshorebird numbersandnumbersof GreatKnotappearedtoincreaseslightlyintheadjacentsectors40 - 60kmand
60–80km. ThispatternwassignificantinRed-neckedStint(Figure12). NumbersofRedKnotshowed
notrend. NumbersofthetworesidentAustralian speciesanalysedappeared toincreaseslightlyinthe sector5-40kmbutthesetrends werenotsignificantandtheabsolute numbersofPiedOystercatchers countedweretoosmalltogivereliableinformation. Theoverallpictureoftheseanalyseswasthat,if trendsin shorebirdnumbersinthesector5 – 40kmatEighty-mileBeacharerepresentativeoftrendson theBeachasawhole,therehasbeenadeclineinsummernumbers ofmigratory shorebirds onEighty- mileBeach,withthedeclinesbeingpronounced insomeindividualspecies. However,itisunclear whetherthetrendoccursacrossthewholeBeach.
AsaresultofthedeclinesobservedinthenorthernpartofEighty-mileBeach(0–60km),summer numbers ofBar-tailed Godwit,GreaterSandPloverandTerekSandpiperin2009werebelowthe thresholdsforLimitsofAcceptable Change. Thesignificantdownwardtrendsseeninnumbersofthese speciesin thenorthernpartofEighty-mileBeachsuggeststhesethreespeciesmustberegardedaslikely tobeconsistently underthethresholdinfuturecounts. Itislikelytotalnumberofshorebirdswillsoon alsobeconsistentlyunderthethreshold.
Asalreadymentioned, itispossiblethatbreachesoftheLimitsofAcceptable Changeareanartefactof thresholdsbeingbasedon countsina smallsectionoftheBeach,andthatpopulationsontheBeachasa wholemaynotbedeclining. Sixcounts ofthe whole ofEighty-mileBeach madeduring thelast25years shedlittlelightonthetrendsinshorebirdnumbersatEighty-mileBeach. Thefirstcountof550,000 birds,intheearly1980s(Minton2006),wasbasedonextrapolations fromaseriesofcountsofpartof theBeachandisusuallyregarded asbeinganover-estimate. Anaerialcountaroundthesametimein November 1982 recorded 330,000 shorebirds (Minton 1982). The third count in February 1999 recordedonly53,722shorebirds(BirdsAustraliadatabase). ThefourthcountNovember2001was471,000shorebirds(BirdsAustraliadatabase)andislikelytobearelativelyhighcountintermsof annualvariability,given that the2001countwasaboveany‘trend line’forregularlycountedsectionsof theBeach(Figure6). Thefifthcount,madeinearlyOctober2008fromtheairbyStuartHalseand AdrianBoyle,was262,562shorebirds (RichardKingsford etal.unpubl.data). Thesixthcount,madeon theground sixweekslaterinNovember2008asaShorebirds2020countwas321,137 shorebirds(Birds Australiadatabase). The2008groundcountrepresentsadeclineofabout4.5per centperyearsince2001 whereascomparisonofthe1982and2008Novembercountssuggeststherehasbeennolong-term declineinnumbersatall(ifthatisassumed theaerialcountof330,000ismoreaccurate thanthe extrapolatedcountof550,000shorebirds).
In summary,thethresholdsfortheLimitsof AcceptableChangewerebreachedforthreespeciesin 2009 andpopulation trendsforthesespeciesatthenorthernendofEighty-mile Beachsuggestthebreaches occurconsistently.Availabledatasuggesttotalnumberofshorebirdswillsoonbeinbreachaswell.Itis notclear,however,thatthereisadecliningtrendintheuseoftheBeachbyshorebirdsbecausethe long-term countsshownodecline. Causesfordoubtingthevalidityoflong-termcountsareachange in countingdatesandsmallsurveyareas. Causesfordoubtingthevalidityofthecountsare2001that muchofthetrendisgeneratedby 2001(whichmaybeanunusuallyhighcount)andanapparentcyclical patternofshorebirdabundance, whichmeansthattrendsapparent overfiveorsixyearsmaynot representlong-termpatterns.
5.1.2.RoebuckBay
Thenumberofmigratory shorebirds countedonthenorthshoreofRoebuck Bayduringtheaustral wintershowednotrendbetween2001and2009oroverthelongerterm(Figures21,29).
Thenumberofmigratory shorebirds countedonthenorthshoreofRoebuckBayduringsummeralso showednotrend(Figures14,26). Thispatternwasrepeatedfortheperiod2001–2009inthefour speciesofmigratoryshorebirds analysedindividuallyandalsointhetwospeciesofresidentAustralian shorebirds. Countsofshorebirds inthewholeofRoebuckBayfrom2004to2009haveshownthatthe numberofshorebirdsremainsabovethethresholdforLimitofAcceptableChange.
TheavailabledatastronglysuggesttherehasbeennodeclineinuseofRoebuck Baybymigratory shorebirds.
5.1.3.North-westWesternAustraliaandFlywayPopulations
Giventheconsiderableevidencepresentedoverthepastfewyearsofpopulationdeclineandlossof
shorebirdhabitatintheEastAsian-AustralasianFlyway(GosbellClemens2006;Moores2006;Rogers etal.2006b;Nebeletal.2008),itis surprisingthatthetwoRamsarsitesinnorth-westWesternAustralia noevidenceofshorebirddeclineatRoebuckBayandequivocalevidenceofdeclineatEighty-mileBeach. However,thesesitesarethefirstlandfallsinAustraliaformigratoryshorebirdsonthewesternflight pathoftheEastAsian-Australasian FlywayandRoebuckBayisregardedhighqualityshorebirdhabitat and isextensivelyusedtoaccumulatebodymasspriortothe northwardsmigration(Battleyetal.2004). CountsatRoebuckBayandEighty-mile BeachmaybebufferedfromdeclineinFlywaypopulations becausetheyfilleachyeartocarryingcapacity,withreductions inshorebird numbers occurring onlyat othernorth-westernAustralian,andsouthernAustralian,shorebirdsitesthatconstitutesub-optimal non-breeding habitat(seeEvans1976;Gilletal.2001;Escuderoetal.2003). Thedeclinesobservedin thenorthernpartofEighty-mileBeachin summeroverthelastdecademayindicatethatthislargesiteis notaswellbufferedasRoebuckBay.
5.2.Ecological Character of Roebuck Bay andEighty-mile Beach
ThereisnoevidenceofanychangeinecologicalcharacterofRoebuckBayinrelationtoshorebirdnumbersduringthelast decade.Migratoryshorebirdnumbershaveremainedconstantinbothsummer andwintersince2001.
Thereisclearevidencethat,onthebasisoftheLimitsofAcceptableChangeforshorebirdsdefinedin theecologicalcharacterdescription (HaleButcher2009),Eighty-mileBeachiscurrentlychanging characterbecauseitisbeingusedbyreducednumbersofsomespeciesofshorebirdinsummer. The numbersofmigratoryshorebirdsinwinterdo notappearto be changingandit remainsunclearwhether thedeclinesdetected atthenorthernendoftheBeach,asindicators ofdeclininguseoftheBeach,are valid. Theverylimitedmonitoringofmudflatinvertebrates(Pearsonetal.2010)suggeststhat,ifreal, theshorebirddeclinesdocumentedatEighty-mileBeachreflectreducedFlyway populationsratherthan adeteriorationofshorebirdhabitatatEighty-mileBeach. Thelackofchangesinnumbersofresident Australianshorebirdspecies(infact,non-significantincreases)providessupportforthisinterpretation.
NosignificantanthropogenicchangesatEighty-mileBeachhavebeenreportedandthearearemains verysecluded. ThereispublicaccessonlyforasmallareaaroundtheEighty-mileBeachCaravanPark (Figure1).
5.3.Causes of Shorebird Decline
Giventhelackofevidenceofshorebirddecline atRoebuckBay, andevenatEighty-mileBeach, wehavenottriedtoidentifythecauseofdeclinesinshorebird useofnorth-westWestern AustraliaandthetwoRamsarsites.However,likelycausescanbegroupedintothreecategories:
1. Reducedbreedingsuccess. Breedinghabitatsofshorebirds comingtonorth-west Western Australiaaremostlylocated inremotepartsofeasternSiberia (Minton etal.2006)wherethere hasbeenlittleanthropogenic activity. Whileincreasingtemperaturesmayaffectbreeding success (Hardingetal.2007),itisconsideredunlikely thatreduced breeding success isthemain driverofthedeclinesbelievedtobecurrentlyoccurringinFlywaypopulations.
2. Lossofstaginghabitat. Migrationisenergeticallyexpensiveandmostspeciesrequirestaging habitatsalong themigrationpath wheretheycanfeed andreplaceenergy. Themostimportant stagingareasintheEastAsian-AustralasianFlywayareintheYellowSea. Recentlycompleted and planned development that involves mudflat reclamation around the Yellow Sea is
consideredlikelytocause substantialreductionsinshorebirdpopulations(Moores2006;Rogers etal.2006b).
3. Lossofnon-breedinghabitat. Nebeletal.(2008)haveshownthattherehasbeensubstantial loss ofinlandhabitatforshorebirdsinAustraliaandthat thishas beenassociatedwithmarkedly reducedpopulations ofshorebirdsinlandAustralia. Shorebirdhabitatinmostestuariesin southernAustraliaisalsolikelytohavedeclinedalthoughthisdoesnotappeartohavebeen welldocumented. Theextentoflossofshorebirdhabitatinnorth-westWesternAustraliais less.
Contrarytothepredictions ofRogersetal.(2006b),impactsofbuildingthe33kmseadykeacrossthe tidalflatsatSaemangeumin SouthKoreawerenotdirectlyevidentin thepatternof declineof shorebird numbers,especiallyofGreatKnot,innorth-westWesternAustralia. Thedykewascompletedinearly2006andimpactsshouldhavebeendetectablebytheaustralsummerof2008. Thefailuretodetect impactsofindividualdevelopmentsmaybeattributabletoimpactsbeingpartiallybufferedbyincreased useoflessproductive,alternativestagingwetlands(Gilletal.2001).However,itis likelythat,overtime, Flywaypopulation sizeswilldecreasebecauseofpreydepletionatthealternativestagingsitesand shorebirdpopulationadjustmentsto the lowercarryingcapacitiesof thesesites (see Zharikov& Skilleter2003;Burtonetal.2006). Theprincipaleffectofbuffering maybetopreventimpactsof development beingimmediately obvious. Declineinthenumbersofmigratoryshorebirdsreaching north-westWesternAustraliaappearstobeaninevitableconsequenceofreclamationoftidalflatsin theYellowSea,withassociatedreductioninstaging habitats. Itisexpectedthatdeclinesinthenumber ofshorebirds usingRoebuckBayandEighty-mile Beachwilloccurand,infact,thismayalreadybe happeningatEighty-mileBeach.
5.4.Monitoring
AnalysisoftheshorebirddataforRoebuckBayandEighty-mileBeachhighlightedtheimportanceofregular,long-termmonitoringindeterminingwhethertheecologicalcharacteroftheRamsarsitesis beingmaintained. Suchmonitoring musthavearobustsamplingdesign,consistentcounting methodology (including the same spatial coverage and counting intensity on all occasions) and consistentdatarecording.Monitoringonlypartofa site,whileoftenstatisticallydefensible,reducesthe valueofmonitoring andthecertaintyassociated withmonitoring results. Theanalysesinthisreportof long-termdatafromsmallareashighlightthedifficultiesassociated withitsuse. Futureshorebird monitoringatEighty-mileBeachandRoebuckBayshouldregularlyencompassthewholeofeachsite.
ItisalsoimportantthatshorebirdmonitoringatRoebuckBayandEighty-mileBeachiscomplemented byinformation onFlywaypopulationtrendsandalsobymonitoring ofotheraspectsoftheecological characterofthesetwoRamsarwetlands,suchastheabundance ofmudflatinvertebrates onwhichthe shorebirdsfeed.
6.ACKNOWLEDGMENTS
DannyRogersprovidedtheMYSMAdatasetand,togetherwithKenRogers,putmuchunpaidtimeintopreparingdatasetsforanalysis,aswellasmuchprovidingusefuladviceonshorebirdmonitoringin north-westWesternAustralia.RobClemenspreparedtheBirdsAustraliadatasetandprovidedadvice onthesecounts.BothRobandDannyprovideddetailedcommentsona draftofthereport.
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Appendix1.ShorebirdcountsectorsatEighty-mileBeacharrangedaccordingtocoordinatesinthe BirdsAustraliadataset.Notethatsectornameshavebeenchangedtomatchthesectornames usedintheMYSMAdataset.