Isotopeforensicanalysis doesnotsupport vagrancyforaMarbled DuckshotinEssex
Tony(A.D.)Fox,KeithA.Hobson,GrahamEkins, MarkGranthamandAndyJ.Green
Abstract Analysisofthestable-hydrogenisotopecontent(δD)offeatherstaken from a first-winter Marbled Duck Marmaronetta angustirostris shot in Essex on 1st September 2007 showed little difference between juvenile feathers grown at the natalsiteandthosegrownduringthepost-juvenilemoult.TheδDvaluesofboth groups of feather were similar to those expected if the bird had grown feathers in coastalareasofnorthernEurope,butdifferedsignificantlyfromthoseinfeathers fromknownwildindividualstakenfromthespecies’nearestbreedingareas,in Spain.Theseresultssuggestthatthebirdoriginatedfromoutsideofthenormal breeding range of the species and was most likely to have been of captive origin.
hestable-hydrogen isotoperatio(D/H or2H/1H,conventionallyexpressedas δD)inbirdfeatherscorrelatesstrongly
(through localdiet)withthatofweighted averageprecipitationintheareaswherethe feathersweregrown(HobsonWassenaar
1997;Hobson2008).Deuteriuminprecipita- tiontendstobedepletedwithincreasingdis- tancefromtheoceans,whicharethesource ofatmosphericrechargemoisture,andwith latitudeandaltitude,resultingindistinctive geographical gradients within Europe(Hobsonetal.2004; Bowenetal.2005;Votier etal. 2009).Becausehydrogeninconsumer tissuescanultimatelybetracedtoenviron- mentalwatersdrivingfoodwebs,thepattern of δD in weighted averageannual (orgrowing-season)precipitationcanbeusedto helpidentifytheisotopicenvironment in whichabirdhasgrownspecificfeathers. In turn,thiscanassistinestablishinggeograph- icalrelationshipsbetweentheareasusedby anindividualthroughouttheyear.Inthecase offirst-yearbirdsthatretainsomeoriginal
(juvenile)feathers, thiscancontribute to definingthegeneralgeographicalareain whichthebirdwasfledged.
Thisapproachwas usedtoprovideevi- dencethatafirst-winterBaikalTealAnas formosashotinDenmarkinNovember2005 wasagenuinevagranttoEuropebyvirtueof thesubstantial isotopic contrastbetween juvenile feathers(showingstable-hydrogen isotopecharacteristicstypicalofSiberia)and first-winterfeathers(thatweremoretypical ofanoceanic, westernEuropeantypeenvir- onment) onthesamebird(Foxetal.2007). AnanalysisoffeathersfromaBaikalTeal specimencollectedinEssexinJanuary1906 showedverysimilarpatterns,alsoconsistent withthisbeingagenuinevagrantfromthe normalRussianbreedingarea(Votieretal.
2009).
Here,weapplythesametechniqueto investigatethepotentialoriginofafirst- winterMarbledDuckMarmaronetta angu- stirostrisshotatFingringhoeMarshes,near ColchesterinEssex(51°51’N00°57’E),on1st
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September2007.TheMarbledDuckremains inCategoryDoftheBritishListbecause thereisreasonabledoubtthatthespecieshas everoccurredinthewild(Dudleyetal.
2006).Analysingfeatherstable isotopesfrom thespecimencouldprovideevidenceto suggestwhetherthisbirdwashatchedinthe wildandthereforemetthecriterionfor inclusionontheBritishList.Inthisstudy,we analysednew-grownfeathermaterialfrom theshotbirdtoseeiftheresultsmatched withthoseexpectedfromBritishorigins, comparedwitholder(juvenile)feathers growninnatalareas.Wepredictedthat,ifthe birdwasagenuinewildvagrant,thesetwo feathertractswouldshowcontrastingδD valuesandthattheolder featherswouldshow higher(i.e.morepositive)δDvaluesmore typicalofthespecies’Mediterraneanand NorthAfricanbreedingrange.
Methods
Vanesectionsweretakenfromnew-grown scapularsandbreastfeathersoftheEssex MarbledDuck,aswellasold(juvenile)tertial and wing-covert (greaterand median)feathers.Sectionswerealsotakenfrombreast feathers removedfromthreeapparentlywild MarbledDucksfromSpain:(i)adultfemale, recovereddeadatBrazodelEste,Marismas del Guadalquivir, Sevilla
VSMOW-SLAPscalewithareproducibility ofwithin ±3.5‰.
Results
ValuesoffeatherδDfromtheEssexMarbled DuckandfromthethreeSpanishbirdsare shownintable1andfig.1.Differences betweenthemeanδDvaluesfromfeathers takenfromtheEssexbirdandthoseofthe Spanishbirdswerestatisticallysignificant(as shownbynon-overlapping95%confidence intervals).Therelativelydepletedvalues for deuteriuminthefeathersoftheEssexbird morecloselyresembledsimilarvaluesinthe feathersofotherdabblingduckspeciesreportedintheliteratureforcoastalwestern Europe,for exampleMallardA.platyrhynchos fromFrance(Hobsonetal.2004) andBaikal Tealwithfeathersknowntohavebeengrown inDenmark(Foxetal.2007).
Discussion
Isotopicanalysisofthefeathersfromthe EssexMarbledDucksupportthehypothesis thatitwasraisedincaptivitysomewherein coastalareasofnorthern Europeratherthan inthewildinSpainorelsewhereinthe Mediterranean,thenearestareastoEssexin whichthespeciesbreedsnaturally.Therewas nomarkedisotopicdifferencebetweenthe
(37°05’N06°01’W)on 4thAugust1999;(ii) juvenileunsexed,probablyhatchedlocallyandrecovereddeadat ElHondo,Alicante(38°11’N
00°45’W)on3rdJuly2001; and(iii) anadult(unsexed) takenintotherecoverycentre atElHondoon27thJuly2008 butthatdiedthenextday. Prior to isotopic analysis,feathermaterialwascleaned with2:1chloroform:methanol
-40
-60
-80
-100
MarbledMarbledMallardsBaikalTeal DucksDuckFrancefeathers SpainEssex –grown in
natalDenmark feathers
solvent mixture toremove surfacecontaminantsandoils. Cleanedfeathertissueswere thenanalysedforδDusingthe comparative equilibriummethodologydescribed inHobsonetal.(2004).Stable- isotoperatioswereexpressed in ‰ deviation from the
Fig.1. δDvaluesfromMarbledDuckMarmaronetta angustirostris,MallardAnasplatyrhynchosandBaikalTealA.formosa feathersknowntohavebeengrowninEurope.Valuesrepresent means(±95%confidenceintervals);inthecaseofMarbledDucks inSpainthemeanvaluesfrombreastfeathersfromthree
differentindividuals,andinthecaseoftheEssexMarbledDuck themeanoftwovaluesfromjuvenileplumage(tertialandwing- coverts).DataarealsoshownfromMallardfeathersfromFrance (Hobsonetal.2004)andBaikalTealfeathersfromDenmark
(Foxetal.2007).
recentlygrown(first-winter)feathers, which wereexpectedtoreflecttheenvironment wherethebirdwasshot,andtheolder(juvenile)feathersthatwouldhavebeen grownpriortofledgingonthebreeding areas,suggestingthattheseareaswereone andthesame.Furthermore,theδDvaluesof thesefeathersweresimilartothosefrom feathersgrownbyBaikalTealsinDenmark andMallardsinFrance,suggestingamore northerly origin for the fledging andmoultingsitesofthisbird.Comparisonswith feathers from threedifferentSpanishMarbledDucksshoweda meanδDvaluesig-
nificantlygreaterthantheEssexbird(by about20‰).
Aswasthecasewiththeearlierstudies (Fox etal.2007;Votieretal.2009),suchiso- topicanalysescannotprovedefinitivelythat theEssexMarbledDuckwashatchedand rearedincaptivity innorthern Europe.Itis possiblethat thereareMarbledDuckbreedingareaselsewhere,wheretheisotopic signaturesinfoodwebsaremoresimilarto thoseinnorthern coastalEurope,butthis seemsunlikelygiventhatthedeuteriumpre- cipitationbasemaps(e.g.Bowenetal.2005, Votieretal.2009) showsimilarlylow,ifnot lower,meanannual
precipitation δD
valuesfarthereast in the breedingrangeofthespecies compared withthoseofSpainand NorthAfrica. TheMarbled Duck isalso reasonablynumerousincap-tivity,soitseemsmorelikelythatthis wasabirdthatwas raisedinacollec-tion and which escaped before beingshot in thewild. This resultsupportstheuseful- nessofusingstable- isotopeanalysisof feathersforitscon- tribution in con-firming the origins ofrarespecies(wild or captive),espe-ciallywherefeather or other materialcanbe obtainedwithoutcausingthe deathofthebird, but reiteratestheneedfor confirma- toryevidencefrom othersources.This example is lessclear-cut than the
278. MarbledDuckMarmaronettaangustirostris,Spain,April2005.
earlier analyses of
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Table1. δDvaluesfromfeatherstakenfromaMarbledDuckMarmaronettaangustirostris
specimenfromEssexandthreefromSpain(seetextforfulldetails).
Location / Feather / Sitewherefeather assumedgrown / ‰δDEssex / Oldtertials, leftwing / Natal site / -74.8
Essex / Oldmedianand greatercoverts, leftwing / Natal site / -74.0
Essex / Apparentlyfresh breastfeathers / Winterquarters / -70.9
Essex / Apparentlyfresh scapulars / Winterquarters / -76.5
(i)Marismasdel
Guadalquivir,Spain / Breast / SpainorNorthAfrica / -57.7
(ii)ElHondo,Spain / Breast / Spain / -66.5
(iii)ElHondo,Spain / Breast / SpainorNorthAfrica / -46.9
BaikalTeals,wherethestrikingdifferences infeatherdeuteriumexpectedbetweenwesternEuropeandcontinentalSiberiawere thebasisformoremarkeddifferencesin feathermaterial(Foxetal.2007;Votieretal.
2009). Nevertheless,ourstudysuggeststhat the2007EssexMarbledDuckisunlikelyto constitutethefirstdemonstrablerecordof truevagrancyfor thisspeciestoBritain.
Acknowledgments
ThankstoBrianMeadows(whoisnotawildfowlernor involvedwithoriginallyobtainingthebird)forliaison andgainingaccesstotheshotspecimenandtohimand thewildfowlerconcerned forenablingtheanalysisof feathermaterial.ThankstoMarcosFerrandezforhelp supplyingtheSpanishspecimens andtoLenWassenaar forassistance withtheisotopicmeasurementof samples,whichwererunattheNational Water ResearchInstituteinSaskatoon,Saskatchewan,Canada. FundingwasprovidedbyanoperatinggranttoKAH fromtheCanadianWildlifeService.
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Prof.Tony(A.D.)Fox,DepartmentofWildlifeEcologyandBiodiversity,National
Environmental ResearchInstitute,AarhusUniversity,Kalø,Grenåvej14,DK-8410Rønde,
Denmark
Prof.KeithA. Hobson,EnvironmentCanada,11InnovationBlvd.,Saskatoon, SKS7N 3H5, CanadaandDepartmentofBiology,UniversityofSaskatchewan,Saskatoon,SKS7N5E2, Canada
GrahamEkins,35ChurchRoad,Boreham,EssexCM33BN
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Prof.AndyJ.Green,Department ofWetlandEcology,EstaciónBiológicadeDoñana, AvenidaMaríaLuisas/n,PabellóndelPerú,41013Sevilla,Spain
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