Kestrel)Andofagalliforme(Thered-Leggedpartridge)

CaptivityDietsAlterEggYolkLipidsofaBirdofPrey(theAmerican

Kestrel)andofaGalliforme(theRed-LeggedPartridge)

PeterF. Surai1,*

BrianK.Speake1

GaryR.Bortolotti2

Juan J.Negro3

1AvianScienceResearchCentre,ScottishAgriculturalCollege, Auchincruive,AyrKA65HW,UnitedKingdom; 2Department ofBiology,UniversityofSaskatchewan,112SciencePlace, Saskatoon,SaskatchewanS7N 5E2,Canada;3Consejo

SuperiordeInvestigacionesCientificas,EstacionBiologicade

Donana,41013Sevilla,Spain

ABSTRACT

Thesalientfeatureofthefattyacidprofileofkestreleggscol- lectedinthewildwastheveryhighproportionofarachidonic acid(15.2%±0.7%offattyacidmass,np5)inthephos- pholipidfractionoftheyolk.Kestrelsincaptivityfed onday- oldchickensproducedeggsthatdifferedfromthoseofthewild birdsinanumber ofcompositionalfeatures:theproportion oflinoleicacidwasincreasedinallthelipidfractions; the proportion ofarachidonicacidwasincreasedinyolkphos- pholipidandcholesterylester;theproportion ofa-linolenic acidwasdecreasedinalllipidclasses,andthatofdocosahex- aenoicacidwasdecreasedinphospholipidand cholesterylester. Partridgeeggs fromthe wildcontainedlinoleicacidasthemain polyunsaturateofalltheyolklipidfractions.Captivepartridges maintainedonaformulateddietveryrichinlinoleicacidpro- ducedeggswithincreasedlevelsoflinoleic,arachidonic,and n-6docosapentaenoicacidsinthephospholipidfraction;re- ducedproportionsofa-linolenicacidwereobserved inalllipid classes,andtheproportionofdocosahexaenoicacidwasmark- edlyreducedinthephospholipidfraction.Thus,captivebreed- ingofboththekestrelandthepartridgeincreasesthen-6/n-3 polyunsaturateratiooftheyolklipids.

*Correspondingauthor;e-mail:.

Introduction

Theb-oxidationoffattyacidsderivedfromyolklipidsprovides theavianembryowithmorethan90%oftheenergyrequired fordevelopment.Theyolk lipidsarealsothesourceofphos- pholipidandcholesterolforthebiogenesisofcellmembranes. Duringdevelopment,themembranephospholipidsofthedif- ferenttissues acquiredistinctfattyacidcompositions.Forex- ample,the phospholipids ofthe embryo’sbrain and retina becomehighlyenrichedwithdocosahexaenoicacid(22:6n-3), whereasthoseoftheheartandliverdisplayveryhighpropor- tionsofarachidonicacid(20:4n-6).These long-chainpoly- unsaturates arebelievedtoplayessentialrolesinthedevel- opmentandfunctionofthetissuesandcaneitherbe supplied preformedintheyolkorcanbesynthesizedintheembryo fromtheiryolk-derivedC18 precursors. Thus,linoleic(18:2n-6) anda-linolenic (18:3n-3)acidscanbeconvertedto20:4n-6 and22:6n-3,respectively,byelongationanddesaturationre- actions.It is,therefore,evidentthattheyolklipidsmustcontain polyunsaturatesofboththen-6andn-3familiesinamounts andproportionsappropriateforthedemands oftheembryonic tissues.Thecompositionofyolklipidsandtheirutilizationby theavianembryohavebeendescribedinseveralreview articles (Nobleand Cocchi1990;Kuksis1992;Speakeetal.1998a,

1998b;SpeakeandThompson1999).

Thepolyunsaturateprofilesoftheyolkvarygreatlybetween avianspecies,largelyduetodifferencesindiet.Thus,theyolk ofthegranivorouschickencontains18:2n-6 asitsmainpoly- unsaturatesincethisisthepredominantfattyacidofthelipids storedingrainsandseeds(Maldjianetal.1996).Bycontrast,

18:3n-3derivedfromchloroplastlipidsis thecharacteristic polyunsaturateoftheyolk lipidsofherbivorousbirdssuchas thegoose(Speakeetal.1999b)andostrich(Nobleet al.1996). Piscivoressuchastheemperorpenguinproduceeggsenriched with22:6n-3andeicosapentaenoicacid(20:5n-3)duetothe preponderanceofthesefattyacidsinfishlipids(Speakeetal.

1999a).Superimposed onto thesedietaryeffectsarephylo- genetic differencesbetween avianspecies.Forexample,chick- ens,turkeys,ducks,andgeesemaintained onidenticaldiets produceeggswithverydifferentfattyacidprofiles (Maldjian etal.1996;Suraietal.1999).

Severalstudieshavedemonstratedthatcertainavianspecies maintainedincaptivity produceeggswithmarkedlydifferent fattyacidprofilesthanthoseoftheircounterpartsinthewild; forinstance,theyolklipidsofcommerciallyraisedostriches (Nobleetal. 1996),pheasants,andgeese(Speakeetal.1999b)

arerelativelydeficientin18:3n-3,whiletheeggsofducksin captivitycontainexceptionallylowlevelsof22:6n-3(Maldjian etal.1996).Itappearsthatthenaturaldietsselectedbythese birdsinthewildprovidegreateramountsofn-3polyunsatur- atesthanarepresentinthefeedsthatareformulatedforavian speciesincaptivity.Thesuggestionthatthelowhatchability andneonatalviabilitycharacteristicofsomespeciesofcaptive- breedingbirdsmaybeduetoinadequateamountsof n-3fatty acidsintheyolk(Nobleetal.1996)isfeasiblebuthasyetto betestedincontrolledfeedingtrials.

Thereislittleinformationcurrentlyavailablethatdescribes thelipidcompositionofeggsofcarnivorousbirds.TheAmer- icankestrel(Falcosparverius)isanappropriatespeciesforsuch investigationsbecauseitiswidely availablebothinthewild andin captivity(Bird1980).Thered-legged partridge(Alectoris rufa),bycontrast,is largelyvegetarianandisamemberofthe Galliformeorder,whichincludesthedomesticchicken.Captive breedingofthered-leggedpartridgeisanemergingindustry, particularlyinSpain,butnoinformationontherelationship betweendietandeggcompositioniscurrentlyavailable.The aimofourstudyis,therefore,todocumentforthefirsttime thenaturalfattyacidprofileoftheeggsofacarnivorousbird, theAmericankestrel,andtoevaluatetheconsequencesofthe dietsprovidedtokestrelsandtored-leggedpartridgesincap- tivityonegglipidcomposition.

MaterialandMethods

EggCollection

Eggsofwildkestrelswerecollectedin1999fromnestboxes providedforresearchpurposesinthevicinityofSaskatoon, Saskatchewan,Canada.Oneegg per clutchwascollectedwithin

1–2dafteritwaslaid.Eggsofcaptivekestrelswerecollected in1998attheAvianScienceandConservationCentreofMcGill University,Montreal,Quebec,Canada.Thesewerecollected within1daftertheywerelaid,fromacommunalpenhousing

13females(i.e.,thebirdswerenotmated).Thelayingdates indicatethat thefiveeggscollectedwerefromfivedifferent females.Thekestrelsincaptivitywerefedexclusivelyonday- oldchickenshatchedfromeggslaidbyhensfedastandard corn–soybeanmealdiet.

Eggsofwildpartridgesoriginatedfromnestsfoundonag- riculturallandinAndalucia(southern Spain)andwerecol- lectedinMay 1999withpermissionoftheenvironmentalau- thorities.Eggsfromcaptivepartridgeswereobtainedfroma gamefarminAndaluciainAprilandMay1999.Theeggs from boththewildandcaptivitywerecollected1–3dafterlaying, therebyminimizingembryonicdevelopment.Immediatelyon collection,thewholeeggswerefrozenandstoredat—2°C.The yolkwaslaterremovedintactfromtheegg,takingadvantage ofthefactthatalbuminthawsmorequicklythanyolk(Lipar etal.1999).

Captivepartridgesweresuppliedwithacommercialdiet

(containingmaize,wheat,barley,soybeanmeal,andsunflower seeds)formulatedforthisspecies.Thefattyacidcompositions ofthe formulated partridge feedand ofthenewlyhatched chickensfedtothe captivekestrelsareshowninTable1.Frozen yolksamplesofbothspecieswerepacked indryiceandtrans- ported byairfrom Canadaand Spainto thelaboratoryof P.F.SuraiintheUnitedKingdomforanalysis.

Lipid Analysis

Totallipidfromeggyolkwasextractedbyhomogenization inasuitableexcessofchloroform/methanol (2:1,v/v).The massoftotallipidwasdeterminedgravimetricallyonapor- tionof theextractafter evaporationofthesolvent.Themajor lipidclassesintheextract(triacylglycerol,phospholipid,cho- lesterylester,freecholesterol, freefattyacid)were separated bythin-layerchromatographyonsilicagelGusingasolvent systemofhexane/diethylether/formicacid(80:20:1,v/v). Visualization ofthe bands andelutionofthelipidclassesfrom thesilicawereperformedasdescribedpreviously(Nobleet al.1996).Theisolatedphospholipidfractionwasfurthersub- fractionated bythin-layer chromatography on silicagelD usingasolventsystemofchloroform/methanol/acetic acid/ water(25:15:4:2,v/v).Themajor phospholipid classes, phosphatidylcholine (PC),phosphatidylethanolamine(PE), phosphatidylserine(PS),andsphingomyelin,werevisualized andelutedfromthesilica(Nobleetal.1996).

Theisolatedacyl-containinglipid andphospholipidclasses weretransmethylatedtoformfattyacidmethylestersasde- scribedpreviously(Nobleetal.1996).Analysisofthefatty acidmethylesterswasperformedbygas–liquid chromatog- raphyusingacapillarycolumn(Carbowax,30m#0.25mm, filmthickness0.25mm; Alltech)in a CP9001Instrument

Table1:Fattyacidprofilesofthedietsprovided tothecaptivekestrelsandpartridges

Kestrels’DietPartridges’Diet

Ration-6/n-35.3148.0

Note. Values(% w/woffattyacids)aremeans±SEof np4-d-oldchickens(kestrels’diet)ornp4batchesofpar- tridge feed.Total lipid formed 3.6%±0.4%and 4.3%±

0.2%ofthewetmassofthekestrels’andpartridges’diets, respectively.

(Chrompack)connectedtoanEZ ChromDataSystem(Sci- entificSoftware).Thecolumnwasmaintainedat185°Cfor

2min followinginjectionofthesample,then increasedat

5°C/minfor9min,andmaintainedat230°Cforafurther24 min.TheEZChromDataSystemenabledtheexpression of thefattyacidcompositionsintermsofpercentage(w/w)of fattyacidsofthelipidclass.Peakswereidentifiedbycom- parisonwith theretentiontimesofstandardfattyacidmethyl estermixtures(Sigma,Poole)andwerequantifiedbycom- parisonwitha15:0 standard.The amountsofeachlipidand phospholipidclasspresent intheextracts werecalculatedfrom theamountandcompositionofthefattyacylgroupsderived fromeachclasstogetherwiththeacylgroupcontributionto themolecularweightsofthesecompounds.Theamount of freecholesterolintheextractswas determinedusingan enzymatic-colorimetrickitsystem (Boehringer,Lewes).

Statisticalcomparisonbetweenrespectivewildandcaptive sampleswasperformedbytwo-tailedunpairedStudent’st-test followingarcsinetransformationofdataexpressedaspercent- agesinordertomakethevarianceindependentofthemean (SnedecorandCochrane1967).

Results

FattyAcidProfilesoftheLipidClassesinYolksofWildand

CaptiveKestrels

Themajorpolyunsaturatesofthephospholipidfractionofthe eggsfromwildkestrels were20:4n-6followedby18:2n-6(Table

2).Inthetriacylglycerolfraction,18:2n-6wasthemajorpoly- unsaturate,althoughasubstantialproportion of18:3n-3was

alsoobserved.Cholesterylesterwascharacterizedbyahigh contentof18:2n-6withlowerproportionsof18:3n-3and20:

4n-6.Thefattyacidprofilesofyolklipidsfrombirdsincaptivity differedfromthoseoftheirwildcounterpartsinmanyrespects. Inallthreelipidclasses,theeggslaidincaptivitycontained higherproportions of18:2n-6andlowerlevelsofpalmitoleic acid(16:1n-7)and18:3n-3;thephospholipidandcholesteryl esteralsodisplayedincreasedproportions of20:4n-6andless

20:5n-3and22:6n-3comparedwitheggsfromthewild.The proportion ofoleicacid(18:1n-9)was alsoaugmentedinthe cholesterylesteroftheeggsfromthecaptivebirds.Asaresult ofthesedifferences,then-6/n-3ratiowasfarhigherintheyolk lipidsofthecaptivekestrels.

Whileallthephospholipidclasseswererichin20:4n-6,the highestproportionsof22:6n-3werefoundinPEandPS(Table

3).Thetotalphospholipidoftheeggsofcaptivekestrelscon- tainedlessPCandmorePScomparedwitheggsfromthewild birds.ForPCandPE,theeffectsofcaptivebreedingwereto increasetheproportionsof18:2n-6and20:4n-6andtodecrease thoseof16:1n-7,18:3n-3,and20:5n-3;PCcontainedlessof

22:6n-3,andinPStheproportion of20:4n-6wasincreased andthoseof18:3n-3,20:5n-3,anddocosapentaenoicacid(22:

5n-3)werereduced.

FattyAcidProfilesoftheLipidClassesinYolksofWildand

CaptivePartridges

Thephospholipidofeggsofthewildpartridgecontained18:

2n-6asthemainpolyunsaturate,withlower levelsof20:4n-6 and 22:6n-3(Table4).Inthetriacylglycerolandcholesteryl

Table2:Fattyacidprofilesoftheyolklipidsofwildandcaptivekestrels

TriacylglycerolPhospholipidCholesterylEster

Note.Values(%w/woffattyacidsinlipidclass)aremeans±SEofnp5eggs.Totallipidformed29.1%±0.5%and30.1%±

1.2%ofthewetmassofthewildandcaptivebirds’yolks,respectively.Freecholesterolformed3.5%±0.2%and3.3%±0.3%ofthe totallipidmassofthewildandcaptivebirds’ yolks,respectively.

*P!0.001;comparisonwithwild birds’eggs.

**P!0.01;comparisonwithwild birds’eggs.

Table3:Fattyacidprofilesofyolkphospholipidclassesineggsofwildandcaptivekestrels

PCPEPS

WildCaptiveWildCaptiveWildCaptive

%w/wofphospholipid76.0 ±1.469.7±1.8***13.7 ±.813.4 ±.86.5±1.412.0 ±1.6***

Fattyacid:

16:025.9 ±.224.6±.910.7 ±.39.0±.76.0±.97.1±1.8

16:1n-71.3±.0.4±.0*.7±.0.4±.0*.3±.0.2±.0

18:018.5 ±.219.9±.824.5 ±.526.0 ±.523.1 ±.423.9 ±.9

18:1n-916.5 ±.215.4±.79.3±.39.2±.27.6±.67.4±.4

18:1n-72.1±.22.3±.11.3±.11.3±.11.0±.11.2±.2

18:2n-612.5 ±.115.6±.5*7.5±.58.9±.3***6.6±.47.7±.5

18:3n-3.5±.0.0*.8±.0.2±.0*.9±.0.2±.0*

20:4n-614.6 ±.717.7±.8***17.4 ±.422.1 ±.5*20.1 ±.828.9 ±2.7***

20:5n-31.5±.1.2±.0*2.3±.1.3±.0*1.4±.1.4±.1*

22:5n-3.0.0.0.04.1±.21.4±.3*

22:6n-33.6±.21.9±.2*18.2 ±.516.4 ±.923.2 ±1.816.9 ±2.8

Ration-6/n-34.815.81.21.8.91.9

Note.Values(%w/woffattyacidsinphospholipidclass)aremeans±SEofnp5eggs.Sphingomyelinformed3.9%±0.5%and5.1%±

0.7%ofthetotalphospholipidmassofthewildandcaptivebirds’eggs,respectively.Abbreviations:PC,phosphatidylcholine;PE,phosphatidyle- thanolamine;PS,phosphatidylserine.

*P!0.001;comparisonwithwild birds’eggs.

***P!0.05;comparisonwithwildbirds’eggs.

esteroftheseeggs,18:2n-6wasagainthepredominant poly- unsaturate, andsubstantialproportions of18:3n-3werealso observed.Thecholesterylesteralsocontainedsome20:4n-6 and22:6n-3.Theeggsofthecaptivepartridgescontaineda slightlyhigherproportion oftriacylglycerolandalowerlevel ofphospholipidcomparedwiththeeggsfromthewildbirds. Theeggsofthecaptivebirdswerecharacterizedbyincreased proportionsof18:1n-9, 18:2n-6,20:4n-6,and22:5n-6andre- ducedproportionsof 18:3n-3and22:6n-3inthephospholipid fraction.Theproportions of18:3n-3were reducedinthetri- acylglycerolandcholesteryl esterfractionsoftheeggslaidin captivity,andthelevelof22:6n-3incholesterylesterwasalso reduced.Theoverallconsequenceofcaptivebreedingwasto producemajorincreasesinthen-6/n-3ratiointhelipidclasses oftheyolk.

PCcontainedrelativelylowproportionsofthe C20–22 n-6and n-3polyunsaturates,whilePEandPSdisplayedmuchgreater proportionsofthesefattyacids(Table5).Theeggsofthecaptive birdscontainedagreaterproportion ofPCattheexpenseof PS.Inallthreephospholipidclasses,theeggsfromthecaptive partridgesdisplayedlowerproportionsof 18:3n-3and22:6n-3 andhigherproportionsof22:5n-6comparedwiththeeggsof thewildbirds;also,inthecaptivesamples,18:2n-6wasen- hancedinPEandPS,20:4n-6waselevatedinPEandPC,and

18:1n-9wasincreased inthePEfraction.Asaconsequenceof thesedifferences, then-6/n-3 ratioinallthreephospholipid fractionswashigherinthecaptivestate.

Discussion

Thereareapproximately9,000extantspeciesofbirdsadapted toawiderangeofhabitatsandexhibitinggreatdiversityin theirdietarypreferences(Klasing1998;SpeakeandThompson

1999).Dependingon thespecies,birdsinthewildmaybe predominantlygranivorous,herbivorous,frugivorous,insectiv- orous,carnivorous,orpiscivorousormayexploitseveralof thesetrophicmodesincombination(Klasing1998).Eachof thesedietarypatternsprovidesadistinctiveprofile ofpoly- unsaturatedfattyacids;thus,18:2n-6,18:3n-3,and22:6n-3are, respectively, typicalofgranivory,herbivory,andpiscivory (Speakeand Thompson 1999).Feedingtrialsperformedon domesticpoultryhavedemonstrated thatthepolyunsaturate profileoftheyolkislargelyareflectionofthefattyacidcom- positionofthe dietprovidedto thelayinghen,althoughgenetic differencesbetweenavianspeciesalsoplay adeterminingrole (Speakeetal.1998a;Suraietal.1999).Thus,itmaybeexpected thattheyolkfattyacidprofilesofdifferentavianspeciesmay displayahighdegreeofvariationinaccordancewiththeir naturaldietarypreferences.Thedistinctivepolyunsaturatesig- naturesreportedfortheeggsofgranivorous(Maldjianetal.

1996),herbivorous(Nobleetal.1996;Speakeetal.1999b), andpiscivorous(Speakeetal.1999a)birdsareconsistentwith thisprediction.

Themoststrikingaspectof thepolyunsaturateprofileofthe yolklipidsofwild andcaptivekestrelswastheveryhighpro- portionof20:4n-6inthephospholipidfraction.Ineggsofthe

Table4:Fattyacidprofilesoftheyolklipidsofwildandcaptivepartridges

TriacylglycerolPhospholipidCholesterylEster

WildCaptiveWildCaptiveWildCaptive

%w/woftotallipid61.5 ±.263.0 ±.5***31.6 ±.329.4 ±.2***2.6±.43.1±.3

Note.Values(%w/woffattyacidsinlipidclass)aremeans±SEofnp5eggs.Totallipidformed32.4%±1.0%and33.5%±

0.4%ofthewet massofthewildandcaptivebirds’yolks,respectively.Freecholesterolformed2.9%±0.1%and3.2%±0.1%ofthetotal lipidmassofthewild andcaptivebirds’yolks,respectively.

*P!0.001;comparisonwithwild birds’eggs.

**P!0.01;comparisonwithwild birds’eggs.

***P!0.05;comparisonwithwildbirds’eggs.

domesticchicken(Maldjianetal.1996)andofmanywildbirds thathavebeenstudied,includingtheostrich(Nobleetal.1996), pheasant(Speakeetal.1999b),andemperorpenguin(Speake etal.1999a),20:4n-6formsabout5%ofthefattyacidmass oftheyolkphospholipidcomparedwith15%–18%inthekes- treleggs.However,thegull, Larusfuscus,consumingavaried dietinwhichearthwormspredominate,produceseggswitha similarlevelof20:4n-6inphospholipid(Speakeetal.1996b) tothatreportedhereforthekestrel.Inthewild,kestrelscon- sumeavarieddietofsmall mammals,birds,amphibians,and arthropods,althoughthedietconsists almostentirelyofsmall mammalsduringtheperiodofeggformation(Bird1988;Bor- tolotti etal.2000).Theediblepartsofmanyanimalsarea relativelyrichsourceof20:4n-6(Lietal.1998;Taberetal.

1998).Forexample,20:4n-6formsapproximately13%,10%,

11%,and5%,respectively,ofthetotalfattyacylmassofthe liver,heart, brain, and skeletalmuscleoftheadultchicken (PhetteplaceandWatkins1989).Itmaythereforebeproposed thatthehighproportion of20:4n-6intheeggphospholipid ofthekestrelisaconsequenceofcarnivory,althoughcertain invertebratesmayalsocontribute totheintakeofthispoly- unsaturate.

Thebreedingofkestrelsincaptivityresultedinaconsider- able displacementoftheyolkfattyacidprofileawayfromthat observedintheeggsofthewildbirds.Themaineffectswere to increasetheproportions ofn-6polyunsaturates(18:2n-6 and20:4n-6)attheexpenseof then-3fattyacids(18:3n-3,20:

5n-3,and22:6n-3),therebyelevatingthen-6/n-3 ratio.The mainpolyunsaturateoftheday-oldchickensthatwerecon-

sumedbythekestrelsincaptivitywas18:2n-6,anditisfeasible thatthen-6/n-3ratioofthisdietexceedsthatofthepreyitems selectedinthewild.Thereisevidencethatthen-6/n-3ratio ofmeatandparticularlyofadiposetissue fromanimals inthe wildislowerthanthatfromdomesticatedvarieties(Simopoulos

1999).

Theproportionsof20:4n-6and22:6n-3inthephospholipid fractionofeggsofthewildpartridgeweresimilartovalues reportedforthedomesticchicken(Maldjianetal.1996)and forthewildostrich(Nobleetal.1996),pheasant,andCanada goose(Speakeetal.1999b).Themajorpolyunsaturateinall thelipidfractionsofthepartridgeeggswas18:2n-6,withlower levelsof18:3n-3alsopresent.Thedietofthewildpartridgein Spainconsistsofwildandcultivatedgrasses(Graminae)and foragelegumes(especiallyvetchesortares),supplementedat timesbyotherseedsandfruits,andinlatespringinsectsare eaten,especiallyantsandgrasshoppers(CrampandSimmons

1980).Thus,theprovisionof18:2n-6fromtheseeds and legumesplussome18:3n-3fromgrasseswouldappeartobe consistentwiththepolyunsaturate profileoftheyolk,with

20:4n-6and22:6n-3beingsynthesizedmaternallyfromtheir respectiveC18 precursors.

Thepartridgesincaptivityconsumedadietformulatedfrom

cerealgrains(maize, wheat,barley)andseeds(sunflower);this dietwasexceptionallyrichin18:2n-6butcontainedonlyminor amountsofn-3fattyacids.Theeffectofthisdietontheegg lipidswastoincreasetheproportions ofn-6fattyacids(18:

2n-6and 20:4n-6)inphospholipid whilereducingthepro- portions ofn-3polyunsaturates(18:3n-3and22:6n-3)inall

Table5:Fattyacidprofilesofyolkphospholipidclassesineggsofwildandcaptivepartridges

Note.Values(%w/woffattyacidsinphospholipidclass)aremeans±SEofnp5eggs.Sphingomyelinformed3.2%±0.7%and3.5%±0.5% ofthetotalphospholipidmassofthewildandcaptivebirds’eggs,respectively.Abbreviations: PC, phosphatidylcholine;PE,phosphatidylethanolamine; PS,phosphatidylserine.

*P!0.001;comparisonwithwild birds’eggs.

**P!0.01;comparisonwithwild birds’eggs.

***P!0.05;comparisonwithwildbirds’eggs.

thelipidclasses.Again,thisresultedinmajorincreasesinthe n-6/n-3ratio.Mostnotably,theproportionof22:6n-3inyolk phospholipid wasonly1.6%ineggsfromthecaptivebirds comparedwith5.9%ineggsofthewildpartridges.Asimilar lowlevelof22:6n-3intheyolkofcommerciallyrearedducks resultedinareducedproportionofthisfattyacidinthebrain oftheembryowhencomparedwithembryosofwildducks (Maldjian et al.1996;Speakeetal.1996a).Thismayimplythat theyolkofthecaptivepartridgesmayprovideinsufficient22:

6n-3tosupportoptimalbrainfunctioninthehatchling.An- other noteworthyfeaturewasthepresenceofthen-6doco- sapentaenoicacid(22:5n-6)intheyolkphospholipid ofthe captivepartridgessincethisfattyacidisregardedasanindicator of n-3deficiency(Neuringeretal.1988;Anderson etal.1989). Aprobleminherentinascribingacharacteristicyolkfatty acidprofiletoaspeciesinthewildisthevariationthatmay resultfromthediversityofdietaryitemsavailabletodifferent femalesduringvitellogenesis.Ideally,itwouldhavebeenuseful toobtaineggsfromalargenumber offemalestoassessthe extentofsuchvariation.Itis,however,essentialtofollowcur- rent ethicalguidelinesdesignedtominimizethenumber of eggscollectedin the wildand to preventanyreduction in population size.Inthecaseofthewildkestrels,eachofthe fiveeggswasfromadifferentclutch,yetthevariationinfatty acidcompositionwassmall,suggestingthatthedifferentfe- malesinthislocationwereobtainingsimilardiets.Although thereisconsiderableinformationavailabledescribingthefood itemseatenbytheAmericankestrelandthered-leggedpar- tridgeinthewild(CrampandSimmons1980;Bird1988;Bor-

tolottietal.2000),itwouldhavebeen usefultoobtainsamples oftheseitemsforanalysistoprovideadirectcomparisonbe- tweenthefattyacidprofilesofthedietsandeggs.

Inconclusion,thisstudyprovidesthefirstdescriptionofthe effectsofcarnivoryonyolkfattyacidcomposition,supplies additionalsupportfortheconceptthatthecharacteristicdietary strategiesofdifferentavianspecieshaveproducedagreatdi- versityofyolkpolyunsaturate profiles,and presentsfurther evidencethatdietscurrentlyformulatedforbirdsincaptivity maydisplacetheegg’sn-6/n-3ratioawayfromthatwhichis normallyachievedinthewildandwhichinextremecasescould possiblyhavedeleteriousconsequencesforthedevelopmentof theembryoandneonate.Thedeficienciesthatwereporthere maybeparticularlyrelevantforimprovingthenutritionalstatus ofthered-leggedpartridgeraisedincaptivity.Thisspeciesis themainsmall-gamespeciesinSpain,andmorethan2million captive-bredindividualsarereleasedannuallytoreinforcelocal populations(Delibes1992).Red-leggedpartridgesare,however, difficulttobreedincaptivity,partlyduetoahighmortalityof newlyhatchedbirdsintheaviaries(Nadal1992).Thereasons forthismortalityarenotfullyunderstood,butcompositionof thefeedprovidedtothebreederscouldbeafactor.Although therearingofred-leggedpartridgesisbecominganimportant industryinSpain,littleresearch efforthasbeendevotedto improvingthestandardsofcaptiverearing.Thisarticleisthe firstexampleinwhicheggcharacteristicsarerelatedtothe composition ofthefeedprovidedto thelayinghenofthis species.

Previousworkhasshownthateggsofcaptivealligators(No-

bleetal.1993)andostriches(Nobleetal.1996)containreduced proportions ofn-3fattyacidsandalsodisplayagreaterinci- denceofembryonicmortalitywhencomparedwitheggslaid bytheirwildcounterparts,althoughadirectcausalrelationship betweenyolkfattyacidsandhatchingsuccess hasyettobe established.Withregardtothekestrelandpartridge,itwould beofinteresttocomparethehatchabilitiesofeggsproduced inthewildversuscaptivityandtoevaluatetheeffectsofsup- plementingthedietsofthecaptivefemales withn-3fattyacids.

Acknowledgments

Wearegratefulto theScottishExecutiveRuralAffairs De- partment (toP.F.S.andB.K.S.)andtheNaturalSciencesand Engineering CouncilofCanada(toG.R.B.)forfinancialsup- port.RussDawson,KimFernie,IanRitchie,andDavidBird wereinstrumental inprovidingkestreleggs.Wethank Sas- katchewanEnvironment andResourceManagementandthe CanadianWildlifeServiceforpermitsforeggcollection.We alsothankPalomaPrietaandthestaffofthepartridgefarmat LugarNuevo(ConsejeriadeMedioAmbiente,JuntadeAn- dalucia)forprovidingtheeggsofcaptivepartridgesandRafael Villafuerte,directorofInstitutodeInvestigacio´nenRecursos Cinege´ticos, forcollectingtheeggsofwildpartridges.

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