Individual Differences in Feeding Habits in a Newly Established Great Egret Casmerodius albus Population: Key Factors for Recolonisation

Ardea

Berend Voslamber²  Maarten Platteeuw¹  Mennobart R. van Eerden¹ 

[1] 1 Rijkswaterstaat Waterdienst, P.O. Box 17, 8200 AA Lelystad, The Netherlands;1 Rijkswaterstaat Waterdienst, P.O. Box 17, 8200 AA Lelystad, The Netherlands 2 present address: SOVON Dutch Centre for Field Ornithology, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands

关键词: Habitat Reconstruction;   

DOI  :  

学科分类：动物科学

来源: Nederlandse Ornithologische Unie/Netherlands Ornithological Union

【 摘 要 】

AfterhavingalmostcompletelyvanishedfromTheNetherlandsbythe19thcentury,fromthe1970sonwardstheGreatEgretisincreasinginnumbersagain,particularlyinthenewlycreatedwetlandofOostvaardersplassen.Duringthefirst25years,therateofre-colonisationhasbeenextremelylow,theresidentpopulationneverexceedingfivebreedingpairs.From2000onwards,however,followingtheextensionofthesurfaceareaofshallowmarshland,thenumberofbreedingbirdsincreasedto45pairs.ThispaperdealswiththefeedingecologyoftheGreatEgretduring1976–99,whennumberswereatalowlevel.Individualdifferencesinfoodchoiceandfeedinghabitswerestudiedinordertogaininsightintothekeyfactorsforestablishingandmaintainingahealthypopulation.Observationsonforagingbirdswerecarriedoutduring1987–92.Thebirdsforagedmostlywithinthereserve.FromMarchtoJulytheypreferredforaginginditches,changingtoReedbordersofshallowpoolsanddrygrasslandsfromAugustonwards.Intheditches,Three-spinedSticklebackGasterosteusaculeatus,othersmallfishesandtadpoleswerethemainprey(91.4%ofallpreyitems).Intheshallowwaterbodiestheegretscaughtalmostexclusivelysticklebacks,andingrasslandsCommonVolesMicrotusarvalis.Onebirdwasobservedfeedingnearfishingboats,takingPerchPercafluviatilisandRoachRutilusrutilusof10–20cmlength.Whenfeedingonsticklebacks,aGreatEgrethadtoforagefor1.5to3hourstofulfilitsdailyneeds.Whenscavengingonlargerfisharoundfishingboatsonly15minutessufficed,buttheenergyexpenditurewaslikelytobehigherduetocommutingflightsandinter-specificcompetitionwithGreyHeronsArdeacinerea.However,forthemajorityofGreatEgretstheshallowandtransparentwaterinditchesandpoolswithahighabundanceofyoungsticklebacksandsomecoveragewithemergentvegetationsprovedtobethemostprofitablefeedinghabitat.ThedecisivefactorunderlyingthespectacularincreaseinrecentyearshasprobablybeenthecreationofclearandshallowfreshwaterpoolsandinundatedgrasslandsintheformerlydryborderzoneofOostvaardersplassen.Theseforaginggroundslieclosetoundisturbedbreedingsites.ThisfindingmayproveusefulforwetlandrestorationelsewhereinTheNetherlands.

【 授权许可】

Unknown