Local Black Tern Chlidonias niger Population Trends in Relation to Nest Platform Provisioning

摘要

ThepopulationofBlackTernsinTheNetherlandsstronglydeclinedintheperiodfrom1950to1980.Inrecentyearsnumbershavebeenmorestable.ThesupplyofartificialnestplatformshassuccessfullyattractedbreedingBlackTerns,and80%nowbreedonplatforms.InthispaperwedescribethedevelopmentinnumbersandbreedingsuccessofaBlackTernpopulationinTheNetherlandsovertheperiod1982a€“2015,whereamplenestplatformshavebeensuppliedovertime.Usingthisdatabasewequestionwhetherwecanincreasethebreedingpopulationbysupplyingplatforms.Weareuncertainwhetherternnumbersrespondedtoanincreaseinnestplatforms,orwhetherresearchersrespondedtoanincreaseinternnumbersbyputtingoutmorenestplatforms.Weanalyse(1)settlementandbreedingsuccessinrelationtonestingsubstrate,(2)thecovariationbetweenbreedingnumbersandplatformnumbersovertimeandspace,and(3)thedensitydependenceofsettlementandbreedingsuccess.Againstthisbackgroundweanalysewhethertheannualchangeinplatformnumbersisfollowedbyachangeinternnumbers,aswouldbeexpectediftherewasacausallinkbetweenthetwo.Weshowthatinourstudyareareproductiononartificialplatformswashigherthanonnaturalsubstrateandthattheternpopulationinthewholestudyareaincreasedoverthestudyperiod.Thisincreaseinnumberswasassociatedwithanincreaseinthenumberofplatforms,asexpectedwhenplatformsaffectternnumbers.Settlementinthefirstyearafterintroductionoftheplatformswashigher,butinlateryearstherewasnocorrelationbetweenannualchangeinthenumberofplatformsandannualchangeinthenumberofbreedingpairs.Wedidnotdetectadeclineinthenumberoffledglingsproducedperpairwithincreasingternbreedingdensity.Inconclusion,althoughthegeneralpatternsuggestspositiveeffectsofplatformnumbersonternnumbers,wearestrictlyspeakingnotabletoshowthatsupplyingnestplatformscausedtheincreaseinthelocalBlackTernpopulationoverthestudyperiod.Theanswerawaitslargescaleexperimentswithcontrolareasandindividuallymarkedbirdstoquantifysurvivalanddispersal.