Ural Owls Strix uralensis at the Border Line: Nesting Places are Not a Limiting Factor

[摘要] TheUralOwlStrixuralensismeetsitswesternmostdistributioninHedmarkCounty,southeastNorway.Since1979wehaveprovidedthespecieswithnestboxesinthisregion.Atotalof80nestboxeswereputoutinprimeUralOwlhabitat,startingwith9in1979,18in1982and53in1985.Twomorenestboxesputupbyothers,andfourmadebyourselves,werelateradded,givingatotal86nest-boxlocalities.Thenestboxeswerecheckedupto2004,when28nestboxesweremovedtowestern(n=8)andcentral(n=20)Sweden.Wehaveanalysedtheresultsfor25seasonsfrom1980to2004.Forcomparison,theresultsforthe20nestboxesincentralSwedenfortheseasons2005–07havebeenincluded.TheNorwegiannestboxesofferedatotalof1429nest-boxyears.Sinceallboxeswerenotinspectedeachyear,thetotalnumberofobservation-yearswas847(59.3%).UralOwlsonlyused4nestboxesforbreeding,occupiedforthefirsttime1,1,1and10yearsrespectivelyaftertheboxeswereputup.Thefourboxeswereusedforatotalof19breedings.IncentralSweden,9outof20nestboxeswereusedbyUralOwlsforbreeding(n=6)orbreedinginitiations(n=3),foratotaluseof8of56nest-boxyears.TheUralOwlnest-boxuseinNorway(1.3%ofnest-boxyears)isverylowcomparedtocentralSweden(14.3%ofnest-boxyears).TelemetrystudiesofUralOwlhuntingbehaviourin1989–90(unpubl.)showedthatthenestboxeswereindeedplacedinprimeUralOwlhabitat.Despitethis,therewasnoincreaseinUralOwlnest-boxbreedinginNorwayduringthestudyperiod.WeconcludethatUralOwlsarenotlimitedbynestsitesatthespecies'westernmostborderlineandhypothesizethatfoodavailabilityduringwinterisamorelikelyfactorlimitingthespecies.

[学科分类] 动物科学

[关键词] Norway