Black Terns Chlidonias niger and Their Dietary Problems in Dutch Wetlands
[摘要] BlackTernsChlidoniasnigerhaveshownadecreaseofwellover90%asabreedingbirdinTheNetherlandsduringthetwentiethcentury.Twohypotheseshavebeenputforwardforthisdecline:thedisappearanceofthefloatingplantWaterSoldierStratiotesaloides,whichusedtobethefavouritenestingsubstrateoftheterns,andadecreaseofavailableinsectfoodforthechicks,notablydragonflies.Botheffectsareattributedtoeutrophicationofsurfacewaters.Reproductivebottlenecksvarygreatlyamongareasandhabitats.Inriverlandscapes,nosignsoffoodshortagecouldbefound,andlossofnestingsubstratehasbeensuccessfullycompensatedforbyofferingartificialnestrafts.Extremelylowfledgingsuccessinmoorsandinlowlandgrasslandsiscausedbyfoodproblems.Inthiscase,artificialraftsarelesssuccessful.Withdecreasedinsectavailability,fishandearthwormshavebecomemoreimportantinthechicks'diet,butthesearelessreliableasafoodsource.Fledgingsuccessgreatlydependsontheamountoffishinthediet.Also,aminimumamountoffishisalwaysneededtocoverthecalciumneedofthechicks.Innorth-easternPoland,therewerenoproblemswitheithernestingplacesorfoodforthechicks.
[发布日期] [发布机构]
[效力级别] [学科分类] 动物科学
[关键词] Starvation [时效性]
