Food Consumption of Diving Ducks Wintering at the Coast of South Sweden in Relation to Food Resources

Abstract

The food choice of diving ducks in the nonbreeding season and their exploitation of the potential food resources were investigated in an area on the Scania coast of the Sound (Oresund) in 1965/66 and 1966/67. Aythya maria, A. fuligula and Bucephala clangula occurred commonly in the area together with a few Somateria mollissima, all feeding in shallow water (below 3 m) with Zostera meadows and muddy bottom. 24 A. marila from March and April showed a marked preference for Mytilus edulis in the food. 63 A. fuligula from September-March showed a seasonal variation in the composition of the food related to partly different feeding places in the different months. In autumn and spring Cardium lamarckii and Hydrobiidae spp. dominated the food, whereas Mytilus edulis was more common in December. The exploitation of the food resources of the 410 ha large area was calculated from regular censuses. 172,000-213,000 bird-day units were recorded which, with an estimated consumption of 200 g food/bird/day, equals a consumption of 8-10 g/m2 fresh weight. The consumption by the diving ducks from November to April 1966/67 was about 5 ? 20% of the total decrease in standing crop of potential food species calculated from quantitative bottom samples compared with a total decrease in standing crop of about 70 %. Pe3loMe fnILua HbIPKOBbIX YTOK, HCKJIo'aHH nepHoa BBICH)KHBaHHS rITeHLIOB, H HCHOJIB3OBaHHe HMH BO3MOKHbIX KOpMOBbIX pecypcOB HccJieaOBaJIHCh B paiRoHe mBegcKoro 6epera npOJTIHBa 3peCyHH B 1965-66 R 1966-67 rr. B 3TOM parloHe BCTpe'aIOTCSI Aythya maria, Aythya fuligula, Bucephala clangula H egKHHxIHbie Somateria mollissima KOTOpbIe HWYT KOpM Ha He6oJIbEwo rJIy6HHe (go 3 MeTpOB) c Zostera Hn rniHHHCTbIM J9HOM. B mHle 24 nO11MaHHbIX B MapTe-anpeJIe Aythya marila B 6onbMOM KOJIH'eCTBe 6bur o6HapyxceH Mytilus edulis. B rIMue 63 Aythya fuligula iIOirMaHHbIX OT ceHTI6pH go mapTa 3ame~aiiacb Ce30HHaSI nepemeHa B CBS13H C pa3HL6IMR MeCTaMH KOpMJIeHHS. OceHbIo H BeCHOl upeo6Jiagaim Cardium lamarckiiH Hydrobiidae spp. a Mytilus edulis BCTpeaMJICc 'amie B geKa6pe. H4CnoJIb3oBaHHe nJioUiiaaH giiH II0HCKOB KOpMa B 410 ra BbIC'qlTbIBaJIOCb 6nIarojaps peryRIlpHOR RHBeHTapH3auHH, 6buIO HaCqHTaHO 172,000-213,000 rITnma/,aHei4. B pe3yJIbTaTe 3TO gaeT HpH6JIH3HTeJIbHo 200 r KOpMa B OaHH AeHb Ha OJAHY HTHLY H OTBeC'aeT 8-10 r/M2 CBexcerO Beca. rIOTpe6JIeHHe KOpMa HM6pKOBbIX YTOK COCTaBISeT OCeHbIO OKono 5 HpOueHTOB o6weri 6HoMaccbI Bcex flHTaTeCJbHbIX opraHH3MOB, 3H4MO1 1966/67 o6iuee yMeHbueHue Ha 70 npOUeHTOB 6HoMaccb. Manuscript accepted December 1968.