Temporal and spatial abundance of wintering Common Eider Somateria mollissima, Long tailed Duck Clangula hyemalis, and Common Scoter Melanitta nigra in shallow water areas of southwestern Baltic sea

Abstract

More than 76 000 Common Eiders Somateria mollissima, 5000 Long-tailed Ducks Clangula hyemalis, and 5000 Common Scoters Melanitta nigra usually spend the winter in the Baltic Sea of Schleswig-Holstein, FRG. Between November 1986 and April 1992 thirty-one aerial surveys were conducted to document their temporal and spatial abundance in the shallow water areas (< 10 m deep). All three species show strong differences in habitat use of offshore shallow waters and coastal shallow waters . Eiders and Long-tailed Ducks leave the offshore shallow waters in the second half of the winter . In contrast, they utilize coastal shallow waters throughout the winter, but especially as staging sites during spring migration. Common Scoters mostly pass through to spend the winter outside the study area; during spring migration they heavily use the offshore shallow waters . Finally the driving factors for the observed distribution patterns are discussed to describe the function of the Baltic Sea of Schleswig-Holstein for seaducks and its relation to other parts ofthe annual range of seaducks.