BAPTIST HJM, WITTE RH, DUIVEN W & WOLF PA (1997) Numbers of Eider Somateria mollissima in The Netherlands in winter, 1993-97. LIMOSA 70 (3): 113-118.

Aerial midwinter seaduck-surveys in Dutch inshore waters were conducted annually in 1993-97. In this paper, results of counts of Eider are presented and compared with those of previous aerial surveys of the Wadden Sea and the North Sea coast including the 'Voordelta'. Numbers of Eider in The Netherlands in 1993-97 varied from 120 000 to 170 000, with peak numbers during the cold winter of 1995/96.
      Before 1990, numbers fluctuated between 110000 and 145 000. Nearly all of these occurred in the Wadden Sea. Coastal waters elsewhere had 3500 Eiders at most. In the early 1990s, Eiders in the Wadden Sea faced a food shortage caused by a reduced Cockle Cerastoderrna edule and Mussel Mytilus edulis spatfall, combined with intensive shellfish-fisheries. Considerable mortality of Eiders and a shift in distribution from the Wadden Sea to the Dutch North Sea coastal zone was recorded. I
      n January 1993, less than half of the wintering population stayed at the Wadden Sea. Considerable numbers of Cut trough shell Spisula subtruncata occurred in the coastal zone. As a result, the number of Common Scoters Melanitta nigra increased from a few thousand to over 100 000. The presence of this alternative food supply appears to have been essential for the survival of Eiders. When the food situation in the Wadden Sea recovered, the proportion of the Dutch population wintering there increased to 90% (January 1996). During the cold winter of 1995/96, Eider numbers in Dutch coastal waters were larger than ever before. The Wadden Sea as well as coastal waters north of it were extensively covered with ice. Eiders then concentrated in small patches of open water or were either resting on the ice. Apparently, most birds tried to survive locally, instead of moving south as did Common Scoters. In April 1996, large numbers of starved Eiders were found. In the second cold winter in succession (1996/97), almost 20% of the wintering population was found more southerly.

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