KRAAN C, PIERSMA T, DEKINGA A & FEY B (2006) New moulting area for Shelduck Tadorna tadorna in the western Dutch wadden Sea offers plenty of Mudshrimps Corophium volutator and little disturbance.. LIMOSA 79 (1): 19-24.

Most Shelduck of Western Europe are known to migrate to the German Wadden Sea for postnuptial moult of their flight feathers. Concentrations of up to 216,000 individuals, more than 80% of the still increasing total population, occur here. Especially since the last two decades, large numbers of Shelduck also moult in the Dutch Wadden Sea. The Balgzand and Breehorn area is one of the traditional sites, where up to 10,000 birds used to moult. Recently however the Balgzand area held lower numbers of moulting Shelduck. During annual surveys in late summer of benthic fauna in the western Dutch Wadden Sea, the presence of small numbers of Shelduck was noted between 1997 and 2002 around the Ballastplaat, near Harlingen (Fig. 1). In July-August 2003 numbers in this area were so large that we spent some time counting them and collected droppings to determine diet composition. During high tide aerial counts in this area in 2003 and 2004, 12,500 moulting Shelduck were counted, divided in several larger groups. In 2005 this number increased to approximately 23,000. The highest numbers at the traditional sites Balgzand and Breehorst were around 2000-7000 individuals, compared to a maximum number of 9700 in the beginning of the nineties. Therefore birds from Balgzand may have moved to the Ballastplaat area to moult.
      As shown by dropping analysis the ducks only fed on the very abundant Mudshrimp Corophium volutator. No other prey species were found in the droppings. Densities of these Mudshrimps increased enormously since 2000, reaching more than 400 per m2 recently (Fig. 2). The sudden preference of this area for moulting Shelducks is likely to be caused by several environmental features. The Ballastplaat is a very muddy area and not surrounded by a passageway for boats, and therefore relatively free of human disturbance. Furthermore, the nearby island of Griend provides shelter from displacement by storms. The availability of large quantities of high quality food, which is not readily encountered in other parts of the Dutch Wadden Sea, enhances the suitability of the area as a moulting site. Common Shelduck Tadorna tadorna

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