SWENNEN C & MULDER T (1995) Moulting Shelducks Tadorna tadorna in the Dutch Wadden Sea. LIMOSA 68 (1): 15-20.

In this paper, results of aerial, shipboard and shore-based observations on moulting Shelducks in the Dutch part of the Wadden Sea are presented, adding more detailed observations on abundance and behaviour of flocks of moulting birds near Wieringen (Fig. 1), at the western end of the Dutch Wadden Sea (1988-93). In the early 1990s, a total of about 30 000 Shelducks moulted their flight feathers in the Dutch part of the Wadden Sea during late June through mid-September, with up to 9 700 of these near Normerven, Wieringen (1991, Tab. 1). The number of Shelducks moulting near Normerven decreased during 1991-93 (Tab. 1) due to geomorphological changes of the area. In contrast to non-moulting birds, moulting Shelducks were very shy, swimming in compact flocks during high tide, often on relatively deep water, in stead of resting ashore. When an approaching boat came too close, moulting Shelducks fled by swimming considerable distances under water. Analyses of faeces collected near Wieringen in 1991 revealed that food of flightless adults consisted of Enteromorphaflexuosa mixed with a small amount of dead or resting stems of the hydrozoan Laomedea longissima. Small mollusks and other macrobenthos - comprising most of the diet of Shelducks in this area in spring - appeared to be virtually lacking from areas frequented by moulting birds (1991). Food of Shelducks during the moulting period was low in energy content; their diet then was similar to that of Brent and Wigeon while wintering in this area. Observations suggest that the key factor rendering an area suitable as a moulting place for Shelducks is absence of (human) disturbance; our data on diet suggest that food availability is of secondary importance. Several moulting places are being used by Shelducks in The Netherlands since early this century. The total number of birds moulting in the Netherlands has increased approximately parallel with the overall increase of the entire NW-European population during the last 40 years. The existence of moulting areas in The Netherlands, frequented by a steadily increasing number of Shelducks, should not be considered as an indication that maximum carrying capacity of the major moulting areas in the German part of the Wadden Sea (with 200 000 birds, Nehls et at. 1992) may have been reached. Common Shelduck Tadorna tadorna

[free pdf] [dutch summary]