OUWENEEL GL (1976) Summering and moulting Shelducks Tadorna Tadorna in the Haringvliet. LIMOSA 49 (3): 115-122.

Common Shelduck Tadorna tadorna Incidentally during the years 1963-1968 and with high frequency since 1969, observations were made on a concentration summering non-breeding Shelduck on the Haringvliet in the province of Zuid-Holland in the Netherlands. 2. In the Haringvliet a large bank is situated, called the Ventjagersplaat.Figure I shows the area. The Ventjagersplaat lies north of the dike. After the closure of the Haringvliet the tidal difference. was reduced to about 15 centimeters. Usually a part of the banks lies just above waterlevel; there are wide shallow waters round the bank. South of the dike we find tidal mudflats. 3. From October till May there are maximal some hundreds of Shelduck on the Ventjagersplaat. In the second part of May numbers start to increase. Table 1 shows the summer-numbers during the years 1971-1975. The maximal number counted at one day on the Ventjagersplaat is 5600 (25-6-1968). Fig. 2 shows the number of firstyear Shelduck in the concentration. 4. The summering Shelduck prefer to stay in the fresh, tideless part of the area; only some hundreds regularly visit the salt tidal mudflats. It is expected that oligochaetes form the greater part of the food. 5. The majority of the summering Shelduck leave the area just before their wing-moult. It is expected that these birds migrate to the Grossen Knechtsand, the important moulting-place in the Bight of Heligoland. Some hundreds of Shelduck (in 1975 more than 500) spend their wing-moult on the Ventjagersplaat.

[free pdf] [dutch summary]