Foto: Peter Teune
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FIJN R, LEOPOLD M, DIRKSEN S, ARTS F, VAN ASCH M, BAPTIST M, CRAEYMEERSCH J, ENGELS B, VAN HORSEN P, DE JONG J, PERDON J, VAN DER ZEE E & VAN DER HAM N (2017) Concentrations of Common Scoters Melanitta nigra in the Dutch coastal zone demonstrate the importance of available benthos. LIMOSA 90 (3): 97-117.

In the Netherlands, wintering Common Scoters usually concentrate north of the eastern Wadden Islands, and to a lesser extent in the southwestern Voordelta. In some years however, concentrations are found at other sites. In 2015/16 large numbers of scoters were recorded off the Dutch coast near Bergen/Camperduin. Numbers were estimated from counts of birds flying along the coast, counts of groups visible from the coast and from aerial surveys. Food availability was assessed during a benthos survey in April 2016.
Counts of scoters flying along the coast, probably of birds compensating for drift on the coastal current (daily numbers correlated with the lunar cycle), peaked late March at almost 220 000 in four hours of early morning seawatching (Fig. 1, 2), but it is likely that these numbers comprised repeated sightings of the same individuals. On three other days over 100 000 passing scoters were counted. The maximum number recorded in the aerial surveys was just over 40 000 on 8 April (Fig. 3, 4). This survey was thought to have taken place just after numbers had peaked. We conclude that up to 50000 – 100000 Common Scoters were present in March 2016.
The benthos survey revealed high numbers and densities of several bivalve species at the locations of scoter groups and in sizes that scoters can feed on, especially Spisula subtruncata and Abra alba (Fig. 5-9). In contrast to earlier years, Ensis species were not abundant. It is important to realize that this regular, annual, benthos survey was carried out after a whole winter of scoter feeding.
The absence of disturbance by boats might be an explanation for the location choice of scoters. However, ships were present on at least 45% of days with counts from the shore and often caused disturbance amongst the scoters.
The combination of all available data showed that local rich benthos stocks dominated by Spisula can determine the distribution of scoters along the Dutch coast and attract large numbers of Common Scoters that stage locally for several months.

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limosa 90.3 2017
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