Kees (C.J.) Camphuysen & Suzan van Lieshout (2024) Foraging areas, diurnal rhythms and space use of Common Scoters Melanitta nigra equipped with data loggers in the (Dutch) North Sea coastal zone. LIMOSA 97 (4): 145-161.

To gain a better understanding of aspects such as spatial connectivity and seasonal dynamics of resident Common Scoters in the foraging areas they use, in addition to more traditional observation methods, 25 scoters were captured of which 23 were equipped with data loggers (ArgosPTT’s or GPS/GSM-transmitters). Apart from ecological considerations, concerns about possible harmful effects of sand nourishments on beaches and foreshores and on the fauna living there was an important motivation for the study.
The scoters were captured at night on the open sea using a Rigid Inflatable Boat (RIB) north of West-Frisian Islands. The instruments deployed provided up to 22 months of data in the case of the Argos-PTT’s, and up to 7 months in the case of the GPS/GSM-transmitters. Two of the animals equipped with Argos-PTT-transmitters died within two weeks after implantation. The data from these two animals were not taken into account in the further analysis.
The Dutch coastal area between the isles of Terschelling, Ameland, Schiermonnikoog and Rottum, sometimes up to Borkum (FRG), was by far the most important area in winter months. This was also true for the individuals that returned the following winter. Two other Dutch areas along the Dutch west coast turned out to be important for the tagged ducks: Voordelta (including the Belgian coastal area) and Callantsoog, especially in the spring (April-May). The Wadden Sea itself was used by two individual birds, fitted with a transmitter in the winter of 2019, using three different locations. The nearshore occurrence of scoters off the province of North-Holland appeared to be strongly clustered during the day (06:00- 16:00 GMT), just below the coast, after which the deeper waters were visited in the evening and during the night. The same was found at the West-Frisian Islands and Voordelta, where a strongly clustered occurrence close to the coast during the day gave way to an offshore occurrence during the evening from 23:00 to 07:00 GMT. To gain an overview of the food supply for the birds, the national shellfish stock survey for the Dutch coast in the spring of 2018 was used. (American) Razor Shells were by far the most widespread bivalve species, followed by Cut Through Shells, Banded Wedge Shells and Striped Venus Clams. The mapped distribution of shellfish (biomass, g fresh weight m-2) covered the entire Common Scoter distribution area as deduced from transmitter data and aerial surveys.
The main prey items of Common Scoters found dead in the study area and captured onboard for tagging were Cut Through Shell, Elliptical Surf Clam, Razor Shells and Banded Wedge Shells. The distribution of Common Scoters north of the West-Frisian Islands (based on the transmitter data) suggested that a combination of prey species was decisive (probably mainly Razor Clams and Semi-truncated Beach Shells), but that other factors must also play a role. It was clear, that not all apparently suitable shellfish banks were visited by the tracked scoters and the birds spent considerable time in places where the shellfish abundance was by no means exceptionally rich.

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