Kees (C.J.) Camphuysen & Suzan van Lieshout (2024) Common Scoters Melanitta nigra in the Netherlands (2) – annual cycle, breeding grounds and connectivity in the East Atlantic Flyway. LIMOSA 97 (4): 162-174.

The breeding range of the Common Scoter extends from Iceland, Scotland and Ireland in the west, through northern Scandinavia (Norway, Sweden and Finland) to Central-Siberia. Ringing reports are extremely scarce, despite more than 100 intensive ringing studies, as a result of which the most important breeding areas of sea ducks wintering in the Netherlands are basically unknown. To investigate the origin (breeding areas), migration routes, seasonal dynamics, connectivity and residence times of Common Scoters roosting in the Netherlands, a total of 25 specimens were captured above the Dutch Wadden Sea Islands in 2017 and 2019. 16 ducks were fitted with Argos PTTs, of which 14 instruments continued to function. The Common Scoter spends the winter along the Atlantic coast, in the North Sea and in the Baltic Sea. In its wintering areas, the species has a strong preference for shallow coastal waters and bays, along low-lying, often sandy coasts, where it forms large groups sometimes exceeding 100,000 individuals. The stopping places used by the birds with transmitters were grouped into four regions (Atlantic area, North Sea, Baltic Sea and Russia), per country, and within countries according to fixed stopping places. Occurrences along the English south coast, in the Irish Sea and in northern France (The English Channel, Normandy) were all included in the Atlantic region.
On the basis of only 14 birds equipped with Argos-PTTs, almost the entire known flyway of Common Scoters in Europe was covered, from the Portuguese coastal area in the extreme southwest (~42°N, 9°W) , Irish bays (~52°N, 10°W) in the far west, French, Belgian, German and Danish coastal waters in the North Sea, to the western Baltic Sea (Denmark and Germany), stopping places in Estonia, stopovers in the Gulf of Bothnia, a large number of bays from the White Sea to the mouth of the Ob River (~69°30 N, 73°E) to the suspected breeding grounds in Siberia at 80°E. No connection was found with breeding areas in Scotland, Iceland or northern Scandinavia. A total of six birds (3 adult ??, 3 adult ??) moved to the breeding grounds, all of which were in Russia. The Russian part of the distribution area (>30°E) was reached on May 9 at the earliest and was abandoned on October 28 at the latest. That is exactly the period of the year when average ambient temperatures are above freezing.
Regional movements include short flights and longer distance movements in the North Sea, the Baltic Sea and along the Atlantic coast. The regional movements of the 14 Common Scoters caught in the Netherlands led to 17 different European countries and more than 90 different staging areas. All areas where the ducks spent substantial time were already known in the literature as frequently used staging areas or foraging grounds for Common Scoters. Based on this small sample, only the wintering areas in Northwest-Africa were missed. Also, not a single scoter ended up in Northwest-Europe (Scotland, Faroe Islands, Iceland or the Norwegian Atlantic coast). Three types of regional movements were found: (1) movements within the Southern North Sea itself, (2) movements to feeding grounds in the Atlantic coastal area, and (3) birds using the Baltic Sea area. Apart from the Dutch coastal zone, Danish and German waters proved to be of greatest importance for ducks caught in the Netherlands. By far the most time was spent in the Netherlands, especially in the winter months (October-March), but in late summer, the importance of Dutch waters decreased as German and Danish waters gained in importance. The Atlantic coastal areas appeared to be important for a small number of birds, especially in autumn, while those in the Baltic Sea were mainly important in summer. The regional movements were interesting, because the observed mobility matched well with the long-term results of sea migration counts along the Dutch coast. It was never clear whether these visually observed movements were simple compensations to return to preferred stopping places after drifting, or whether the animals could actually move over considerable distances. Based on a very limited number of birds with transmitters, it can now be concluded that movements can occur throughout the year, not only exchanging one short-distance foraging area for another, but also covering many hundreds of kilometres if necessary. The data suggest that the birds try to obtain or maintain information about the quality of alternative feeding areas by visiting them at least occasionally. Some individuals visited a much larger part of Europe than others. The fact that almost all known, important European stopping places were visited, plus the fact that no birds stayed for long periods in places where they really did not belong, suggests that the implants had at most a limited effect on the behaviour of the ducks.

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