Winter in the Rohrschollen nature reserve is a high point for the overwintering of waterfowl. At this time, close to 41 different species may be encountered along the Old Rhine and the nearby canalised Rhine. They escape the rigours of the climate in the climes where they originate in order to find less hostile temperatures with us and water that has not frozen over where they can feed.

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Overwintering birds

We encounter very common species in great concentrations: Great Crested Grebe (Podiceps cristatus), Cormorant (Phalacrocorax carbo), Mute Swan (Cygnus olor), Greylag Goose (Anser anser), Mallard (Anas platyhrynchos), Gadwall (Anas strepera), Wigeon (Anas penelope), Pochard (Aythya ferina), Tufted Duck (Aythya fuligula), Goldeneye (Bucephala clangula) and Coot (Fulica atra). These 11 species alone may account for close to 96% of the total populations present in the sector over the winter.

Fewer in number but more attractive and spectacular, a number of rare species are the pride and joy of the site as they would be for any overwintering site:

  • Red-necked Grebe (Podiceps grisegena): a regular at the site, present every winter but a maximum of only 2 or 3 individuals.
  • Scaup (Aythya marila): a species quite often "drowned out" among the Tufted Ducks (Aythya fuligula).
  • Velvet Scoter (Melanitta fusca): a marine species par excellence, regularly spotted at the site over the last few years.
  • Smew (Mergus albellus): a very small, shy species.
  • Black-throated Diver (Gavia arctica), Red-throated Diver (G.stellata) and White-billed Diver (G.adamsii)… Occasional species, the latter (by far the rarest of the three) having been seen only once in the last twelve winters (1999).
  • Whooper Swan (Cygnus cygnus): one individual seen only once in the last twelve winters… The species stands out among the Mute Swans (Cygnus olor) owing to the yellow and black colouring of its bill.

Monitoring overwintering avifauna

Right on the Rhine-Rhone migration route, the site is ideally situated along the Old Rhine to accommodate overwintering waterfowl and therefore to count them, which is one of the primary missions in terms of monitoring through the winter months.

From mid-October to mid-March, eleven counts are organised and performed in the sector by the City of Strasbourg every fortnight. They are part and parcel of a general intelligence-gathering policy on overwintering avifauna over the entire City of Strasbourg, which includes counts in other sectors: port basins, oil terminal, north and south port zone, forest lakes in La Robertsau…

The method consists in covering an identical route during each count along the canalised Rhine and the Old Rhine in order to carry out a survey using binoculars and a telescope of all surface water. Each individual present is then identified and counted. Large groups comprising several hundred individuals (Tufted Duck, Mallard and Gadwall) are counted using a manual counter. The entire Rohrschollen Island sector is covered in the day, as are the other sectors, in such a way as to prevent any overlap with an external sector and any movement within the sector, which could falsify the data or lead to duplications.

The results obtained after successive counting campaigns are used to draw comparisons over several years in terms of total or specific populations within the same sector or between different sectors.

Photographs:
Black-necked Grebe © Sylvain HELLIO
Female Tufted duck © Philippe STEPHAN
Coots © Sylvain HELLIO