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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Numbers and distribution of Whooper Swan Cygnus cygnus and Bewick's Swan C. bewickii in Germany in the winter season 2004/05
Auteurs :	Johannes Wahl, Auteur ; Axel Degen, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (130(1) 2009)
Article en page(s) :	1-24
Résumé :	Every five years, Whooper and Bewick's Swans wintering in Europe are counted during an international census in January to update estimates of their biogeographic populations. In Germany, 27,158 Whooper Swans were counted in January 2005 with an estimated total of 29,000 individuals. This constitutes the highest number of that species documented so far, almost doubling the estimate based on a previous census in 1995. The largest concentrations were found along the Baltic coast and the adjacent mainland, as well as inland in the (former) floodplains of the larger rivers (e.g. Oder, Elbe, Weser, Ems). 85% of all birds were aged, showing a juvenile percentage of 14.5%. Mean brood size was 2.53 cygnets per successful pair (sample biased towards NW 1 Germany). There were large regional differences in population change (compared to 1995) and Juvenile percentages, which we discuss with regard to conditions in the breeding grounds and wintering strategies. Sixty percent of all Whooper Swans were allocated to feeding habitats. Most birds were recorded on farmland, with rape (76.3%) dominating as feeding habitat. Winter cereals (9%), aquatic plants (6.3%), grassland (4%) and maize (2.6%) were - overall - of much lower importance, but reached considerable proportions in some regions.3,390 Bewick's Swans were counted in January with an estimated total of 3,600 individuals. Compared to 1995 numbers increased threefold. This was probably due to a very mild first half of the winter with hardly any frost until mid January and an overall shift of the non-breeding distribution towards the northeast. Most of the swans were restricted to only a few sites, with almost half of the January total wintering in the lowlands of the river Ems at the Dutch-German border. Nearly all (98%) of the birds were aged, showing a juvenile percentage of 12.7%. Mean brood size was 1.93 cygnets per Successful pair (sample biased towards NW Germany). For 87% of all birds information on feeding habitat was available. Bewick's Swans were almost exclusively found on farmland, with grassland (42.8%), rape (25.9%), maize (18.2%) and winter cereals (11.4%) accounting for more than 98% of swans allocated to a feeding habitat.Due to a cold spell in early March, preventing further migration, large concentrations of Bewick's Swans were found in northern and northwestern Germany around mid March with an estimated 11,000 being present at that time (7,400 in Schleswig-Holstein, alone). As in January, I the swans largely concentrated at a few sites.Finally the census provided valuable information for future improvements of the national I monitoring of swans. Some simple measures, such as co-ordinated yearly sampling of breeding I success based on Juvenile percentages are discussed in the last section of the paper.

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