Distribution, phenology and long term trends of Red Knots Calidris canutus in France

摘要

The two subspecies of the Red Knot Calidris canutus that occur in Europe during northward and southward migration, islandica and canutus, are only observed simultaneously at a few sites such as the Wadden Sea. Mostly islandica winters on estuarine bays in NW Europe, while canutus go to wintering grounds in W or S Africa. The coasts of France have been described as the main southern limit of the winter distribution of islandica and as providing stopover sites for canutus migrating between the W African coast and breeding grounds in Siberia. Nevertheless, the role and the importance of French sites remain unclear for both subspecies, especially during southward migration. This study updates information on the numbers and the distribution of Red Knots staging or wintering along the coasts of France using International Waterbird Census (IWC) data (counts carried out in Jan, 1976-2010, organised by Wetlands International) and synchronized monthly counts carried out in France's National Nature Reserves during 2000-2010. In recent years, France has supported around 9% (c.35,000 individuals) of the estimated population of islandica in mid-winter. Ninety percent of these birds are concentrated in just six bays, two along the Channel coast and four along coasts of Vendee and Charente-maritime. As intertidal areas are limited along the Mediterranean shore, it does not support Red Knots in winter. Numbers of islandica peak in mid-winter, but significant passage of canutus occurs in May on the central Atlantic coast. Patterns of autumn migration remain unclear and information on occurrence of both subspecies is lacking. Long term trends in site use differ from place to place; this is probably an indication that they are used by birds of different origin and age.