Foraging behavior and habitat choice of wintering Northern Shoveler in a major wintering quarter in France

The behavior of Northern Shoveler (Anas clypeata) was studied from Septembe r 1996 to March 1997 in four protected areas, one artificial and three natu re reserves, in the Marshes of Rochefort, Western France. Shoveler numbers exceeded the Ramsar criterion of international importance (i.e., 400 indivi duals) during most of the winter. Birds concentrated first at sewage works, showing a diel pattern of foraging depth which could be linked to vertical migrations of crustaceans. Zooplankton density decreased over the winter l eading the Shovelers to abandon the site for natural areas. The two sites w hich hosted most ducks were those where straining the water surface for zoo plankton was the most frequent feeding behavior. At the two other sites, st raining was gradually replaced by deeper foraging, possibly because Shovele rs at least partially turned to benthic invertebrates. This study suggests that food abundance is of crucial importance for winter habitat selection b y Shovelers, and that even the sites with abundant foods in autumn may not be able to sustain large concentrations of Shoveler through an entire winte r. Our results support previous studies which highlighted the importance of some artificial wetlands for the conservation of this duck species. Manage ment options that enhance zooplankton production and, in the event of inver tebrate crashes, the creation of alternative sites at close distance appear to be highly valuable to wintering Northern Shoveler populations.