Landsat satellite images for detection of submerged macrophytes : on search of potential stop-over feeding sites for Bewick's Swans along their migratory route between arctic Russia and western Europe

Bewick's Swans rely on the roots and tubers of submerged macrophytes, e.g. Potamogeton spp., as an energy rich food resource used to build up the necessary body reserves for autumn migration between the breeding grounds in arctic Russia and the wintering grounds in W-Europe. The exact route and stop-over sites where swans replenish the body reserves are partly unknown, and swans can only cover the total distance with several intermittent stops for feeding. Moreover, no information exists on the availability of aquatic food resources along flyway. LANDSAT satellite images were used to detect areas with abundant submerged vegetation along the flyway of the swans. Nine sites (Lake IJsselmeer / Border Lakes and areas in Poland, Lithuania, Estonia and Russia) were studied. From this study, the preliminary conclusion drawn in earlier feeding studies, that Potamogeton could play a limiting role on swan numbers is carefully confirmed.