Exploitation of a new staging area in the Dutch Wadden Sea by Greylag Geese Anser anser: the importance of food-plant dynamics

The colonisation by Greylag Geese Anser anser of a new autumn migration sta ging area was studied on the island of Schiermonnikoog, The Netherlands. Ov er 500 Greylag Geese first visited the island in 1991. During subsequent ye ars, peak numbers rose to 700-900 birds. The geese most likely originated f rom the neighbouring staging area on the mainland, the Lauwersmeer, where g oose numbers had levelled off since 1985. Because of the time-lag between s aturation of the source population and colonisation of the island, changes on the island itself were investigated as a possible trigger for the arriva l of the geese. Potential food availability on the island had increased for the geese as a result of vegetation succession. Two food-plants, Sea Club- rush Scirpus maritimus and Common Cord-grass Spartina anglica have increase d over the last four decades. Greylag Geese fed mostly on Scirpus tubers an d Spartina rhizomes. The soluble-carbohydrate content of the latter two foo d items did not differ significantly, and was approximately 25% on a dry we ight basis. Negative effects of grubbing by Greylag Geese on stands of both Scirpus and Spartina appeared limited during the study period. Although Gr eylag Geese now spend most of the year in agricultural areas, our study ind icates that natural habitats are still of importance for migrating Greylag Geese as staging areas.