Since the seventies changes in the malacofauna of theWadden Sea near Texel were monitored by the feeding behaviour of seagulls and eider ducks. For instance, shell fragments in their excrements and shells dropped on the dike showed what molluscs they had fed on. Shifts occurred from mussels Mytilis edulis to periwinkles Littorina littorea, Pacific oysters Crassostrea gigas and the American jack knife clam Ensis americanus.