The main avian population changes concerned the mussel-eating tufted duck, pochard and coot; which currently make up some 80% of all wintering waterbirds at Lake Constance. Stefan Werner, Martin Mörtl and Karl-Otto Rothhaupt from the Limnological Institute at the University of Konstanz; and Hans-Günther Bauer from the Max-Planck Institute for Ornithology in Radolfzell found that the diving ducks and coots deplete mussel populations by more than 90% in water as deep as 11 m each winter. Each bird consumes about 1.4 kg of mussels (fresh mass) per day. At one study site, a shallow lake at Konstanz, the birds removed a total of about 750 tons of mussels per km2 in the course of winter. It is apparent that wintering waterbirds exert a strong top-down effect on the littoral community, but the mussel stocks recover every summer during the absence of their main predators.
Freshwater Biology