CONCENTRATIONS OF MIGRANT DIVING DUCKS AT POINT-PELEE-NATIONAL-PARK, ONTARIO, IN RESPONSE TO INVASION OF ZEBRA MUSSELS, DREISSENA-POLYMORPHA

The European Zebra Mussel, Dreissena polymorpha (Pallas), has recently invaded North America and is now well established in Lake Erie. Since 1988, larger-than-usual flocks of eight species of diving ducks were observed at Point Pelee during autumn migration. Maximum one-day count s of the principal species, Lesser Scaup, Aythya affinis, were up to 9 0 times historical counts. The ducks also remained in the area for a l onger-than-normal period. Examination of gizzard contents of eight spe cimens and observations of feeding behaviour indicated that the ducks actively feed on Zebra Mussels. The availability of a new food source has led to this recent change in autumn migratory behaviour by several species of diving ducks. Distribution patterns of diving ducks in oth er areas of the Great Lakes may change as the Zebra Mussel expands its range.