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Food Habits of Diving Ducks in the Great Lakes
After the Zebra Mussel Invasion


Zebra mussels (Dreissena polymorpha) have reached high densities, especially in Lake Erie and Lake St. Clair (Leach 1993), since their introduction into the Great Lakes in the mid-1980s. Densities of zebra mussels over 700,000/m² have been reported at power plants on Lake Erie (Kovalak et al. 1993) and as many as 342,000/m² on fish-spawning reefs in Lake Erie (Leach 1993).

In Europe, Tufted Ducks (Aythya fuligula), Greater Scaups (A. marila), Common Pochards (A. ferina) and Common Goldeneyes (Bucephala clangula) commonly consume zebra mussels (de Vaate 1991, Olney 1963). In the United States, Mitchell and Carlson (1993) reported that 19 of 21 Lesser Scaups (Aythya affinis) entrained into a power plant in Michigan contained nearly 100% zebra mussels in their esophagi and/or proventriculi. Hamilton (1992a) and Wormington and Leach (1992) found pieces of zebra mussel shell in eight waterfowl gizzards from Lake Erie (four Buffleheads [Bucephala albeola], two Lesser Scaups, one Greater Scaup and one Common Goldeneye). The sample size in that study was small, however, and gizzard data are biased because of differential digestion rates of soft and hard food items (Swanson and Bartonek 1970).

Zebra mussels have the potential to affect waterfowl distribution and abundance (Stanczykowska et al. 1990, Wormington and Leach 1992) in North America. Additionally, the bioaccumulation capacities of zebra mussels (Brieger and Hunter 1993, Busch and Schuchardt 1991, Mersch et al. 1992) may enhance the transfer of contaminants to waterfowl (de Kock and Bowmer 1993). Contaminants can negatively affect waterfowl reproduction (de Kock and Bowmer 1993) and may have secondary effects as a contaminant source for Bald Eagles (Heliaeetus Lucocephalus) and humans. Our objectives were to determine which diving ducks currently consume zebra mussels in the U.S. portion of the Great Lakes and what proportion of their diet is now comprised of zebra mussels.

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