We studied the feeding ecology of Long-tailed Ducks (Clangula hyemalis) in two different marine benthic habitats in the Baltic Sea to determine whether there were differences in diet choice, foraging selectivity, body condition, and bird abundance. Our results corroborate earlier suggestions that Long-tailed Ducks exhibit ecological plasticity in selecting winter habitat and food. The majority of Long-tailed Ducks occurred in hard-bottom habitats where they relied on the bivalve Mytilus edulis; however, some of the population wintered in less productive, soft-bottom habitats where they employed a prey-selective foraging strategy, in which they fed on less abundant, but energy rich, crustaceans. Both strategies were apparently viable, as dissected birds in both habitats were in good body condition and had substantial fat reserves.