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Jan Ove Bustnes, Geir Helge Systad, Comparative Feeding Ecology of Steller's Eider and Long-Tailed Ducks in Winter, Waterbirds: The International Journal of Waterbird Biology, Vol. 24, No. 3 (Dec., 2001), pp. 407-412
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Bustnes et al. (2001) studied this question.
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