Interspecific differences in bill and tongue morphology among diving ducks (Aythya spp., Oxyura jamaicensis)

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Abstract
Twelve morphological characters of the bill and tongue were measured in six species of diving ducks (Aythya and Oxyura spp.). We used multivariate analyses to describe interspecific differences in morphology and related these differences to published information about food habits and feeding behavior of the six species. Canvasbacks (Aythya valisineria) have long, narrow, deep bills that are well suited to probing and grasping plant tubers from the substrate. Greater (A. marila) and Lesser Scaup (A. affinis) and Ruddy Ducks (Oxyura jamaicensis) have short, wide, shallow bills suited to straining food items. Lesser Scaup and Ruddy Ducks have the greatest lamellar density and this enables them to strain very small plant and animal material. Redheads (A. americana) and Ring-necked Ducks (A. collaris) have bills of intermediate size and shape that are suited to straining seeds and grazing leafy parts of plants. Lesser ang Greater Scuap, on the basis of bill morphology, are more similar to Ruddy Ducks than they are to other Aythya species. Overall, bill size and shape were more important in distinguishing the six species than were lamellar density or tongue characteristics.