Diets and Morphology of Digestive Organs of Five Species of Sea Ducks Wintering in Newfoundland.

Abstract

Gizzard weight, small intestine length, and caeca length were measured from specimens of sea ducks collected in coastal Newfoundland during the November to March winter seasons of 1982-88. The diets of Common Eiders (Somateria mollissima) (n=24), King Eiders (S. spectabilis) (n=25), Black Scoters (Melanitta nigra) (n=17), Old-squaws (Clangula hyemalis) (n=20), and Harlequin Ducks (Histrionicus histrionicus) (n=27) were entirely animal matter but differed in diversity and shell component. Common Eiders, King Eiders, and Black Scoters consumed a high proportion of mollusks and sea urchins, whereas, Oldsquaws and Harlequin Ducks consumed relatively high proportions of isopods and amphipods, respectively. Interspecific differences in morphology of digestive organs, not explained by body size, were accounted for by these general differences in diet. The largest gizzards were found in scoters and Common Eiders that had the highest shell component in their diets. The shortest digestive tracts were found in Black Scoters which had the most 'specialized' diet, although there was no significant difference between Black Sco-ters and Harlequin Ducks. Caeca length was similar between species, except they were exceptionally short in the Black Scoter. We were unable to speculate a functional relationship of the caeca, although it may be correlated to the diversity of the diet. These results confirm other findings that morphological differences in digestive organs in water-fowl reflect dietary differences.