A comparison of interspecific differences in the morphology of external and internal feeding apparatus among North American Anatidae

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Abstract
We examined the relationship among bill shapes and gut morphology for 22 species of North American Anatidae. Bill shape was defined by nine bill measurements. Gut morphology was defined by the wet weights of empty ceca, small intestine, and gizzard. Interspecific differences in morphology were quantified through a canonical discriminant function analysis. Although the pattern of interspecific differences in the two sets of measurements showed some similarity (P < 0.001) this relationship was weak (R2 = 0.057). Species that were very similar or different in bill shape tended to be very similar or different in gut morphology. At any given intermediate distance of separation in either bill shape or gut morphology there was a wide range in separation in the other axis. We conclude that interspecific differences in both bill shape and gut morphology should be considered in studies of resource partitioning between closely related species at a particular time and location.