Variation in digestive organ size among five species of diving ducks (Aythya spp.)

Abstract

Ceca length, small intestine length, and gizzard weight were measured for individuals of five species of diving ducks collected at Long Point Bay, Lake Erie, and Mitchell's Bay, Lake St. Clair, Ontario, in the falls of 1982 and 1983. The five species were Lesser Scaup (Aythya affinis, N = 84), Ring-necked Duck (Aythya collaris, N = 57), Greater Scaup (Aythya marila, N = 54), Redhead (Aythya americana, N = 58), and Canvasback (Aythya valisineria, N = 112). The diets of these species reportedly differ in diversity as well as in amount of fibre, and interspecific differences in gut morphology, not explained by differences in body weight, were accounted for by general differences in diet. Canvasbacks, although the heaviest species, had the shortest ceca, short intestines and light gizzards, presumably because their diet contains the least fibre. Conversely, the relatively small-bodied scaup species had the longest small intestines, likely because of their diverse diets which include animal and plant material. Our results show that morphological differences in waterfowl guts reflect dietary differences at a particular time and location and also illustrate the importance of adjusting gut measurements to body weight before making interspecific comparisons.