THE DIET OF DUCK AND COOT ON LAKE NAIVASHA

Abstract

Summary The diet of coot and duck on Lake Naivasha has been investigated to provide information on the duck/coot interaction. Some 79 duck and coot were shot in a limited area over a period of 24 h, and their stomach contents preserved in 4% formalin. The analysis of stomach contents was performed in two stages: large particles being completely identified and counted, small particles being sampled. The results of the analyses are considered to be most usefully expressed as proportions of food component by number of particles. Identification of components has been made by matching epidermal characters with collected plants, by matching shape and structures of seeds with collected seeds, and by recognition of such materials as arthropod exoskeletal fragments and molluscan shell. Some components have not been specifically identified. A discussion has been presented on the problem of relating the results of stomach‐content analysis to ecologically significant differences in feeding. The discussion hinges on four questions: Is the result of a stomach‐content analysis an accurate and appropriate indication of the stomach‐contents of a bird when shot, and, if so, do the results presented indicate differences between stomach contents? What is the relationship between stomach‐contents at the time of shooting and food ingested over the immediately preceding period, and do differences between stomach contents indicate differences in food intake? How far do differences in diet so deduced apply to the whole population of birds concerned in the study? Are the differences in diet relatable to availability of food, and can any valid inferences be made concerning the birds' interaction? It is concluded that at the time of the shooting, over the limited area examined, there was little overlap in diet for important components, and therefore probably little competition for food among the duck species and coot. Some general observations have been made on the feeding biology of duck and coot, and it is pointed out that the feeding apparatus of coot differs from that of all duck species in having shearing edges. This difference is related to the dietary differences in a predictable manner.