During two years from 1976 to 1978, 11 instances of the broodinesses of domestic ducks were observed in the open yard feeding. In two cases the broodinesses reached successfully the hatching and rearing. Female ducks laid sporadically at first, but thereafter the egg-laying places became limited to one particular point in the shed. Down feather plucking and nest-material throwing (sideways building) were seen as the nest building behaviour. The so-called nest down, which was darker than the

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... nary down, grew during the nest building and incubation period. Female ducks plucked nest downs and used them as nest materials. The nest material carring behaviour was observed as the variation pattern derived from the sideways building that was primarily the nest building behaviour itself. It is considered that the nest-material carring behaviour in the duck is at the primitive stage in the evolution of this behaviour pattern. Nests were built up of straws and nest downs by the sideways building. The male duck did not participate in the nest building during our observations. (Japan. Poult. Sci., 18, 313-318, 1981)