Imprinting and the immobility reactions of domestic fowl

Abstract

1. 1. Chicks were reared socially or in isolation for 0, 1, 3 to 4, 8 or 14 to 16 days and then each chick was tested for the immobility reaction by holding it down on its back for 15 seconds in unfamiliar surroundings. Most of the chicks that remained immobile for 1 minute or for 5 minutes were socially reared chicks aged 8 and 14 to 16 days. The response was less prevalent in the latter age group and rare in the earlier age groups. 2. 2. Chicks were reared socially or in isolation for 8 or 14 to 16 days and then tested for the immobility reaction both alone and when close to a small group of chicks. The Social chicks tended not to show the immobility response when tested in the sight of other chicks. The Isolates were unaffected by the presence of chicks. 3. 3. Since Isolates tended not to show the immobility response at all and Socials tended to do so chiefly when tested alone it is suggested that this fear reaction is largely due to the separation of the chick from its companions. The importance of the visual stimulation from the moving and animate environment is indicated and the results discussed in terms of the relationship between imprinting and fear. 4. 4. The delay of 7 or 8 days in the appearance of the immobility reaction is considered in relation to possible physiological maturation of the immobility response itself or of fearfulness. Explanations of the maturation of fearfulness are considered in terms of the effects of social experience on the development of adrenal secretion and on the establishment of a familiar social environment. This latter possibility is in accordance with the view that the process of imprinting establishes the familiar social environment and that fear responses, including the immobility response, are evoked by drastic changes in this environment.