Effects of Pairing of Chicks During the Imprinting Period on Filial Responses to an Imprinting Stimulus

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There are several studies which have evaluated the effects of social contact with siblings on imprinting to a maternal surrogate. However, we have no consistent effect of the social experience. Some studies have reported that social experience with siblings interferes with the establishment of imprinting, whereas other studies have reported that social experience with siblings enhances the imprinting experience.The present study examined the effects of social contact with one sibling during the imprinting sessions on imprinting to the maternal object for chicks (White Leghorn). This experimental situation is similar to the natural setting because under natural conditions imprinting occurs in a social situation which includes a parent and siblings. Next, this study investigated the interrelation between each chick's responses to its partner and those to the imprinting object.During the imprinting sessions, each chick was individually exposed to only the imprinting object under the isolated condition or exposed to both the stimulus and one sibling under the paired condition over three days after hatching. Each chick showed the better performance under the isolated condition than under the paired condition. Thus the presence of one sibling during the imprinting period weakens the strength of the imprinting.The more interesting result was that chicks who had showed a poor performance under the first paired sessions followed the stimulus well under the later isolated condition. It seems that these subjects have already fully imprinted to the stimulus in spite of poor experience of following the stimulus. This result renders dubious the significance of following as an index of the strength of imprinting.Next, it was often observed under paired conditions that as soon as a well-imprinted chick followed the stimulus, the other chick ran behind him quickly. It was also observed that this well-imprinted chick followed its partner and pecked at him frequently. We can consider there is some interrelation between social responses to a sibling and those to a surrogate mother.