The effects of social experience and inductive procedure on tonic immobility in domestic chicks

Previous studies on tonic immobility in fowl have used a variety of inductive procedures and rearing conditions. The present study sought to parametrically evaluate the effects of three common methods of induction: ventral, dorsal and lateral placements within the context of groups of varying social composition: isolates, groups of three and groups of six, on the duration of tonic immobility. To that end 108 White Leghorn chicks were assigned to the nine experimental groups and tested once daily for the first fourteen days post-hatch.

Each of the three inductive procedures was found to differ significantly from each of the other two methods in the second week post hatch with dorsal placements producing the highest durations followed in effectiveness by the ventral and lateral methods respectively.

Previous findings that social experience is necessary for the appearance of robust immobility was confirmed, with the isolate reared chicks demonstrating significantly lower durations than the two social conditions.

No decline of the immobility response with repeated testing across days was found and two explanations for this were offered. Evidence supporting the concept of a maturational period was also noted and discussed.