Defensive distance and immobility in young precocial birds (Gallus gallus).

The manifestation and duration of the tonic immobility reaction in 3-day-old chicks (Gallus gallus) was found to vary reliably as a function of the spatial proximity between the hand of the experimenter and the immobilized chick. The results of this experiment indicate that young birds are susceptible to immobility and that the maintenance of close spatial proximity is the condition necessary for the occurrence of the reaction in young precocial birds.