Conspecific vocalisations, tonic immobility and fearfulness in the domestic fowl.

Vocalisation is important in the transmission of fear/alarm among chickens. In this experiment, therefore, the effects of various conspecific calls on tonic immobility, a fear-potentiated, anti-predator response, were examined in adult laying hens. The shortest durations of immobility were observed after exposure to recordings of either the familiar background noise of the poultry house of 'Ku' calls which are normally associated with feeding. These stimuli exerted similar effects and both are considered more likely to attenuate rather than heighten fearfulness. Intermediate levels of immobility followed presentation of the post-laying cackle whereas recordings of warning calls, such as the aerial predator call, the ground predator call or the fear squawk, all significantly prolonged tonic immobility. The biological significance of these results is discussed in terms of fear and predator-defence.