Experimental novelty and tonic immobility in chickens (Gallus domesticus ).

The tonic immobility reactions of individually-caged adult hens were observed in familiar or novel environments when the experimenter wore either a familiar or unfamiliar coat. Birds tested in isolation in an unfamiliar environment showed longer tonic immobility than did those tested in their familiar environment where they could still see and hear their neighbours. Tonic immobility was significantly prolonged in both test environments if the experimenter wore an unfamiliar coat. The potentiation of tonic immobility by novel aspects of the experimenter's appearance may thus be superimposed upon that elicited by social isolation and novelty of the physical environment.