The Interaction of Experience, Stimulus Characteristics and Exogenous Androgen in the Behaviour of Domestic Chicks
Authors: Salzen Eric A. 
Published: April 2008

AbstractThree experiments studied the behaviour of normal domestic chicks and ones that received a single injection (50 mgs) of a depot preparation of testosterone oenanthate at 2-3 days posthatch. In Expt 1 solitary reared hormone treated (6) and control (6) chicks had no experience of moving objects. In Expt 2 similar solitary reared chicks (6 hormone and 6 control) each had continuous visual experience of a neighbouring chick. In Expt 3 solitary reared hormone (4) and control (4) chicks and socially reared hormone (9) and control (9) chicks had 2 mins experience every other day of a hand placed in the cage. All were tested at various times from 7 to 25 days for their responses to a hand, a dead chick and a live chick of their own kind placed in their cages. The behaviour observed was classified into Fear, Exploration, Sex, Aggression, and Indifference and the behaviour patterns in each category have been described. When confronted with a prone hand Fear was least in Expt 3. When confronted with a dead chick or a live chick similar to themselves Fear was least in Expt 2. Where Fear was least, hormone treated groups showed most Sex and Aggression and control groups showed most Exploration and Aggression. Thus the occurrence of Fear seemed to depend on the absence of previous experience of the test object. Furthermore, where Fear was absent Sex, Aggression or Exploration seemed to be evoked according to the appropriateness of the stimulus and of course the androgen level in the chick. The prone hand and the dead chick elicited Sex in the hormone chicks and Aggression or Exploration in the controls. The results with the live chicks seemed to depend largely on the kind of chicks involved. Encounters between solitary hormone chicks produced intense Sex and Aggression; those between solitary controls produced some Aggression and Exploration; while those between solitary hormone and control chicks resulted largely in Indifference. Other encounters were arranged between all the different types of chick. The results considered with those for the intensively studied solitary chick encounters suggest that solitary hormone chicks stimulated each other to Sex and Aggression and reacted to all other chicks with Fear or Indifference, that solitary and socially reared control chicks reacted in all encounters with Fear or Indifference with some Exploration and Aggression and that socially reared hormone treated chicks showed Sex and Aggression with all types of chick, except solitary hormone chicks with whom they showed Indifference, but only when tested separately and not when tested in their social groups where Indifference with some Exploration prevailed. The results suggest that unfamiliar objects evoke fear behavior which masks sexual and social behaviour. When fear is absent sexual or social behaviour will be elicited according to the hormone condition of the chick and depending on the object providing appropriate stimulation. Such stimulation may involve few and non-specific sign stimuli since the hand and the dead chick as well as a live chick could elicit sexual and aggressive behaviour. Social chicks were much less liable to respond at least when in the group and this could be due to factors such as stimulus satiation and social inertia or learned inhibitions and adjustments. Aggressive behaviour seemed to be elicited simply by rapid movements and tall or erect objects or postures and was shown by all solitary chicks in Expt 3 towards an erect hand with fingertips at the top. Again, and possibly for the same reasons the social chicks were much less responsive. An attempt was made to explain all the data in terms of the interaction of a) avoidance of hitherto unseen objects in the manner predicted by a neuronal model hypothesis of imprinting, b) the appropriateness of the stimulus object for eliciting innate response patterns, c) stimulus satiation effects and d) social inertia. The possibility that an interaction of such factors could account for the phenomena of imprinting and its effects on later sexual and social behaviour has been discussed.