Effects of prenatal exposure to corticosterone on filial imprinting in the domestic chick, Gallus gallus domesticus

The young of precocial species such as the domestic chicken can, shortly after hatching, imprint on a visually conspicuous object. The chicks' filial behaviour is influenced by a predisposition, directing its attention towards conspecifics, and a learning process, allowing it to distinguish between individuals. The concentrations of maternally derived steroid hormones found in birds' eggs depend on environmental factors and may be how the hen influences her progeny's behavioural development. We tested the hypothesis that prenatal exposure to corticosterone affects filial behaviour in the chick. Eggs in the treatment group were injected with corticosterone before incubation; eggs in the control treatment were vehicle-injected. In experiment 1, coloured chicks were used as imprinting stimuli and subjects were tested in a simultaneous discrimination test. Control chicks showed a significant preference for the imprinting stimulus, but treatment chicks did not. There was no difference between groups in preference scores, which measured memory of the imprinting stimulus. However, colour affected preference score differently between groups. Treatment chicks spent more time with stimulus chicks, regardless of colour, than did control chicks, indicating that corticosterone increased the strength of the predisposition. In experiment 2, chicks were imprinted on objects and tested in a sequential discrimination test. The results indicated a tendency for discrimination in the control group but no discrimination in the treatment group. No difference in preference score between control and treatment chicks was found.