Individual or paired exposure of domestic chicks to an open field: Some behavioural and adrenocortical consequences.

The interpretation of open-field behaviour in chickens is unclear because conflicting effects of manipulating the social environment during testing have been reported. The behavioural and adrenocortical responses of chicks exposed individually or in pairs to an open field were, therefore, examined in the present study. Chicks tested individually showed significantly higher levels of activity, vocalization, defaecation and plasma corticosterone but took longer to ambulate and preened and pecked at the environment significantly less than their paired counterparts. There were no differences between treatment groups in either the durations of freezing or the latencies to vocalize. Social motivation is thought to be an important variable influencing the chicks' strategy but the present findings are wholly consistent with an interpretation of chicks' open-field responses based on the fear hypothesis.