Abstract
1. Previous work has shown that there are sex differences in the open‐field behaviour of 7‐d‐old domestic chicks. General activity is higher in females, whereas males respond by sitting or lying. It could be argued that such findings merely reflect the fact that females are generally more active than males. In the present study, therefore, a number of behaviour patterns were recorded both in the chicks’ home cages and in an open field or novel environment. 2. Differences in behaviour between the two sexes were found in the open field as before but not in the home cage. 3. This suggests that there is a genuine dichotomy between males and females in their responses to a novel environment. 4. The quantitative changes in behaviour patterns seen when chicks are moved from their home cage environment to a strange open field are consistent with the hypothesis that a novel environment evokes fear, especially in males.