The development of responses to novel-coloured objects in male and female domestic chicks.

Male and female domestic chicks were trained to peck on a small coloured (red or green) box for food reinforcement. They were then presented with one box identical to that used during training (familiar) and one of a different colour (unfamiliar) and their preferences were assessed in a simultaneous free choice test. The novel colour was green in chicks trained with a red box and red in chicks trained with a green box. Chicks showed marked variations in their preferences for familiarity and novelty as a function of age and sex. In chicks trained with a green box preferences for the familiar colour were stronger in females than in males at all ages of test. A similar sex difference was observed in chicks trained with a red box, except that at around day 9, when males showed temporarily stronger preferences for familiarity than females. When comparing males and females of red-trained chicks to those of green-trained chicks, a shift in colour prefernce, from red to green, was apparent from day 9 in both sexes, though temporarily stronger in females than in males. Levels of preference for the familiar object showed a peak (centred at around day 5/6) and two dips (centred at around day 4/5 and day 10/11) in both sexes irrespective of colour. Results are discussed in relation to current evidence for simultaneous changes in the brain and in the behaviour of young chicks during development.