Changes in chicks' responses to novel moving objects over the sensitive period for imprinting

Abstract

The responses of isolated domestic chicks to a standard moving object on each of the first 5 days after hatching are described and the relations between some of the behavioural measures are analysed. Except on the first day after hatching when nearly all the chicks approached and nestled against the moving model, the majority of the chicks avoided for at least part of the test. The time spent avoiding in each minute steadily declined during the test and many chicks stopped avoiding altogether. The majority of the chicks which ceased to avoid the model then approached, nestled against it and subsequently followed. There was a strong positive correlation between the point at which avoidance ceased and the point at which positive responses were first given. After following had begun the time spent following in each minute tended to increase. The persistence of avoidance and the higher values of the strength of avoidance were negatively correlated with the strength of following. The positive correlation between the lower values of the strength of avoidance and the strength of following was attributed to their both being measures of locomotive ability. The proportion of birds which gave positive responses declined from the first to the second day and the proportion avoiding increased over the same period. The persistence of avoidance, the strength of avoidance, the latency of positive responses and the strength of following all increased up to the third or fourth day but thereafter declined. The increase in the strength of following is attributed to developing locomotive ability. The other initial changes are regarded as consequences of the process by which the isolated chicks learn the characteristics of the static environment in which they are reared. The negative relations between the measures of avoidance and the strength of following support the view that they are all measures of the birds' ability to discriminate between familiar and unfamiliar objects.