The importance of being first:A primacy effect in filial imprinting

The stability of filial preferences of domestic chicks, Gallus gallus domesticus, was investigated. In a series of experiments, preferences were measured in simultaneous choice tests at the end of 3-day periods of exposure to conspicuous artificial objects. In experiments 1 and 2, day-old chicks were exposed to one of two coloured cylinders, followed by exposure to the alternative stimulus. The original preference was significantly reversed. After a third phase of the experiment, during which the chicks were isolated (experiment 1) or exposed to the two stimuli simultaneously (experiment 2), the preference changed significantly towards the first object. A significant preference for the first object was reacquired in only one combination of stimuli in experiment 2a. The results were similar for experiments 2b–2d, in which the period of exposure to the first (2b) and the second (2d) object was increased or when there was a period of isolation after exposure to the first object (2c). In all these experiments, the stimuli differeed only in the single dimension of colour. In experiment 3, the two stimuli used differed in colour, shape and pattern. Three days of exposure to one object, followed by 3 days exposure to the other object and 3 days to both objects simultaneously, led to a significant ‘resurfacing’ of a preference for the first stimulus, irrespective of which stimulus was presented first. These results confirm that the reversal of filial preferences need not be permanent and are consistent with, a ‘competitive exclusion’ model of imprinting