Retention of individual recognition in chicks and the effects of social experience

Young domestic fowl chicks, Gallus gallus domesticus, discriminate between familiar and unfamiliar agemates. We investigated the retention of individual discrimination and the effects of social experience on such recognition memory. In the first series of experiments, chicks were paired with an initial social partner (I) for 22.5 or 42 h. These I pairs were then separated and each chick was housed with a new partner (Recent: R) for about 19 h. During subsequent tests, interactions between I partners did not differ from those of unfamiliar test pairs. However, chicks in R pairs pecked at their partners less frequently during the test trials and spent more time in physical contact than did unfamiliar pairs. Chicks in two additional experiments were similarly housed in pairs with an initial partner, then either isolated or housed with a new partner in an unlit room. After these treatment procedures, chicks in both experiments pecked at lower frequencies when tested with their I partner compared to an unfamiliar agemate. We conclude that retention of a memory trace of a social partner depends upon the chicks' intervening experience during the separation period. Exposure to a second individual interferes with the recognition memory of the first partner. Furthermore, the negative effect of the second partner on the retention of a memory trace of a previous partner depends on familiarization with the second partner's visual phenotype.