Abstract
Social factors involved in the control of impulsiveness were examined in domestic chicks. In binary choices between a large/long-delay option (LL) and a small/short-delay alternative (SS), chicks that had been competitively trained in groups of three individuals showed fewer choices of LL than did those trained in isolation (experiment 1), suggesting that competition causes impulsive choice. In experiment 2, in order to identify the critical factor involved, we tested the effects of perceived competition (coincident feeding without interruption) and scrounging (gaining food without pecking bead) separately. To examine the effects of risk/noise that individual chicks experienced in competition, the food amount varied randomly in trials according to a binomial distribution around the expected mean. Perceived competition primarily contributed to the influence on the impulsive choice, whereas the contribution of scrounging was weaker. Collection risk did not explain the social influences since the perceived competition was not accompanied by actual interruption of the delayed food reward. The risk owing to variable food per se did not cause impulsive choices. Coincident foraging during competition is thought to play a critical role.