Early development of peer dominance relationships in a captive group of Japanese macaques Macaca fuscata

We studied early development of peer dominance relationships in a captive group of Japanese macaques Macaca fuscatafuscata at the Primate Research Institute of Kyotu University. This study aims to give detailed descriptions on characteristic patterns of maternal rank acquisition from infant to juvenile. Focal subjects were 22 young monkeys belonging to three cohorts born in 2002, 2003 and 2005. Data were collected with a total 2130 sessions of 30-minute continuous recording of focal subjects combined with all occurrence-sampling methods. The onset of aggressive behavior varied per cohort and was delayed in cohorts with fewer close-aged associates. More than 60% of dyadic combinations in agonistic interactions between peers were unidirectional throughout the study period. Although some bidirectional interactions could have involved unstable relationships between particular individuals, most of the bidirectional interactions included a few continuous series of alternating one-sided interactions.A linear order could be found among peers from the first appearance of aggressive behavior, and nearly 90% of those dyads were concordant with that of their mother's rank order. Young males were responsible for most of the dominance relations that would not be predicted based on their mother's rank. These results suggest that infant monkeys may recognize their own social status relative to their opponent's before onset of aggressive behavior and adjust themselves into the matrilineal rank system accordingly.