Social Tension in Familiar and Unfamiliar Pairs of Long-Tailed Macaques

Abstract

The behavioural responses of monkeys to the pairing with familiar and unfamiliar individuals were analysed in order to test whether differences in social tension were related to different patterns of affiliation. Social tension was derived from the frequency of displacement activities. Ten familiar pairs (the F group) and 20 unfamiliar pairs (the UF group) of adult female long-tailed macaques (Macaca fascicularis) were observed in a two-hour test. The UF group was divided into two subgroups on the basis of the establishment of clearcut dominance relations within the pairs (as revealed by bared-teeth displays). Unfamiliar pairs showing clearcut dominance relations (the UFa subgroup) did not differ from the F group in terms of grooming exchanged and displacement activities. Unfamiliar pairs without clearcut dominance relations (the UFb subgroup) showed less grooming and more displacement activities. A delay in the onset of allogrooming due to unresolved dominance relations was responsible for the differences in social tension between the different monkey pairs. The results of this study suggest that unfamiliarity between the monkeys is not a good predictor of social tension if the patterns of behavioural interactions between the individuals are not taken into account.