Group Behavior of Rhesus Macaques in the Second Year of Their Lifespan

We analyzed the behavior of nine unrelated rhesus macaques(Macaca mulatta) aged 14–18 months, takenfrom different family groups and placed into a new habitat context.We carried out daily two-hour observations of the newly formed groupover two months to assess the dynamics of exploring the space of anew enclosure by the monkeys and to analyze the aggressive, friendly,and orienting-exploratory behaviors of the individuals with regardto their age and sex. The macaques explored a new enclosure space(1) top-down, (2) from periphery to center, and (3) from stationaryto mobile (enrichment) elements. The behavioral analysis revealedthe interaction between the age and sex factors. The older individualsof both sexes were more aggressive than the younger, apparentlysuggesting the dependence of the emerging social status on the ageof individuals. Age-related differences in the manifestation of friendlinesswere only observed among females: the older individuals were morefriendly than the younger. At the same time, males were more aggressivethan females among the older macaques, while being more friendlycompared to females among the younger individuals. Females showeda more pronounced orienting-exploratory behavior compared to malesamong the younger macaques, although there were no sex differencesamong the older individuals. In general, all three types of behavioral activitywere equally represented in the older males; friendliness and exploratoryreactions dominated in the younger males and older females; andexploratory behavior dominated in the younger females. We hypothesizedthat in the postnatal ontogenesis of macaques, 14–18 months is acritical period, when their higher nervous activity undergoes maturation.These results can be instrumental in creating a biological modelof in-group behavior, aimed at improving the care of macaques inlaboratory conditions.