Quantitative Observation of Behavior in Free-Ranging Macaca Mulatta: Methodology and Aggression

Abstract

AbstractQuantitative methods of data collection and analysis were used to assess patterns of aggressive interaction in rhesus macaques. Four social bands were observed for 488 hours over a twelve-month period using standardized observation techniques and behaviors and recording data on monkeys in both feeding and non-feeding contexts. The numbers of monkeys present within the prescribed observation areas, the frequencies of three aggressive behaviors and the occurrence of open wounds were recorded for three age-sex classes; adult males, adult females and juveniles. The data revealed that more monkeys were present in the observation areas during the mating season, that levels of aggression varied inversely with group size, smaller groups exhibited higher levels of aggression and that male and female aggression was higher during the mating season, while juvenile agonistic interactions reached a peak during the weaning and birth periods. There were 46% more aggressive acts in the feeding than in the non-feeding context but the seasonal and group patterns were nearly identical between the two contexts. Arguments were presented supporting the use of the interactions/hour/ possible interacting combination of monkeys as a dependent variable; the data from this study and comparisons with other reports indicate that this is a logical variable to use. Lastly, several methodological tests demonstrated that there are potential biases in the use of the traditional field-note method of data collection; only a small percentage of the total behavioral interactions are recorded with the field-note technique and there is a tendency to record a disproportionately greater number of interactions initiated by larger adult monkeys. These disadvantages of the field-note method must be weighed against the need for individual identification.