Altruism Among Female Macaca Radiata: Explanations and Analysis of Patterns of Grooming and Coalition Formation

Analysis of the observed patterns of two forms of putative altruism (grooming and coalition formation) among adult female members of a group of captive bonnet macaques (Macaca radiata) indicates that both kinship and dominance rank influence the distribution and rate of these behaviors. Females groom their adult relatives more often and more reciprocally than they groom unrelated females of similar ranks. In addition, females are more likely to support their relatives than nonrelatives and are likely to incur greater risks when they do so. Grooming and coalition formation do not occur exclusively among kin. Females primarily groom higher ranking females and support unrelated females against females lower ranking than themselves. Although females do not preferentially support unrelated females that groom or support them most, they do refrain from harassing lower ranking females that are currently grooming them or a female higher ranking than themselves. Thus, by grooming a higher ranking female a female reduces the probability that she will be harassed by other females. The relationship of these results to predictions derived from several different sociobiological hypotheses is discussed.