Male and female strategies during intergroup encounters in guerezas (Colobus guereza): evidence for resource defense mediated through males and a comparison with other primates

Although socioecological theory predicts that differences in male and femal e parental investment will be reflected in their behavior during intergroup encounters, the strategies actually pursued by adults of each sex during i ntergroup encounters remain poorly known for most primate species. Over an 11-month period, I examined the functions of adult male and female particip ation in intergroup aggression in five groups of eastern black-and-white co lobus monkeys, or guerezas (Colobus guereza), in the Kakamega Forest, Kenya . Guerezas are large-bodied arboreal African colobine monkeys that usually live in one-male multifemale groups, though multimale multifemale groups ar e not uncommon. During 174 study days, I observed 136 encounters, most of w hich were aggressive in nature. I evaluated the hypotheses that through int ergroup aggression (1) males were directly defending mates, (2) males were indirectly defending mates by directly defending food resources, (3) males were attempting to attract mates via infanticide, and/or (4) females were d efending food resources. I found strong evidence consistent with both the d irect male mate defense and indirect male mate defense via resource defense hypotheses, but no evidence consistent with the male mate attraction via i nfanticide hypothesis. There was little evidence in favor of the female res ource defense hypothesis beyond the fact that females occasionally particip ated in intergroup aggression in four of the five study groups. A review of the most intensive studies of primate intergroup encounters suggests that direct male mate defense may occur in almost all primate species, while fem ale resource defense appears to be most common in species with high levels of female philopatry. The indirect male mate defense via resource defense s trategy has rarely been evaluated and may be a more common male strategy th an is currently believed. I present a hypothesis that predicts when male pr imates are expected to defend resources for females in their group.