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 female parental investment will be reflected in their behavior during intergroup encounters, the strategies actually pursued by adults of each sex during intergroup encounters remain poorly known for most primate species. Over an 11-month period, I examined the functions of adult male and female participation in intergroup aggression in five groups of eastern black-and-white colobus 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 are not uncommon. During 174 study days, I observed 136 encounters, most of which were aggressive in nature. I evaluated the hypotheses that through intergroup 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 defending food resources. I found strong evidence consistent with both the direct male mate defense and indirect male mate defense via resource defense hypotheses, but no evidence consistent with the male mate attraction via infanticide hypothesis. There was little evidence in favor of the female resource defense hypothesis beyond the fact that females occasionally participated 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 female resource defense appears to be most common in species with high levels of female philopatry. The indirect male mate defense via resource defense strategy has rarely been evaluated and may be a more common male strategy than is currently believed. I present a hypothesis that predicts when male primates are expected to defend resources for females in their group.