When are there Influxes in Blue Monkey Groups?

Summary

Cercopithecus mitis groups show variation in male number during the breeding season. The 23 years of male residence records from multiple groups of blue monkeys in the Kakamega Forest reveal that influxes occurred in 23% of breeding seasons, and coincide with greater number of sexually active females in the group on both per-season and per-day bases. In six of ten seasons with sufficiently detailed records, female sexual behavior preceded the arrival of multiple males in the group, while in one year, male visits came first, and in the remaining three years, estrus and the presence of more than one male occurred essentially simultaneously. It is likely that estrous females bring males to the group, but also that the presence of males feeds back positively on estrus behavior in females. The number of males in the local area, or intruder pressure, may also explain some variation in male numbers. These data, which are the most extensive for any guenon population, are generally supported by other investigations of different populations and species. The number of sexually active females, as well as intruder pressure, are two important components of female defendability that influence the number of males present in the breeding season in at least three guenon species.