Group Fission in Red-tailed Monkeys (Cercopithecus ascanius) in Kibale National Park, Uganda

Abstract

We describe group fission in Schmidt’s red-tailed monkeys (Cercopithecus ascanius schmidti) at the Ngogo study site, Kibale National Park, Uganda. The process of group fission lasted several months, beginning when the original group (Ss) reached just over 50 individuals. For both daughter groups, rates of both intragroup and intergroup aggression increased following fission. Rates of intergroup aggression were especially high immediately following fission as the two daughter groups fought frequently while establishing a new territorial border. The larger daughter group continued to use the original home range of Ss whereas the smaller daughter group shifted its home range. The displaced daughter group increased daily travel distances following group fission as they established a new territory, and no infants were born the year after fission. The members of Ss were last involved in a group fission 18 years ago, suggesting a faster rate of group fission compared to population-level estimates (one per 35 group-years). The especially high frequency of group fission relative to the rest of the population is deserving of further study.