Dietary Variability in Redtail Monkeys (Cercopithecus ascanius schmidti) of Kibale National Park, Uganda: the Role of Time, Space, and Hybridization

© 2017, Springer Science+Business Media, LLC. Studies of the diet of different groups of the same species allow us to understand intraspecific dietary variability. I collected dietary data from six neighboring groups of redtail monkeys (Cercopithecus ascanius schmidti) and three hybrid monkeys over 12 years at Ngogo and from one group at Kanyawara in Kibale National Park, Uganda and compared these results with previous studies of redtail diets elsewhere in Kibale and from the Kakamega Forest of Kenya. I scored feeding as a particular monkey ingesting a species-specific plant part, or catching insects from a species-specific substrate. A new feeding score was tallied for the same combination of parameters only after a 30-min interval or if the identity of one of the three parameters changed. I counted trees along transects in the home ranges of the two main study groups to calculate food selection ratios. I used chi-square tests to compare diets between groups and time periods and Spearman rank correlation coefficient tests for dietary correlates. These comparisons reveal considerable variation in plant parts and species eaten by redtails between months, years, and neighboring groups with overlapping ranges. Selection ratios show that some tree species are important sources of plant food, while others are more important as sources of invertebrates. The high incidence of insectivory by redtails demonstrates another ecological role they play in addition to seed dispersal. The intrademic variation in diets I describe for Kibale was often as great as and sometimes greater than the interdemic variation. The diets of the hybrid monkeys at Ngogo differed in some ways from their parental species, particularly in their greater consumption of invertebrates. Introgression may have led to some of these differences within and between redtail demes. The pronounced variability in redtail diets demonstrates why a typological perspective of species is unwarranted and that the validity of interspecific comparisons requires a thorough understanding of intraspecific variation.