The effects of seasonality on ranging behaviour and diet
In large tropical rainforests, switching to fallback foods may be relatively easy for red-tail monkeys. These expansive forests generally contain a greater diversity of plant species and are more structurally complex than savanna environments. Even if high density food patches produce little fruit, the cost of travel from one patch to another may be high. Conversely, savanna environments present a novel challenge to red-tail monkey foraging strategies. Food is widely distributed and there may be fewer overall foods available during certain times of year. To better understand how these forest guenons adapt their feeding strategies to seasonal changes in resources, then, the purpose of this study is to examine (a) what constitutes preferred and fallback foods for C. ascanius in a mosaic environment; (b) how ranging patterns of C. ascanius change in response to dietary shifts; (c) how group size and social structure change with fluctuations in food availability and; (d) the effects of frugivorous competitors on foraging behaviour in red-tail monkeys.
Recently, we have begun to identify and monitor the behaviour of multiple resident males in our focal troop. Like chimpanzees, red-tail monkeys live a population densities a fraction of what they do in tropical forests, and it may be that the costs to dispersal are high enough to prevent typical migration patterns. Below are some photographs by E. Mclester of some of the resident males and a video by C. Vitet, who investigated male-male tenure and rank at Issa over a four-year period. The figure is from her thesis, and describes the fluctuating number of males in the group over a four-year period: