Spatial and temporal determinants of samango monkey (Cercopithecus mitis erythrarchus) resource acquisition and predation avoidance behaviour

Abstract

Food acquisition and predator avoidance are principal components of the survival strategies of all primates. However, for primates, maximising food acquisition whilst minimising predation risk is often impossible. This leads to the existence of the foraging/risk trade-off, a mechanism fundamental in shaping life histories, species interactions and ultimately community assemblage. The principal aim of this study was to investigate how samango monkeys (Cercopithecus mitis erythrarchus) strategically balance the foraging/risk trade-off when exposed to spatially and temporally varying resources and risk.

Data were collected on a habituated group of samango monkeys over a 12 months observational period at the Lajuma Environmental Research Centre, South Africa. The focal group are part of a population near the southerly limit of the most southerly ranging African, primarily arboreal, monkey species. A biogeographical approach was also used, utilising ecological data from 12 different populations of C. mitis from a number of field sites across the species’ distribution.

Cold, dry winter periods were associated with increased time spent feeding and decreased in time spent resting. During winter months the samangos supplement their diet with foliar material, most likely due to the increased energetic requirements of maintaining body temperature. On a geographical scale, southern populations of samango have significantly more fruit in their diet than their more equatorial relations; whilst the opposite pattern is apparent involving the amount of animal matter consumed. On a spatial scale resources appear to be less important in determining samango ranging behaviour than the risk of predation. The study group actively avoid areas of perceived eagle predation risk, even though resources, such as food, are available in those areas. Similarly, the samangos increase time spent vigilant when in areas of high perceived eagle predation risk, but environmental factors such as visibility or food availability have little effect on vigilance.

The findings of this study indicate that a population at the edge of their species’ ecological tolerance are forced to considerably adapt behaviourally to seasonally and spatially varying resources and risk. In particular, great effort is put into avoiding predation risk; by avoiding high risk areas and maintaining an adequate level of vigilance. All of this must be achieved whilst combating rival groups and maintaining a territory, ensuring adequate food can be foraged and ensuring the successful raising of the next generation.