Introduction

Primatologists have only recently begun to investigate the impact of predation on foraging strategies, and the many variables that might mediate this relationship. Traditionally, success in foraging and success in avoiding predators were treated as two independent phenomena. Both might depend upon group size, but the interaction was rarely considered (e.g., for capuchins, Miller 1992, de Ruiter 1986, Srikosamatara 1987). This study explores the extent to which group size influences perceived risk of predation and how this, in turn, affects food intake. Data come from an ongoing study of one population of wedge-capped capuchins (Cebus olivaceus), living at the Hato Piñero Biological Reserve in central Venezuela.

Previous studies with this population of capuchins revealed a strong link between group size and seasonality in food intake. Adult females living in larger groups maintain an essentially constant level of food intake throughout the year (approximately 1800 cm3 of food per female per day, on average). In contrast, those in smaller groups experience dramatic annual variation, consuming very little during the dry season (approx. 1100 cm3) but much more in the wet season (approx. 2900 cm3) (Miller 1996). This pattern is only partly the result of differences in foraging effort. During the wet season, small-group females devote significantly more time to feeding and foraging than do large-group females (68% and 55%, respectively, of their daily activity budgets) and so the disparity in food intake is predictable. However, during the dry season, foraging time is not significantly different (58% in larger groups and 54% in smaller groups) (Miller 1996).