Data on fruit feeding rates and daily path length were compared for four groups of woolly monkeys in Tinigua National Park, Colombia. Indirect evidence was found for feeding competition both within and between groups. Feeding rates were similar across groups of different sizes, but daily path lengths were longer in small and large groups when compared to medium-sized groups. The results suggest that the optimal group size in this study site is close to 20 individuals. Although the sample size was small and it was difficult to assess the influence of home range quality in some of the comparisons, this is one of the few studies providing empirical evidence supporting the importance of intergroup competition affecting group size in primates.