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A comparison of data on ranging, activity budgets and frequencies of social behaviour gathered over a range of group sizes for an omnivorous, forest-living monkey, the long-tailed macaque (Macaca fascicularis), showed that the length of the day journey, the time spent travelling and searching for dispersed food items, as well as social tension, show a monotonic increase with group size. A behavioural mechanism behind these patterns is the “puhing forward” effect: foraging animals tend to move away when approached by others, presumably because they reduce the availability of dispersed food items in patches they have searched. By avoiding being overtaken animals are not forced to search in depleted patches. An alternative mechanism, the limited capacity of fruit trees, does not operate in the present case. It is concluded that theories postulating feeding advantages to be the primary factor favouring …