Primates spend the majority of their waking hours feeding, resting, and traveling between feeding sites. Their remaining time each day is devoted to what can be characterized as nonsubsistence behaviors, including affiliative, or friendly, social interactions, such as grooming and intergroup encounters. The proportion of the activity period (the period of time an animal or group of animals is active each day) devoted to each of these behaviors is reflected in what is referred to as an activity budget. The construction of activity budgets is fundamental to primate field research because the proportion of time spent by each animal in different activities can serve as a proxy for energy use (Halle and Stenseth 2000). For the individual, survival, growth, and reproduction are dependent on maintaining a balance between energy intake and energy expenditure (Pianka 1988). Thus differences in the average time budgets between populations, within populations over time, or between different age-sex classes may point to the presence of some form of ecological pressure (Dunbar 1992).