Bibliography: p. 105-117The Central American black howler (Alouatta pigra) occurs in surprisingly small social groups, for reasons that are not well understood. To test whether indirect withingroup feeding competition constrains group size, I examined the effects of group size on day journey length, activity budgets, and group spread; compared food availability and dietary quality with energy expenditure; and evaluated the results in light of influential ecological constraints models. 45 full day follows were completed on 3 groups of wild A. pigra varying in size from 3 to 7 individuals. Food availability for all groups was similar, but group size was not associated with increased activity levels or day journey length, nor did any group experience variation in energy expenditure with changes in food availability, indicating that feeding competition is not acting to constrain group size at this site. Consequently, I suggest that other factors (possibly social ones) are responsible for small group size
