AbstractIn the Amazon Basin of northeastern Peru, moustached (Saguinus mystax) and saddle-back (S. fuscicollis) tamarins form stable mixed species assemblages in which groups of each species feed, forage, rest, travel and cooperatively defend a territory throughout the entire year. Data presented indicate that despite extreme overlap in feeding and ranging behavior, a change in troop size did not have a significant affect on dietary preferences, activity budgets, day range, foraging effort, and the number and length of daily feeding bouts of either resident species. The larger troop, however, was more successful at defending major feeding trees than the smaller troop. Unsuccessful resource defense resulted in a decrease in time spent feeding and foraging, and an increase in the distance traveled to the next major feeding site. It is proposed that within-troop feeding competition is generally not a critical factor in the feeding ecology of this mixed species tamarin troop. Rather, the formation of such a troop enables each resident species to more effectively exploit and defend a set of productive feeding trees.
