Niche expansion of a cryptic primate, Callimico goeldii, while in mixed species troops.

We examined the effects of polyspecific associations on the behavior of one group of Callimico goeldii in northwestern Bolivia. Data were collected for 1 year using focal animal sampling at 5-min intervals, for a total of 1,375 observation hours. In total, C. goeldii formed mixed species troops with five groups of Saguinus fuscicollis and six groups of S. labiatus, and these were maintained during 81% of observations. C. goeldii rested more and traveled less while alone than while associated, but neither vigilance behavior in the understory nor habitat use were affected by association status. The composition of the group's diet was different while alone (higher in structural carbohydrates [fungi] and lower in simple sugars [ripe fruits] and protein [insects]) than while associated (fungi 65 vs. 37%; fruits 13 vs. 32%; insects 5 vs. 15%). We propose therefore, that C. goeldii has a lower quality and more narrowly based diet while alone as compared to while associated. The factors that allow for this dietary expansion while in mixed species troops require further investigation.