Interspecific relations in a mixed-species troop of moustached tamarins, Saguinus mystax, and saddle-back tamarins, Saguinus fuscicollis (Platyrrhini:Callitrichidae), at the Río Blanco, Peruvian Amazonia.

This study examined the social interactions between moustached tamarins, Saguinus mystax, and saddle-back tamarins, Saguinus fuscicollis, living in a mixed-species troop at the Río Blanco, Peruvian Amazonia, between July 1985 and July 1986. Mixed-species troops were common among the S. mystax and S. fuscicollis populations in the Río Blanco study area; 72% of all sightings of S. mystax and 82% of all sightings of S. fuscicollis were in mixed-speices troops (study group excluded from analysis). In the study group, the two species spent on average 82% of time in association. Interactions were observed at a rate of one per 5 h of observation. Most interactions (96%) were agonistic. About 70% of agonistic interactions occurred at small food resources (crown diameter < 5 m and/or limited number of ripe fruits). Moustached tamarins were always dominant over saddle-back tamarins. Friendly interactions were extremely rare and were restricted to play invitations. Mutual calling was observed in the morning before the two species joined each other and during the day when they became separated. It is concluded that interspecific interactions and mutual calling incur some costs to the associated species but that these costs may be low.