Activity Patterns, Intergroup Encounters, and Male Affiliation in Free-Ranging Bearded Sakis (Chiropotes sagulatus)

The assessment of how primates divide their daily activities is one of the foundations of primate behavioral ecology but the activity patterns and social behavior of the Pitheciines, including bearded sakis (genus Chiropotes), are poorly understood. During a 15-mo study, I collected 560 h of data on subgrouping, activity patterns, social behavior, and intergroup encounters of a group of free-ranging Guianan bearded sakis (Chiropotes sagulatus) in Guyana. The study group consisted of at least 65 individuals but showed a high degree of flexibility in grouping patterns (mean group size 39 ± 10). They were highly active, spending ca. 70% of their diurnal activity budget traveling and feeding. Activity patterns were relatively consistent throughout the year, although time spent feeding correlated significantly with fruit availability. The most common social behaviors were social resting and grooming. Agonism was rare (2.56% of social behavior) but did occur in the context of intergroup encounters, with males from the same group cooperating in intergroup agonism. Bearded sakis showed a high level of within group male affiliation, with male–male partners making up 65% of grooming dyads and males having another male as their nearest-neighbor 66% of the time. These results show that bearded sakis are characterized by egalitarian male–male and male–female relationships, highly fluid group sizes, and high levels of male affiliation. Similarities in the social behavior of bearded sakis and muriquis suggest several possible explanations for male–male bonding including cooperative defense of females from other groups, kinship, and maintenance of social cohesion after subgroup coalescence.