Vocal similarities and social bonds in Campbell's monkey (Cercopithecus campbelli).

This study examined variations of social call structures in female Campbell's monkeys. The comparison of frequency modulations using a similarity index revealed that each individual presented one to three variants. Some variants were shared by two to several individuals, often associated with play. On the contrary, vocal divergence was observed in a socially isolated animal and a negative correlation appeared between similarity index and the frequency of avoidance. This preliminary study gives the first evidence of variant sharing between group members in primates.