Abstract
In many primate species, individuals produce a finite number of acoustically distinct calls as part of a species-specific vocal repertoire. The calls usually have context-specific functions, such as defending a home range, avoiding predators, or alerting conspecifics to a food source, etc. In some primates, call systems are structurally more complex because calls are assembled into higher-order level of sequences that sometimes carry specific meanings. Here, we describe a specific vocal acoustical structure which revealed a high level of combination of finite vocal unit in sequences. We conducted focal animal samples method in three habituated groups of Olive colobus monkeys (Procolobus verus). Three call combination types in sequence were found composed from two to five call units. Some of these call combinations were linked to specific contexts. Our study thus provides further evidence that the propensity to combine acoustic units into higher order sequences is not an exclusively human trait but a behavioural feature that may be widespread in the primate communication.