Bonobos use call combinations to facilitate inter-party travel recruitment

Abstract

Many primates produce vocalizations when initiating travel. These “travel calls” are often acoustically similar to vocalizations unrelated to travel, and listeners appear to rely on a shared context with callers to correctly interpret the calls. When individuals use vocalizations to coordinate movement with out-of-sight group mates, however, such pragmatic cues are unavailable. Under these circumstances, effective communication may depend on more informative acoustic signals. Here, we investigate travel-related vocalizations that occur when callers and listeners cannot see one another: long-distance calls given by wild bonobos (Pan paniscus). We find that production of a specific call combination, the “low hoot-high hoot,” is more likely than a high hoot alone to be produced prior to travel. Furthermore, the low hoot-high hoot combination is more likely to result in inter-party recruitment—that is, individuals from other parties are more likely to approach the caller. We also compare these observations with previous research and find that bonobos appear to use distinct call combinations to facilitate specific movement patterns common in fission-fusion social structures. These results suggest that use of call combinations allow bonobos to convey more specific information than do single call types alone and that this additional information allows for effective communication between out-of-sight parties.