Call combinations, vocal exchanges and interparty movement in wild bonobos

The vocal repertoire of nonhuman primates is largely fixed. Individuals produce their species-specific vocalizations from a young age, and do not acquire new call types over their lifetime. Despite these limitations, however, monkeys and apes are able to increase their vocal flexibility in several ways, including subtle acoustic modification, call combinations, turn-taking and call persistence. Although primates have been observed to utilize these communicative features, the extent to which they integrate these abilities is not known. Here we show that certain long-distance calls produced by wild bonobos, Pan paniscus, assimilate several aspects of vocal flexibility in ways not previously documented in nonhuman primates. Communication between foraging parties exhibits context-specific call combinations relating to the movement of caller, call modifications that potentially target particular individuals, call-and-answer exchanges in which the initial caller's behaviour depends on the listener's reply, and possible persistence in call production. The selective pressure exerted by bonobos' fission-fusion social structure has likely favoured the integration of these communicative capabilities.