Call combinations in wild chimpanzees

By combining different call types, such as barks with screams, individuals have the potential to vastly increase the range of information that can be decoded by listeners. Few animal studies, however, have examined the information content of call combinations compared with the information conveyed by each call singularly. We examined several aspects of call combinations in the repertoire of wild chimpanzees in the Tai Forest, Ivory Coast, including the types of combinations, the contexts and possible functions and compared these with the use of single calls. Almost half of all vocalisations produced by the Tai chimpanzees occurred in combination with other vocalisations or with drumming. A total of 88 different types of combinations were used. Single calls and call combinations were each produced in specific contexts. The contexts in which six of ten combinations were produced differed from the contexts of at least one of the component calls. The contexts in which the combinations were produced varied from the component calls in five different ways, three having potentially novel functions. Two of the three may have an additive function, such that two pieces of information can be conveyed simultaneously, increasing message complexity. This analysis clearly shows that call combinations are an important part of chimpanzee communication. The implications with regard to the evolution of human language are discussed. Testing of the information conveyed by single calls and of call combinations, using playback experiments, is advocated.