Temporal patterns of broadcast calls in the corncrake encode information arbitrarily

By combining different vocalizations, in different ways, animals have the potential to vastly increase the range of information that can be encoded in acoustic signals. Although such a mechanism is hard to apply in species having small repertoires, individuals can increase the amount of information by separating vocalizations with intervals of different length, that is, with vocalizations functioning as commas and intervals as carriers of information. Nevertheless, there has been little study of information encoding using temporal arrangement of single call types. We have recently shown that male corncrakes (Crex crex) produce such temporal patterns in correlation to their aggressive motivation and these elicit the according behavior in the receivers. In this study, we report that the design of these patterns is arbitrarily related to their function. The aggressive information is encoded in the syntactic pattern itself, not in the absolute length of intervals, and thus signal variants appear to transfer different kinds of information without any association with the structure of signal variants. The finding of such coding in acoustic signaling in species with innately programmed call structures implies a much larger flexibility and complexity of communication systems of animals in general and in species with low repertoires of genetically coded vocalizations in particular.