Chimpanzee food calls provide information about the value and type of food: a playback study

Abstract Functionally referential signals are taxonomically widespread but vary greatly in the specificity of information they convey to receivers. Chimpanzee food calls indicate the relative preference value of the eliciting food in a way that is intelligible to receivers, but whether their specificity extends further than this, to individual food types within preference categories, has not been empirically tested. Here, we sought to extend these previous findings using acoustic analyses and playback experiments to determine (a) whether food calls elicited by foods with similar preference values (i.e. multiple high value foods) are acoustically discriminable from one another, and (b) whether this information is intelligible to receivers. Our acoustic analysis indicated acoustic differences between calls associated with both high and low preference foods, and the foods within each of those categories. Crucially, our playback experiment demonstrated this highly specific information regarding the referent was also accessible to the receiver. Specifically, our subject was able to discriminate between calls elicited by (i) high and low value foods, (ii) individual types of high value food, and (iii) individual types of low value food. This represents an unprecedented degree of specificity in referential food calls of our closest living relatives, which has previously not been identified outside of alarm call systems.