Food-associated vocalizations in mammals and birds: What do these calls really mean?

Alarm calls and food-associated calls from a diverse range of species are said to be functionally referential, in that receivers can use these sounds to predict environmental events in the absence of other contextual cues. The evolutionary driver for referential alarm calls has been hypothesized to be the mutually incompatible escape behaviours required to avoid different predators. However, some species produce acoustically distinctive and referential alarm calls but do not show highly referential abilities in other domains. We examined whether food-associated calls in many species are likely to be functionally referential and whether they specifically communicate about characteristic features of food. Food-associated calls are given in both feeding and nonfeeding contexts, and the types of information contained vary greatly. Most species do not produce unique calls for different foods; more common is variation in the call rate, which suggests that call structure reflects the callers' internal state rather than the food type. We also examined the ultimate function of food-associated calls to evaluate whether there is a unifying explanation for the evolution of functionally referential food calls. Based on the literature, there does not appear to be a unifying function. In conclusion, while functionally referential food-associated calls have been convincingly demonstrated in a few species, it is more common for these vocalizations to reflect arousal rather than additionally providing specific referential information about the feeding event. At this point, there is no compelling hypothesis to explain the evolution of functionally referential food-associated calls. Given the multiple functions of food-associated signals, we should not expect a unitary explanation.