The two main theories of food-associated calls in animals propose functions either in cooperative recruitment or competitive spacing. However, not all social animals produce food calls and it is largely unclear under what circumstances this call type evolves. Sooty mangabeys Cercocebus atys do not have food calls, but they frequently produce grunts during foraging, their most common vocalisation.
In a subsequent field experiment we presented highly desired food items and found that discovering individuals called, unless harassed by competitors, but that the calls never attracted others, confirming that the grunts do not convey any information referential to food.
Our data thus suggest that the evolution of cooperative food calling is a two-step process, starting with increased motivation to vocalise in the feeding context, followed by the evolution of acoustic variants derived from context-general contact calls. This evolutionary transition may only occur in species that feed on clumped, high-quality resources where social feeding is competitive, a condition not met in sooty mangabeys.
Food-associated calls have been reported in many socially living avian and mammalian species Clay et al. The behaviour is interesting because it raises basic questions about signal evolution and call meaning, as well as the evolution of cooperative behaviour more generally. Despite much cross-disciplinary interest, however, comparatively little is known about the evolutionary emergence of food-associated calls in animal communication.
Importantly, not all social species produce food-associated calls but, in species where the behaviour has been reported, two main functions have been proposed. A first one states that calls advertise a food resource to other group members, a seemingly altruistic act and a form of food sharing.
