Absence of specific individuals and high food abundance elicit food calls in wild western gorillas

Food calls are widespread across many mammal and bird species, but the reasons of this adaptive success are not yet fully understood. Using data from four habituated groups of western gorillas ( Gorilla gorilla ) in Central Africa, we investigated the possible influence of ecological (food type and quantity) and social factors (presence, arrival and departure of specific group members) on food call production. Western gorillas emitted food calls mainly in foraging contexts. The emission probability increased with food types of high quality (in relation to the season) and, particularly, with abundant food patches. Food calls elicited the arrival of group members at the feeding tree. Adult females, the most frequent signallers, mostly emitted food calls when the silverback and all offspring were absent at the feeding tree, when compared to the absence of other group members. From the receiver perspective, the probability that the silverback and all offspring arrived at the feeding tree increased when adult females emitted food calls. When calling, adult females likely benefit by increasing both nutritional intake and protection of their own offspring (by increasing spatial proximity with the silverback). Moreover, food calls emitted in the second part of the duration of tree visits had the strongest effect on the prolongation of the feeding session. Our results suggest that the adaptive reasons of food calls in one-male harem species may be increasing group cohesion/coordination and facilitating offspring survival. Significance statement The adaptive reasons for the widespread presence of food calls in many animal species aremultiple and not mutually exclusive. We showed that western gorilla emitted food calls mainly in foraging contexts; they attract other group members and deliver information on the presence of abundant resources of high quality. Food calls emitted in the second part of the tree visit seem to prolong the feeding session. Adult females, the most frequent signallers, emitted food calls more often when their offspring and the silverback are absent. These results suggest that, in species with rather stable society (such as one-male harem), this behaviour may serve to increase cohesion/coordination and to facilitate offspring survival. This study is a first step for increasing our understanding on the presence of functionally referential calls in wild western gorillas.