Adult vocalizations during provisioning: offspring response and postfledging benefits in wild pied babblers

When provisioning offspring many bird parents give specific calls, which typically stimulate begging. Previous studies have investigated the benefits of food calling during the nestling phase, however, there is a current paucity of data on the use of food calls after young have fledged. This study describes the use of 'purr' calls, given by adult pied babblers, Turdoides bicolor, when feeding both nestlings and fledglings. Offspring associated these calls with food delivery: nestlings begged in response to experimental playbacks of purr calls; whereas fledglings, which were no longer confined to the nest, approached calling adults. As well as with feeds, adults also gave purr calls in nonfeeding contexts. Playbacks of purr calls given in feeding and nonfeeding contexts elicited the same responses, suggesting that offspring expected food when they responded to both 'feed' and 'no-feed' purr calls. Adults seemed to use the association between purr calls and food delivery by giving no-feed purr calls to promote fledgling movement, for example when leading young away from predators. Fledglings directly benefited when they approached adults who gave no-feed purr calls, despite not receiving any food. This study raises the possibility that food calling during the fledgling phase is a widespread, but understudied form of parent-offspring communication in birds and may be a more important aspect of avian parental care than is currently realized.