Recruitment calling: a novel form of extended parental care in an altricial species.

In many altricial birds, fledglings disperse when they are no longer fed, and this dispersal marks the end of parental care. In some species, however, young remain in close association with their parents after nutritional independence. Because juveniles are still inferior foragers at this stage, they might benefit from parental assistance in locating good feeding sites, but this possibility remains largely unexplored. Here, we show that parents and helpers in pied babbler (Turdoides bicolor) societies use a recruitment call to direct nutritionally independent, but inexperienced, foragers to particular food patches. Observations and a playback experiment indicated that adult babblers use a "purr" call to recruit group members to a foraging patch. Creation of experimental foraging patches supported observations that individuals tend to give the call when they are foraging on abundant, divisible food sources and when their group contains independent fledglings (youngsters who are no longer fed directly). Fledglings responded to calls more often than adults, who frequently encountered aggression from the caller if they did, and the fledglings gained significant foraging benefits. This is the first study to demonstrate that altricial birds may use recruitment calls to extend parental care past the period of direct provisioning.