Signalling for food and sex? Begging by reproductive female white-throated magpie-jays

Food begging is common in nutritionally dependent young of many animals, but structurally homologous calls recur in adult signal repertoires of many species. We propose eight functional hypotheses for begging in adults; these stem from observations in birds but apply broadly to other taxa in which begging occurs. Adult cooperatively breeding white-throated magpie-jays, Calocitta formosa, use loud begging vocalizations, particularly near the nest site during reproduction. We analysed the social context and behavioural phenology of loud calling and allofeeding in this species and compared these with predictions from each functional hypothesis. We found that reproductive females were the primary producers of beg calls, and their begging peaked during the fertile period when reproductive conflict among males and females was highest. Loud begging rates correlated positively with provisioning rates, but females called more in the pre-incubation fertile period than they did after they had initiated incubation. Based on the context, phenology and active space of the signal, we conclude that female loud begging vocalizations function to signal nutritional need to group members, but also have been evolutionarily co-opted to advertise fertility to potential extrapair partners. The location of calling is probably a consequence of nest guarding by breeding females to prevent intraspecific brood parasitism.