Begging is an honest signal of hunger in a communally nesting bird with low genetic relatedness

Abstract: Kin selection theory predicts that conflict over resource allocation will intensify as relatedness between dependent young and adult caregivers decreases. As inclusive fitness constraints on dishonest signalling relax, begging behaviour is less likely to be a reliable indicator of hunger or condition. Therefore, dishonest signalling is expected to be especially prevalent in communally breeding species, for which offspring survival often depends on care from both related and unrelated adults. We evaluated the scope for conflict and its consequences for dishonest signalling in the greater ani (Crotophaga major), a communally nesting cuckoo in which multiple unrelated pairs lay in the same nest. Using video recordings of nearly 2500 feeding events across 10 nests, we demonstrate that begging behaviour is a reliable signal of hunger, with hungrier nestlings begging more intensely. We also show that begging may communicate reliable information about condition in the long term, with smaller nestlings begging more intensely than their larger broodmates. Ultimately, larger nestlings and those who begged more intensely were more likely to receive food, indicating that both begging signals and scramble competition influence resource allocation. Together, our results indicate that honest begging signals can persist even when caregivers and young are unrelated. Significance statement: Offspring solicit food from their adult caregivers through a variety of begging behaviours. These behaviours can convey important information about offspring hunger and/or long-term condition, but may be exaggerated, if offspring attempt to gain more than their proportionate share of resources. We examined whether offspring exaggerate their begging behaviour, such that it is not a reliable indicator of their hunger or condition, in the greater ani. Greater anis breed communally, with multiple pairs sharing a single nest simultaneously such that nestlings are fed by both their parents and unrelated adult caregivers. Theory predicts that begging should be less reliable if offspring and caregivers are unrelated, but we found that greater ani begging behaviour reliably communicated hunger, and potentially long-term condition, to adults. This study is the first to evaluate begging signal reliability in a communally breeding species.