Helping has signalling characteristics in a cooperatively breeding bird

In a communication network, individuals can observe and gain information from behaviours not directed at them. In this context, behaviours not primarily intended to be a signal might evolve a secondary signalling function if they contain reliable information used by others for fitness decisions. We examined whether this could be the case for helping behaviour, since it can take place in a communication network, be associated with increased fitness benefits and be costly. We investigated whether helping has signalling characteristics in a colonial cooperative bird, the sociable weaver, Philetairus socius. We found that the behaviour of helpers increased their chances of being seen by other individuals when feeding, and was influenced by the audience and by the value of the prey brought to the nest. Specifically, helpers (1) spent longer than parents holding the prey at the colony before feeding; (2) fed the nestlings when the number of birds in the audience had increased; (3) spent longer holding their prey at the colony before feeding when they brought larger prey and (4) when rain and thus food was less abundant. We discuss whether these results can be explained by alternative hypotheses such as lower willingness to undertake predation risk by helpers. However, we suggest that helping has characteristics compatible with signalling and thus, in addition to the primary function of feeding young, helping behaviour might be used to convey information.