Helping as a signal and the effect of a potential audience during provisioning visits in a cooperative bird

Abstract

Research on cooperative breeding has begun to focus on direct fitness benefits gained by helpers, particularly when individuals are unrelated to those they assist. There has been considerable interest in helping possibly operating as a signal, either to show off individual quality to potential mates ('social prestige') or to ensure group membership ('pay to stay'). However, empirical investigation of these phenomena remains sparse. Here we investigate the potential for signalling via provisioning behaviour in the bell miner, 'Manorina melanophrys', an obligate cooperative breeding species in which the predominantly male helpers are commonly unrelated to breeders. Aggression between birds was extremely rare, and there was little to indicate a pay to stay system. The presence versus absence of members of the breeding pair as a potential audience at the nest had little influence on helper behaviour (e.g. load size/composition, visit duration or frequency). Helpers did produce more individually distinctive vocalizations when in the presence of another helper or the breeding male, although presence of the breeding female (a likely target of male signals) surprisingly had no effect. There was also evidence that nest arrival times coincided somewhat. These results are probably best explained by the helpers and breeding males being involved in additional cooperative behaviours when away from the nest, such as mobbing. Overall, there does not appear to be any evidence that bell miner helpers use nestling provisioning to signal their quality and/or work rate to one another or to either member of the breeding pair.