Nestling begging increases predation risk, regardless of spectral characteristics or avian mobbing

Abstract

Models of parent–offspring conflict and nestling begging honesty often assume that signaling is associated with increased predation risk. However, little evidence exists that begging actually increases predation in the context in which it evolved, especially when the potentially modulating effects of parental defense are taken into account. We measured the cost of begging in cooperatively breeding bell miners ('Manorina melanophrys') by baiting 168 inactive nests with a wax egg and broadcasting sounds from nearby speakers. Nests were randomly assigned to 1 of 3 treatments: silence, unmanipulated begging calls, or shaped white noise pulses that matched the amplitude envelope of each corresponding begging call. Moreover, half of the nests were placed outside and half inside bell miner colonies, where miners vigorously mob potential nest predators. Predation was not influenced by vegetation cover, distance of the nest from the speaker, or placement inside the colony. Sounds were costly, however, as nests broadcasting begging signals or white noise were predated more often and more quickly than silent controls. Contrary to theoretical predictions regarding "stealthy" design, we found that predators were just as likely to locate nests with broadband white noise playback as nests broadcasting begging signals. Further, there was an interaction between playback amplitude and predator type (avian vs. rodent): Louder playback led to decreased nest survival for those taken by avian predators. As increased begging drives provisioning rates in many species, including bell miners, this reveals an inescapable trade-off between nestling begging intensity, parental provisioning effort, and predation risk.