Vocal begging by nestlings and vulnerability to nest predation in Meadow Pipits Anthus pratensis; to what extent do predation costs of begging exist?



Models of the evolution of parent-offspring communication and of brood size assume that the noisy begging by the young is costly in terms of predation. The present study was designed to investigate cause-and-effect relations between the behaviour of the offspring and adult Meadow Pipits Anthus pratensis and the risk of nest predation. Harriers (Circus spp.), which can use auditory signals, were the main predators in the study area. I found that the intensity of vocal begging by broods did not influence their survival, despite the fact that the proportion of time that parents sacrificed to nest guarding declined with increased begging and some broods readily begged if a stimulus resembling the approaching parent was produced. The lack of fitness penalties for noisy broods was attributed to the following factors: (1) the open habitat was easy to scan, and parents silenced the young before feeding them if a predator was close (this adaptation was demonstrated in an experiment) and (2) parent birds could not deter harriers searching for prey, and therefore nest guarding did not influence the probability of nest detection. Pitfalls in the interpretation of relations between the vocal begging and the vulnerability to nest predation are discussed.