SCREAMING AS A STRATEGY TO REDUCE THE PREDATION RISK INCURRED BY BEGGING?

Following the theory of parent-offspring conflict parents request from their offspring an honest signal of food requirement to optimally adjust feeding rate. For this purpose, offspring display a highly informative signalling system, begging vocalisation, for which the conspicuousness to predators maintains honesty, since only hungry offspring are willing to take this risk. The risk of predation incurred by begging activities challenges our understanding of how begging vocalisation could evolve towards a high degree of noisiness. A solution to this apparent paradox resides in the possibility that alongside the evolution of begging, birds also evolved strategies that reduce the risk of being depredated. Following the ornithological literature nestlings scream in the presence of a predator to frighten it, induce parents to rescue them and siblings to flee from the nest and hide in the vegetation. I therefore propose the hypothesis that nestling screaming behaviour evolved as a means of reducing the risk of predation incurred by conspicuous begging. Comparative analyses supported the prediction postulating that species in which nestlings scream in the presence of a predator produce begging calls that are more conspicuous to predators than calls of non-screaming species. This suggests that the predation cost of begging lies not only in terms of predation per se but also in the requirement of anti-predator strategies.