Escalated begging does not compromise nestling health.

Abstract

A widely accepted explanation for the reliability of offspring begging signals assumes a differential benefit model balanced by direct viability costs independent of offspring nutritional condition. However, supporting evidence for this idea is inconclusive and often hampered by methodological limitations, including differential stimulation protocols and reliance on single, potentially biased markers of nestling health. This study tested the existence of direct, intrinsic, and condition-independent allocation trade-offs between begging and body mass, immunity and oxidative stress by manipulating the begging effort of spotless starling (Sturnus unicolor) nestlings while maintaining constant food intake. We addressed potential problems of previous experimental protocols, ensuring uniform stimulation levels and evaluating multiple immune and oxidative markers. We observed no significant effects of experimentally increased begging effort in any of the 14 physiological markers analyzed, with 95% confidence intervals of effect sizes consistently including zero or one (for the lysis capacity of plasma), indicating no biologically relevant effects. Overall, our findings suggest no physiological trade-offs associated with intense begging.