Effectiveness of multi-component, dynamic begging displays as honest signals of nestling hunger

Parent–offspring communication depends on offspring signals that help parents assess need and allocate care. Nestling begging is often treated as a graded, information-rich and therefore honest signal of hunger, as predicted by costly signalling models. We quantified how effectively visual and acoustic begging components encode food deprivation in spotless starling (Sturnus unicolor) nestlings using field observations and a controlled laboratory experiment. We combined random-regression models with information-theoretic measures of uncertainty reduction and receiver-based machine-learning decoding. In wild broods, begging order and maximum postural intensity increased with deprivation time, yet posture and calling together reduced uncertainty about deprivation by less than 5%. Distinct postural levels overlapped widely among deprivation states and followed a stereotyped sequence—rapid escalation to maximum intensity followed by relaxation—yielding poor resolution of intermediate hunger. Adding components improved decoding only marginally beyond the first few cues. Parental allocation was correspondingly rapid, although display duration could provide additional information once the full bout was perceived. Discrete coding analyses confirmed that simple postural schemes were most consistent and that begging reliably distinguished only coarse, extreme hunger states. Overall, the results support partially informative (pooling) or attention-seeking signalling models in which parents rely on a small set of salient cues within a multi-component display.