Food-solicitation displays in nestling birds: still begging for answers

Nestling begging is a key model for understanding animal communication and parent-offspring conflict. Dynamic begging displays are often interpreted as costly, honest signals of need, with honesty maintained by viability costs, as proposed in Godfray's influential signalling model. However, this framework has faced increasing theoretical criticism and mixed empirical support. Here, we reassess three core predictions of the honest-signalling framework. First, experimental evidence strongly supports begging as a signal of short-term hunger, but evidence that it reliably reflects long-term need or intrinsic quality is limited. Begging is also highly plastic, varying with prior experience, nestmate and parental behaviour, body temperature, brood size and other contextual factors. This raises questions about the precision and information content of the display. Second, although parents often increase provisioning in response to collective begging, food allocation within broods is frequently influenced by non-begging cues such as size, position and colouration, and intense begging is not invariably rewarded. Sibling responses are also more diverse than predicted by purely competitive models, encompassing escalation, de-escalation, negotiation and potentially prosocial coordination. Third, empirical support for direct costs of begging, particularly predation and physiological costs, remains weak or inconsistent, whereas indirect inclusive-fitness trade-offs appear more plausible. Together, these findings challenge assumptions of fully informative signals, invariant parental responsiveness and necessary direct signalling costs. We argue that future work should move beyond traditional signalling and scramble-competition models by incorporating parental flexibility, receiver inattention, learning, signal and response plasticity, and family-level rather than dyadic parent-offspring interactions. We also outline conceptual and empirical avenues that may facilitate progress, highlighting a field that remains rich in unresolved questions and opportunities for future research.