Begging scrambles with unequal chicks: interactions between need and competitive ability

When offspring compete for the attentions of provisioning parents, empirical and theoretical work has generally concluded that chicks honestly signal their need for resources and that parents control allocation. Here, we develop models to show that when allocation of food resources is determined by competitive begging scrambles between sibs, the offspring's ESS begging levels, shares of food and personal fitness gained will be determined by an interaction between their competitive abilities and their true needs. Many of the predictions of this scramble competition model are qualitatively very similar to models of honest signalling of need, where parents, not offspring, control the allocation of food. Consequently, it will be difficult to distinguish between the two mechanisms of food allocation based on empirical observations of the responses of chicks to feeding by parents.