Signaling of Need between Parents and Young: Parent-Offspring Conflict and Sibling Rivalry

Abstract

The young of birds and mammals frequently solicit food and other resources from their parents in ways that appear to be costly either in terms of energetic expenditure or because they may attract predators. Costly solicitation has been explained as a means by which the young manipulate their parents into providing more resources than the parental optimum. Alternatively, communication between parents and young can be interpreted as an evolutionarily stable signaling system. A model is developed of two young in a brood who compete for a fixed amount of resources distributed by their parents. It is shown that an evolutionarily stable signaling system can exist in which the parent obtains accurate information about the resource needs of its young and on which it bases its resource distribution decisions. Young with greater resource requirements solicit at higher levels, but the system is stable because any misrepresentation is selected against. Essential for stability is that signaling must be costly; it is the costs that penalize misrepresentation and allow stability. The necessity of costs for a stable signaling system is a direct result of potential parent-offspring conflict over resource share. The model is used to investigate the influence on expected levels of solicitation of within-brood relatedness, the condition of the offspring and the offspring's brood mate, and the total amount of resources available for the brood. The cases of identical and nonidentical young are considered. The basic model is extended to study situations in which the costs of solicitation are experienced by both brood members and to offer a preliminary analysis of the joint effects of within- and between-brood competition for resources.