Sibling negotiation

Current discussions of offspring begging typically assume eitherthat it is a signal directed at parents or that it representsa form of scramble competition to gain access to them. However,offspring might also display to inform nest mates that theywill contest the next food item to be delivered; in other words,begging (possibly in the absence of parents) might serve purelyas a form of negotiation among siblings. Here, we develop agame-theoretical model of this possibility. We assume that offspringvary in their need for food, which influences how intenselythey compete for access to parents. Before parental arrival,however, young may exchange signals informing each other oftheir state, and these signals may influence their subsequentcompetitive behavior. We focus on the possibility that a costlydisplay during the "negotiation" phase can serve to inform rivalsof a chick's need for resources and thereby deter them fromcompeting intensely when the parent arrives. We show that thisform of negotiation is more likely to prove stable when thefood delivered by parents is indivisible, and when it is hardfor one chick to monopolize access to resources. Investmentin negotiation (as opposed to competition) is predicted to increasewith nestling relatedness; in addition, all other things beingequal, hungrier chicks are expected to invest relatively moreeffort in displaying to their rivals, whereas weaker or smallerchicks are expected to invest less.