On the evolution of delayed recruitment to food bonanzas

Whereas food sharing by immediate recruitment to food bonanzas is relativel y common, especially among birds, delayed recruitment from overnight roosts is comparatively rare, although it has been studied extensively in the com mon raven (Corvus corax). Two hypotheses have been advanced to explain the evolution of delayed recruitment. Under the status-enhancement hypothesis, delayed recruiting is favored because the recruiter's social status increas es with the number of followers it leads to a food source. The posse hypoth esis also focuses on the number of individuals recruited to a site, but in this case aggregation is favored because larger groups are more likely to u surp a carcass defended by a pair of territorial adult ravens. We used a ga me-theoretic model to explore the logic of immediate versus delayed recruit ment in the light of these hypotheses. In particular, we identified three c ritical values of the probability of immediate recruitment: that below whic h delayed recruitment is a cooperative strategy, that below which delayed r ecruitment is an evolutionarily stable strategy, and that below which a mut ant strategy of delayed recruitment will invade a population of immediate r ecruiters to reach fixation. The model demonstrates that either status enha ncement or the posse effect may alone suffice for the evolution of delayed recruitment to food bonanzas via mutualistic information sharing at communa l roosts.