Variation in initiator strategy in fighting by silvereyes

Abstract

Abstract. Silvereyes, Zosterops lateralis, initiate agonistic interactions for access to food using 10 different elements of threat display, attack, vocalization and aerial combat. Qualitative variation in the strategies used by initiators was examined in interactions, after short-term food deprivation, between members of 10 caged winter flocks in which membership and dominance relationships had been stable for 3 months. Differences in strategy were independent of initiator rank per se but were related to the dominance relationship and rank distance between initiator and opponent. Hunger motivation and the degree of familiarity of contestants were also significant influences. An experimental manipulation of flock membership confirmed that strategy changed as position in the hierarchy changed. Threat display and attack are alternative strategies adopted in different situations and are associated with different probabilities of winning. A model based on a multidimensional scaling analysis of the patterns of co-occurrence of the 10 elements is reported. It is concluded that costs and benefits of participating in an interaction differ for individuals and that those costs are associated with performance, the probability of submission or retaliation by the opponent and, thus, access to food. Different elements of threat display and attack signal variations in the ratio of potential and actual costs and benefits of fighting to the initiating individual.