Eavesdropping and animal conflict

Fights between pairs of animals frequently take place within a wider social context. The displays exchanged during conflict, and the outcome of an enc ounter, are often detectable by individuals who are not immediately involve d. In at least some species, such bystanders are known to eavesdrop on cont ests between others, and to modify their behavior toward the contestants in response to the observed interaction. Here, I extend Maynard Smith's well known model of animal aggression, the Hawk-Dove game, to incorporate the po ssibility of eavesdroppers. I show that some eavesdropping is favored whene ver the cost of losing an escalated fight exceeds the value of the conteste d resource, and that its equilibrium frequency is greatest when costs are r elatively high. Eavesdropping reduces the risk of escalated conflict relati ve to that expected by chance, given the level of aggression in the populat ion. However, it also promotes increased aggression, because it enhances th e value of victory. The net result is that escalated conflicts are predicte d to occur more frequently when eavesdropping is possible.