Forewarned is forearmed: early signals of RHP predict opponent fatigue in hermit crab shell fights

In animal contests, opponents often perform repeated displays that are assumed to advertise their stamina and thereby fighting ability. However, given the severe time and energetic constraints imposed by such displays, we hypothesized that separate signals, performed early in a fight, may be used to reduce subsequent costs. We investigated whether the amount of cheliped flicks performed by a defending hermit crab during a prefight assessment period was indicative of the performance capacity of the defender and whether the frequency of flicks predicted the subsequent outcome of contests. Defenders that won fights by retaining their shells produced more vigorous flicking than those that were evicted. There was a strong trend between the rate of flicking performed by the defender and the maximum speed attained in performance capacity trials. Further, the rate of flicking was positively correlated with the duration of pauses that attackers left between bouts of shell-rapping, an indicator of attacker fatigue. Thus, these displays might inform the attacker about the potential persistence of the defender and therefore about the likely costs that the attacker will incur. Indeed, the rate of flicking performed by defenders early in the fight strongly predicts the eventual outcome of the contest.