Wandering in male fiddler crabs (Uca tangeri): alternative reproductive tactic or a functional constraint?

The ‘aggressive wandering’ behaviour of male fiddler crabs is well documented in several species and is usually described as an apparently random movement through a population, punctuated by threats and combat directed at displaying males, and superficial burrow explorations. It has been suggested that wandering males are mainly low condition individuals with a regenerating major claw, unsuccessful at attracting mates, wandering through the population seeking surface copulations as an alternative to burrow copulations, which may be considered an alternative reproductive tactic. In order to test this hypothesis we have made several predictions. We observed several focal wandering males, compared sizes of wandering and resource holder individuals, and monitored their abundance across the lunar cycle. We did not observe any surface copulation attempts in any of our focal subjects. The number of burrows explored by wandering males was highly variable and not dependent on the subject’s size although larger males do spend more time superficially exploring burrows. Wandering males are significantly larger than burrow-holder males and there was a peak in wandering in the first moon quarter. We conclude that it is important to dissociate wandering from surface copulations and that wandering is not an alternative reproductive tactic for lower condition males. The number of wandering males across the lunar cycle still suggests that wandering may be related to mating and we discuss several ways in which it could be possible.