Foraging and mating opportunities influence refuge use in the fiddler crab, Uca mjoebergi

Although many animals use refuges to avoid predators, it is often costly to do so. The longer an individual remains in a refuge, the less time it has available for other essential activities, such as foraging and mate searching. Animals should therefore optimize the time spent in a refuge after an attack by adopting a flexible approach to predator avoidance. I examined refuge use in the fiddler crab, Uca mjoebergi, under variable foraging and mating contexts on a mudflat in Australia. There were no sex or size differences in refuge use, suggesting that there are no morphological or gender biases in predation risk. Risk-taking behaviour in U. mjoebergi was, however, highly flexible and appeared to be strongly dependent on the trade-off between the costs and benefits of hiding. Refuge use varied between optimal foraging and reproductive periods of a semilunar cycle. Loss of foraging time influenced risk-taking behaviour in both males and females since both were quicker to re-emerge when food levels were high. During the reproductive period, crabs took longer to re-emerge because of few foraging opportunities, as well as few mating opportunities since receptive females were rare. However, when mating opportunities for males were experimentally increased by introducing a tethered female, actively courting males engaged in highly risky behaviour and re-emerged after a few seconds, with some males abandoning refuge use completely. Refuge use in U. mjoebergi is therefore highly flexible, with the decision to re-emerge influenced by fitness benefits.