Introduction

A communication network is formed when more than one receiver can intercept the signal produced by a signaller, and when more than one signal reaches a receiver at the same time (McGregor & Dabelsteen, 1996). Communication network theory broadens the consideration of selection pressures on signallers and receivers to include selection on signallers by receivers other than the primary or target receiver, and selection on receivers when they receive more than one signal simultaneously or intercept a signal that was not targeted at them (McGregor & Dabelsteen, 1996; McGregor & Peake, 2000).

A mudflat full of male fiddler crabs (genus Uca, family Ocypodidae), all rhythmically waving their enlarged claw, seems a perfect example of a communication network: there are several signallers and receivers in close proximity, and many signals are being produced simultaneously. However, this human perception of a coordinated network may be partly a product of our excellent visual ability and large size in relation to these small crabs. What about the crabs themselves: how many receivers does a signal reach, and how many signals can individuals receive simultaneously? Is our impression that they form signalling networks simply an illusion caused by our extreme size and high visual acuity? Most importantly, what can we learn about the communication system of fiddler crabs by considering networks of signallers and receivers rather than simple sender–receiver dyads?