Near-synchronous calling in the hip-pocket frog Assa darlingtoni

Sustained perfect synchrony of signal production by animals is unrealistic, but even near-synchronous signalling is extremely rare. Near-synchronous signalling has been documented in some orthopteran insects and fireflies, and one kind of frog. This study provides observations and analyses of sustained bouts of impressive near-synchronous calling by a terrestrial breeding frog from Australia, the hip-pocket frog (Assa darlingtoni). Males called in scattered clusters of several individuals from the rainforest floor of northern New South Wales. In eight of nine pairs of semi-isolated males, there was sustained near-synchronous calling in bouts consisting of 16–20 calls and lasting 5–10 min. There was extensive overlap of the pulsed calls, and calls of a lagging male began overlapping that of a leading male after 2–5 pulses of a leader’s call note. In five pairs, one male’s calls were usually in the leading position; in three pairs, leadership frequently switched between males. In the latter interactions, males frequently skipped a call and produced its next call or calls in the leading position. This tactic has been interpreted as sexual competition between neighbours in orthopterans, but further research is required to rule out possible alternative hypotheses.