Males from the family Batrachoididae are thought to facilitate vocal activity from their neighbours with their advertisement mating calls. As other batrachoidids, Lusitanian toadfish males emit an advertisement call (the boatwhistle) to attract mates. Here, we investigate vocal interactions between males in small aggregations. We recorded groups of six males that spontaneously occupied artificial concrete nests in an intertidal area of the Tagus River estuary (Portugal). The number of boatwhistles produced by each male was tallied for each 5 min interval of several periods of one hour. Boatwhistle occurrences were not adjustable to a Poisson distribution indicating that toadfish did not call at random. Correlation analysis (non-parametric Gamma correlation) showed that some males positively influenced other males to call while others suppressed the calling activity of neighbours. Consistently, the number of boatwhistles produced per male was not correlated with the number of calling males contradicting the vocal facilitation hypothesis. The effect of a neighbour’s calling activity was further tested with playback experiments. Sound playback consisted of boatwhistles (BW) emitted at a rate of 5 or 20 BW/min or of white noise (20 sounds per min). Males (n=8) showed a tendency to mimic the neighbours’ calling rate, when subjects were calling at a high rate (>12 BW/min). However, subject males were indifferent to low and inhibited by high playback rate if they were initially calling at a low rate (<12 BW/min). These preliminary results suggest that Lusitanian toadfish males respond differentially to other males depending on their own motivation (i.e. calling rate), indicating that vocal interactions among Lusitanian toadfish breeding males are more complex than initially thought.
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