Azorean rock-pool blennies produce size-dependent calls in a courtship context

Male calling or singing behaviour often plays a crucial role in competition among males and attraction of females. We studied the occurrence of male calls in a paternal nest-guarding fish, the rock-pool blenny. We found that males often produced calls when a female entered their nest burrow and during her visit inside the burrow. The dominant grunt-like part of these calls has a fundamental frequency of about 30 Hz and generally contains one to six harmonics. This harmonic component is typically preceded by a short introductory component and often followed by an even shorter terminal component, both of relatively low amplitude and irregular spectral composition. The fundamental frequency differs consistently between males and is negatively correlated with male size. Consequently, spectral features of the calls may be used in female mate choice during the female's decision to stay in a burrow and spawn. Not all males that were observed during a female visit produced calls, nor did calling males call during all female visits. The number of calls during a visit varied within and between males and ranged from 1 to 13. Calling may express some male mate preference when calls are selectively produced during visits of preferred large females. However, we did not find any evidence for differences in calling activity towards three female size classes, nor was there an effect of male size. This is one of the first reports in the literature on the use of sounds in blenny courtship behaviour and adds to a growing body of evidence revealing the communicative importance of acoustic signals in a wide variety of fish taxa.