Soft calls and broadcast calls in the corncrake as adaptations to short and long range communication

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“…If the acoustic structure of F calls or rumble calls was compared with G calls, the choice of the vocalization for aggressive signaling was not a simple decision between a soft and loud signal but also involved a decision between a high-and a low-frequency signal. Moreover, in the Corn Crake, the maximum limit for communication distance with soft calls was significantly shorter than that of loud calls, if played at the same amplitude, which suggests that the acoustic structure of soft vocalizations was used to limit the range of the signal (Ręk 2013b). Consequently, these results are consistent with a previous report that suggested that soft vocalizations are something more than low-amplitude signals (Ręk 2013b(Ręk , 2014.…”

“…Moreover, in the Corn Crake, the maximum limit for communication distance with soft calls was significantly shorter than that of loud calls, if played at the same amplitude, which suggests that the acoustic structure of soft vocalizations was used to limit the range of the signal (Ręk 2013b). Consequently, these results are consistent with a previous report that suggested that soft vocalizations are something more than low-amplitude signals (Ręk 2013b(Ręk , 2014. Thus far, the 3 major categories of soft vocalizations have been described as follows: structurally distinct soft vocalizations, low-amplitude variants of normal vocalizations, and normal vocalizations with additional lowamplitude components (for a review, see Searcy et al 2014).…”

Do aggressive signals evolve towards higher reliability or lower costs of assessment?

“…It has been shown that the reliability of this signal is maintained by a receiver retaliation rule, rather than by inherent costs (Ręk & Osiejuk, ), which means that it can be beneficial for receivers to respond to soft calls indiscriminately, that is, regardless of their acoustic structure. Nevertheless, the frequency spectrum of gurgling notes limits their range (Ręk, ), most likely because it is physically difficult or costly for a small bird to produce low‐frequency sounds with a high amplitude (Fletcher, ), which suggests that the structure of soft calls may encode some extra information, with reliability being maintained by an inherent cost. Such physical associations have been shown to be provide important information for receivers in sexual contexts (Vannoni & McElligott, ; Wagner, ).…”

Habitat complexity and the structure of vocalizations: a test of the acoustic adaptation hypothesis in three rail species (Rallidae)

“…Therefore, in optimal conditions Corncrake calls propagate for long distances and males can be heard from at least 1 km (Schäffer & Koffijberg ). Previous research on the Corncrake showed that its calls, with wide frequency spectrum and repeated pulse structure, are remarkably resistant to degradation in their optimal habitat (Ręk & Osiejuk , Ręk ), and a similar effect has been observed for many species inhabiting grasslands (Wiley ). Nevertheless, Corncrake calls were degraded more than calls of Water Rail and Spotted Crake while transmitted through the partially flooded habitat with a more complex vegetation composition.…”

“…Indeed, a number of studies have already demonstrated that birds do not maximize the active space of their vocalizations but that acoustic parameters, such as amplitude, are individually adjusted based on social context and environmental conditions (reviewed in Catchpole & Slater ). Nevertheless, even when controlling for the amplitude, signals may still attenuate and degrade at different rates (Ręk ). In more complex habitats, where more effects that might potentially cause attenuation and degradation co‐occur and longer transmission must incur higher energetic cost, signals should attenuate faster and have shorter transmission ranges.…”