Acoustic communication in crocodiles: How do juvenile calls code information?

Abstract

In spite of its importance for the understanding of the evolution of sound communication, information concerning the vocal world of crocodilians is limited. Experimental works have brought evidence of the biological roles of juvenile sound signals, with “hatching calls” eliciting care by the mother and synchronizing clutch hatching, “contact calls” gathering groups of juveniles, and “distress calls” inducing maternal protection. Recently, we investigated the question of species-specific information coding within juvenile calls. The analysis of signal acoustic structure shows inter-specific differences between calls. However, using playback experiments, we bring the evidence that these differences are not relevant to animals, either juveniles or adults. By using calls modified in the temporal and the frequency domains, we isolate the acoustic cues necessary to elicit a behavioral response from receivers, underlying the importance of the frequency modulation slope. Considering previous results underlying the absence of information about individual identity in juvenile calls, we make the hypothesis that these signals basically support a “crocodilian” identity.