Julie THEVENET : The acoustic basis of information coding in crocodiles’ vocalizations

from September 1, 2019 to August 31, 2022
Date of thesis defence: 09 november 2022

laboratories : CRNL (Lyon) et ENES Neuro-PSI (Saint-Etienne)
thesis supervisors : Nicolas Grimault and Nicolas Mathevon

Summary : 

Acoustic communication is an essential communication channel for crocodiles. Indeed, they use acoustic signals throughout their lives, to ensure the survival of the juveniles and to interact socially. More in detail, previous studies showed that young crocodiles use a repertoire of graded signals: they use signals having similar basic acoustic structure to encode different messages. Nevertheless, observations show that these signals are treated as discrete rather than graded, i.e. the individuals’ behavioral responses seem to be stereotyped.

The main goal of this project is to understand how crocodiles perceive the graded system of signals and to study experimentally the principle of categorical perception. In depth studies will then determine which acoustic features crocodiles use to encode the information, and which of these features are used to discriminate between biological relevant signals. This project is based on an interdisciplinary approach combining acoustics, behavioral and physiological studies. Acoustic signal processing and synthesis work will be carried out throughout the thesis in order to manipulate relevant signals. Signals will be modified through acoustic morphing to test the categorization process. Different acoustic features will be then modified (F0, FM slope etc.) in order to estimate their functionality in signal segregation. These investigations will be conducted both in wild, through playback experiments, and in the laboratory, in a go/no-go and habituation/dishabituation paradigm. The implementation of physiological measurement protocols would finally provide accurate measurements and would best investigate the question of information coding in crocodiles.