Naïs CARON DELBOSC : Multimodal perception of aerial sounds and aquatic vibrations in crocodiles

From 01/10/2021 to 30/09/2024

Laboratories : CRNL CAP - ENES Thesis director : Nicolas Mathevon (ENES) et Nicolas Grimault (CAP)

Summary :
As top predators, crocodilians are very well equipped to probe their environment: excellent vision at least in air, highly developed smell, extraordinary abilities of mechano-reception, and an acute sense of hearing. We have recently studied how crocodiles locate the position of an airborne sound source, and how these animals identify airborne acoustic signals in their noisy environment thanks to their ability to categorize sounds along a sound continuum. During this PhD project, we will integrate a new perceptual dimension of crocodiles: aquatic vibrations. Crocodiles lead an amphibious life, at the interface between water and air. Their ears are mainly dedicated to the perception of airborne sound waves, while mechanoreceptors distributed on the body of the animal and especially all around the mouth are sensitive to aquatic vibrations. The objective of this project will be to understand how the crocodile integrates information from these two sensory channels. Through propagation measurements, we will evaluate the information transmitted to a swimming crocodile at the air-water interface by airborne sound waves and aquatic vibrations in naturalistic situations (e.g. when a prey approaches the water body and starts to drink). We will then test through playback experiments in the wild and in the laboratory (using loudspeakers and vibratory devices), how crocodiles integrate information from these two channels. We will test the following hypotheses: 1) do water vibrations produced by the prey add information to the airborne sound signals, and allow the crocodile to identify more precisely the cause of the sounds and vibrations (i.e. size of the prey; appropriate moment to approach it), 2) do water vibrations increase the reliability of the information provided by the airborne sound signals, by improving for example the crocodile's ability to localize the source. We will also evaluate the ability of crocodiles to combine the information provided by airborne sounds and waterborne vibrations spatially (co-located or separate signals) and temporally (signals arriving simultaneously or successively).