Underwater Hearing in Turtles

Abstract

The hearing of turtles is poorly understood compared with the other reptiles. Although the mechanism of transduction of sound into a neural signal via hair cells has been described in detail, the rest of the auditory system is largely a black box. What is known is that turtles have higher hearing thresholds than other reptiles, with best frequencies around 500 Hz. They also have lower underwater hearing thresholds than those in air, owing to resonance of the middle ear cavity. Further studies demonstrated that all families of turtles and tortoises share a common middle ear cavity morphology, with scaling best suited to underwater hearing. This supports an aquatic origin of the group. Because turtles hear best under water, it is important to examine their vulnerability to anthropogenic noise. However, the lack of basic data makes such experiments difficult because only a few species of turtles have published audiograms. There are also almost no behavioral data available (understandable due to training difficulties). Finally, few studies show what kinds of sounds are behaviorally relevant. One notable paper revealed that the Australian snake-necked turtle (Chelodina oblonga) has a vocal repertoire in air, at the interface, and under water. Findings like these suggest that there is more to the turtle aquatic auditory scene than previously thought.