Hearing with an atympanic ear: good vibration and poor sound-pressure detection in the royal python, Python regius.

Area of Science:

• Zoology
• Bioacoustics
• Sensory Ecology

Background:

• Snakes lack external and tympanic middle ears, structures crucial for airborne sound pressure hearing in most tetrapods.
• This anatomical difference suggests snakes should have poor pressure hearing but acute sensitivity to substrate vibrations.

Purpose of the Study:

• To test if snakes (specifically royal pythons) are sensitive to sound pressure.
• To investigate if their sensitivity to sound pressure is due to direct pressure detection or substrate vibrations.
• To quantify vibration and sound pressure sensitivities in royal pythons.

Main Methods:

• Brainstem evoked potentials were measured in 11 royal pythons to quantify vibration and sound pressure sensitivities.
• Vibrograms and audiograms were generated to determine frequency-specific sensitivities.
• Three-dimensional head vibrations were measured in response to sound pressure at threshold levels.

Main Results:

• Royal pythons exhibited greatest sensitivity at low frequencies (80-160 Hz).
• Sensitivity to vibrations was -54 dB re. 1 m s(-2), and to sound pressure was 78 dB re. 20 μPa.
• Sound pressure at threshold levels induced head vibrations equal to or greater than those induced by threshold vibrations, indicating vibration-based detection.

Conclusions:

• Snakes have lost effective pressure hearing due to the reduction of their outer and middle ears.
• Snakes possess acute vibration sensitivity, which likely accounts for their perception of sound pressure via head vibrations.
• This vibration sensitivity may play a crucial role in snake communication, predator detection, and prey localization.