The idea of reptiles hearing may seem unusual, particularly for snakes, which lack external ear structures. This often leads to the belief that reptiles are deaf or have only limited hearing. However, reptiles do perceive sounds and vibrations. Their auditory systems, different from mammals, are adapted to their specific environments, showing diverse ways they detect and interpret sound.
How Reptiles Hear
The general reptilian auditory system includes an inner ear, a middle ear cavity, and often a tympanum (eardrum). Sound waves cause the tympanum to vibrate, transmitting these vibrations to a single middle ear bone called the stapes or columella. The stapes fits into an opening in the skull, leading to the inner ear.
The inner ear contains parts like the semicircular canals for balance, and the utriculus, sacculus, and lagena, with the lagena being the primary site for hearing. Inside these fluid-filled structures, vibrations activate sensory cells in the cochlear duct, sending signals along the auditory nerve to the brain for sound interpretation. While many reptiles have a tympanum, some species, especially those underground, may have it covered by scales or lack it. These species rely on low-frequency ground vibrations, detected by the quadrate bone connected to the lower jaw, which transmits vibrations to the extrastapes and stapes, reaching the inner ear.
Hearing Across Reptile Groups
Auditory mechanisms vary across reptile groups, reflecting their diverse lifestyles and environments.
Snakes
Snakes do not have external ear openings or eardrums. They primarily detect vibrations through their jawbone and skull, transmitting these sensations directly to their inner ear. Snakes can also perceive airborne sounds, particularly in the low-frequency range of 50 to 1,000 Hertz, with peak sensitivity around 80 to 300 Hertz, depending on the species.
Lizards
Lizards have visible ear openings and eardrums, allowing them to hear a broader range of airborne sounds than snakes. Their hearing is sensitive within the 500 to 4,000 Hertz range, with peak sensitivity around 700 Hertz for species like the green iguana. Some lizards, like geckos, have sensitive hearing, extending up to 10,000 Hertz. They can also use their saccule to detect very low-frequency vibrations (50 to 200 Hz) from the ground.
Turtles
Turtles have reduced external ear structures, with their tympanum often covered by facial tissue. Their hearing relies on bone conduction, where sound vibrations travel through their shell and bones to reach the inner ear. Sea turtles are adapted for underwater hearing, with fatty tissue under the tympanum aiding sound transmission. They are most sensitive to frequencies between 200 and 700 Hertz.
Crocodilians
Crocodilians have developed ear structures, including movable ear flaps that can seal the ear opening when submerged. These flaps protect the inner ear and allow them to hear effectively both above and below water. Crocodilians hear well, responding to low-frequency sounds in the 50 to 1,500 Hertz range. Their inner ear structures aid in sound localization.
The Importance of Hearing for Reptiles
Hearing plays an important role in the daily lives of reptiles, aiding them in various survival behaviors. Many reptiles use hearing to detect prey, such as sensing the movements of small mammals or insects. This allows predators to pinpoint potential meals even when vision is limited.
Hearing also serves as a defense mechanism, helping reptiles avoid predators by detecting approaching threats through ground vibrations or airborne sounds. This early warning system provides time for the reptile to seek cover or prepare a defensive response. Some reptile groups, particularly crocodilians and certain lizards, use vocalizations for intraspecies communication, including mating calls, territorial displays, and distress calls in juveniles. This acoustic communication helps in social interactions and maintaining group cohesion. Hearing also contributes to their navigation, allowing them to orient themselves by perceiving sounds and vibrations.