There is a misconception that you must possess flappy ears for auditory perception. Is it possible to hear without ears? Today, let’s see how turtles hear when they have no ears. We wonder how these animals hear without those external ears fluttering, as seen in dogs or elephants.
Technically, turtles do not have ears but are not deaf – they have internal ears.
Understanding hearing
The outer ear channels external sounds to the middle ear, where the eardrum and auditory bones amplify the sound waves. The inner ear is the last stop for the sound waves, where they are converted to electrical impulses to transmit the signal to the brain center through the auditory nerves.
Hearing like a turtle
For turtles, hearing is a secondary sense and is compensated by primary senses, such as vision and smell. Hence, the auditory center in the brain is relatively small compared to the brain centers of other senses.
Turtles do not have external ears, nor do they have eardrums. They have thin flaps over the skin, through which they receive vibrations and low-frequency sound waves that enter from the sides of their head. The internal ear receives both the vibrations and low-frequency sounds and amplifies them. The internal ear also bears auditory nerves, which convert the sound waves to electrical impulses, which are further transmitted to the brain center for interpretation.
Can turtles hear what we hear?
Turtles can hear sound waves with frequencies between 50–1000 Hz, while humans can hear between 20 Hz to 20,000 Hz. So, turtles cannot hear everything we hear.
Turtles cannot hear the higher-frequency chirping of birds, but they can hear birds’ wings flapping. Turtle hearing is limited to the detection of vibrations and low-frequency sounds. Their ears help detect changes in water pressure that might indicate a predator is nearby.
Adaptation to aquatic life
Research shows that turtles possess large inner ears to adapt to aquatic lifestyle, and visual sensitivity. They also have larger bony labyrinths in the inner ear, much larger than that found in some mammals. The large labyrinths help turtles adapt to aquatic habitats.
An evolved ear to hear underwater
Turtles and tortoises can hear better underwater than on land. A study published by Kate Willis has a plausible explanation. These species have large, air-filled sacs inside the skull, which vibrates more strongly under water as sound waves travel faster in water.
Turtles have peculiar ears – a non-existent outer ear, a poorly formed middle ear, and an abnormally over-sized inner ear. The large inner ears help in eye stabilization under water.
Conclusion
Turtles do not have external ears but have modified internal ears that help in hearing low-frequency sounds and vibrations. It is incredible how turtles have evolved to adapt to marine, freshwater, and terrestrial life.
References
1. How the Ear Works, Health, John Hopkins Medicine.
2. Willis, K. L. (2016). Underwater hearing in turtles. In Advances in experimental medicine and biology (pp. 1229–1235).
https://doi.org/10.1007/978-1-4939-2981-8_154
3. Willis, K. L., & Carr, C. E. (2017). A circuit for detecting interaural time differences in the nucleus laminaris of turtles. The Journal of Experimental Biology, 220(Pt 22), 4270–4281. https://doi.org/10.1242/jeb.164145
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