The order of the Testudines includes all species of aquatic and terrestrial turtles. They are vertebrate animals easily recognizable by their characteristic shell, a modified rib cage that is also part of their spinal column.
For a long time it was thought that turtles were mute, however, it is now known that they have a complex communication system, which even develops before hatching from the egg. Given this new evidence, it is time to ask if turtles listen to and how. We explain it in this article on our site.
Turtle auditory system
Turtles, unlike other vertebrates, have no external ear, that is, they lack ears. However, this does not mean that they do not have an auditory system, since they do have a middle ear and an inner ear Inside it is located thetympanum , which is surrounded by the bony labyrinth, unlike what happens in other reptiles, which has a covering of scales.
On the animal's head you can see, on both sides, behind the eyes and just in the final fold of the mouth, two membraneswith a rounded shape and pearly color, whose function is to protect the middle ear from any damage from the outside.
One aspect to highlight is that the middle ear is made up of a single bone and that it connects to the oral cavity. Its function is the transduction or transformation of the sound captured by the animal. Due to the auditory anatomy of turtles, they often suffer from ear infections or otitis
As for the inner ear, it is where the sound is received already inside the head, but it also intervenes in detecting the position of the body and, also, in perceiving the acceleration that the animal makes when it mobilizes. Regarding its conformation, it is made up of several structures that are embedded in the bone and that are also covered with nervous tissue.
Are turtles deaf?
Turtles are not deaf, on the contrary they are capable of hearing low-frequency sounds, some even imperceptible to people and other animals. In addition, some studies[1] have reported that turtles are capable of producing various types of vocalizations, which can be like shrieks, crackles, low or guttural whistles or harmonic sounds, all of them in different frequency ranges.
Taking these data into account, it can be considered that the communication system of these animals is complex and there are even species in which up to 17 different types of vocalizations have been identified. For this reason it is not possible that the turtles are deaf, since the various sounds they produce have a communicative intention Examples include courtship or the relationship of the young each other and with their mother, even while inside the egg.
In relation to this last aspect, it has been verified that the hatching of the egg in certain species of turtles occurs in a synchronized way, for which they use the emission of sounds to communicate, so that they begin to emerge in groups to go to the water en masse and thus reduce the chances of predation, which increase if the transfer is done individually.
Groups of females have also been observed in the water, near the spawning site, whose purpose is to emit sounds that serve as a guide for the newly hatched turtles to meet their mother. In any case, it is important to mention that more studies are still needed to clearly understand the sounds that turtles make and for what purpose.
How do turtles hear?
Turtles are able to hear better under water than out of it, which is an advantage for species that live in aquatic media. This is due to changes in the large, air-filled middle ear and the tympanic disc.
Optimal sound pickup underwater is possible because the eardrum is able to vibrate at fairly high frequencies, and in addition, the middle ear can fill a little with water, which allows strong vibrations to be dampened. The hearing capacity of these animals is focused mainly on low frequencies, especially in marine species, more than in terrestrial ones.
The communication system of turtles has been interfered, in recent times, by the considerable increase in marine noise caused by human activities, especially related to the use of boats. Affecting the perception of the sound of these animals can produce negative impacts on their lives, for example in their reproduction process.
