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Word of the Week: The One with a Tympanum

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Welcome to Word of the Week! Every Friday here on the High Park Nature Centre blog we will teach you a new word to amp up your nature vocabulary! This week, the word that you will be learning about is Tympanum!

What Does Tympanum Mean? 

Tympanum [TIM-puh-nuh m](noun): The ear cavity or eardrum that is found in certain animals such as amphibians, reptiles and insects (in amphibians, normally covered by a circular membrane). When making a reference you can say tympanum or tympanum membrane. 

In ancient Greece and Rome, a tympanum was a small hand-held drum, similar to a tambourine. The Greeks version of the word tympanon, from the root, typtien meant to beat or strike. 

Why Do Animals Need a Tympanum Membrane

Which creature in the wetland makes the best drummer? Ba-dum-bum… The one with a tympanum! 

Amphibians like frogs, some reptiles and many insects use this protective circular patch of skin stretched over a ring of cartilage (just like a drum) to transmit sound waves to the middle and inner ear for interpretation by the brain. 

The transmission of these sound waves helps them sense prey, know where their predators are, find potential mates, and locate where potential rivals are by hearing the intentional and unintentional sounds they make! 

In insects, depending on the species, the tympanal organ will be located in a different area. In reptiles, the tympanum is located at the back of the head. What a very cool and important tool!

When trying to interpret sound waves, lizards, for example, can hear the best when a sound is between 400 and 1500 hertz! Which means they can hear best from sounds such as birds to the oboe! 

In these animals, the tympanum is usually the top of the head or the end of a short open tube that might be covered in scales.  

Crocodiles have keen hearing abilities. They have an ear on the outside that is made from a short tube that is closed by a valve flap, which leads to the tympanum. The American alligator can hear sounds that range between 50 hertz such as the hum of an AC and 4,000 hertz such as a cymbal. 

Crocodiles use their hearing not only to know where their prey and their competitors are but also in their social behaviour. Males will roar to either threaten other males or to attract females! 

The hearing or turtles though are not as strong as crocodiles are still pretty good. Furthermore, they also have a large tympanum. 

Research showed that in some species of turtles, the inner ear is sensitive to airborne sounds that range between 50 hertz such as the hum of an AC to 2,000 hertz such as glass breaking. 

Snakes, though they are reptiles, don’t have a tympanum. When it comes to their hearing, they are more sensitive to the vibrations on the ground than to airborne sounds. If you make a loud noise in the air and you don’t move the snake will not move. 

However, if the ground is tapped or scratched, then the snake will raise its head and flick in and out quickly. The snake will hear when the vibrations of the noise travel through the quadrate bone that is in its lower jaw.

For a frog, the tympanum allows it to hear both in the air and below the water. Don’t be fooled, this lack of an outer ear belies a very exciting internal relationship between the sound the frog makes and the sound it hears. In some species of frog, the size of the tympanum as well as the distance between its two eardrum membranes is relative to the frequency and wavelength of the species’ male call. To create this call, the lungs produce an air pocket in the vocal sac emitting sound that can be heard from kilometres away! You might wonder how the frog can handle hearing such a loud sound!

The interconnected air route between the tympanum and the lungs protects the frog from damage to the eardrum since the air pressure coming from inside the frog’s body is dampened by the tightly pulled membrane of the tympanum.

Let’s take a look at another critter that is closer to home: the grasshopper! The hearing organ in grasshoppers is located on both sides of the first part of the abdomen near the base of the hind leg. Though the most common way for insects to hear is through the tympanum, some will hear through echolocation or through the vibration of tiny hairs on their skin. 

When grasshoppers receive sound waves, they will use both the external tympanum and the internal chambers, allowing them to hear. This process is so advanced that they can detect the direction of the sound almost as well as humans.

Sound communication in grasshoppers is mainly used for mating purposes. The male will start the call, usually with a whirring or snapping noise, then he will listen for a response. Because grasshoppers are sensitive to hearing, he can tell where a female is. 

If you are walking near one of the ponds in High Park in the coming weeks, you may hear a sound reminiscent of a rubber band being snapped or a banjo string being plucked. If you try to imitate it, I wonder if you’ll get a response?!

At the High Park Nature Centre, our guides teach visitors how to be more aware of the environment around them every day! On your next family trip or a weekend with friends, plan a trip through one of our guided nature hikes

Learn more about frogs, and other animals in their natural habitats here at High Park Nature Centre!     

References:
http://online-field-guide.com/glossary.htm#Anatomy%20-%20T
https://www.burkemuseum.org/collections-and-research/biology/herpetology/all-about-amphibians/all-about-frogs
https://animals.mom.me/sensory-organs-found-frogs-head-3278.html
https://acoustics.org/pressroom/httpdocs/swa9501.html
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