Cat purr

This fine picture came up searching for "cat purr" - they must be purring - photo by isazappy (CC)

We as humans should learn to purr to our cats. A cat purr is motivated by contentment, isn't it? We all know that when we stroke a cat she/he purrs because she is content. But it is not as straightforward as that because cats also purr when in pain and injured. You'll rarely be around to notice but you'll hear a cat purr when a cat is in labour or even when near death.


What is a cat purr and why does it happen?

It seems that the trigger for it is when the cat is asking for friendship (a form of request) or receiving friendship (a form of thank you).

A kitten first uses this form of communication when she is suckling on her mother, drinking milk. The kitten will purr while drinking which tells the mother she is receiving milk while the mother will purr in return to tell her kittens all is well her end.

Purring can be performed with the mouth shut and in a two way motion, meaning when inhaling and exhaling (and also when drinking). Pretty amazing really.

Big cats such as the Cheetah (the smallest of the big cats) and the Bengal Tiger (the most common tiger but still dangerously close to extinction) cannot purr two ways and their one way exhalation purr is less accomplished. They can roar though and I've never heard my cat roar....! So it's evens between the big and little cats in respect of their communication abilities.

Sometimes the purr is very quiet. I can check if my cat is purring by gently placing my fingers on her throat to feel the vibrations. This is a way of communicating with my cat as I'll know she is content and she'll tell me she is content.


Photo by kcl_seattle under creative commons license. We use the warm cat's purr to give the impression a place is comfortable, cosy and content.


The next question is how is a cat's purr produced?

These are my thoughts: The sound is obviously produced deep inside the cats body as her whole body can vibrate. For me it originates near the vocal cords, throat, neck area. Air from breathing is passed over a piece of anatomy that vibrates in much the same way a singers voice produces a vibrato on the long notes. The purr though is not produced by the vocal cords and as it emanates from the area of the vocal cords it must be another piece of anatomy in the air passages in the throat (leading to the lungs) that vibrate.

What do the experts say? A cat's purr has a frequency between 22.4 - 30.2 hertz. The experts are not sure how the sound is produced but it probably emanates from the larynx, an area of the throat that houses the vocal cords. It is thought that the muscles of the larynx are constricted and relaxed in quick succession.

A cat purr has good harmonics apparently. A harmonic is one of a number of component frequencies (sounds) of the main sound produced (that is my layperson's interpretation of the word harmonics - if I am wrong please tell me in a comment if you have time).

So, the purr is quite a complex process and it sounds really nice too.

Source: Wikipedia, Myself.

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