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Purr...
A cat's purr is one of the most wonderful sounds in this world (up there with only a baby’s laugh in my book), it is part of their repertoire of social communication. But how and why do cats make this endearing sound? In short, cats purr when they are content, frightened, ill, females during birth, and when stressed (possibly for comfort and reassurance). For more info, take a look.
How do cats purr?
When you caress your pet cat, the animal seems to vibrate all over. Scientists first thought that cats might possess a special "purring organ." But none has been found. Then by pressing a microphone against different places on a happy cat's body, researchers discovered that the greatest vibrations originated at the cat's throat, right over its larynx, commonly called the voice box. They correctly guessed that the purring must be coming from the cat's voice box. But then, why can't we purr? After all, human beings have voice boxes too.
More research finally uncovered the answer. The puma, bobcat and your pet puss possess something you don't. Inside each of these cats' brains is a special timer.
This timer can send rhythmic nerve messages -- at 25 electrical pulses per second -- to a particular muscle in the cat's voice box. With the first pulse from the brain's timer, the muscle swings the vocal folds in the larynx together. It almost closes off the air passage through the voice box. With the next pulse, the muscle relaxes. The airway again opens. These opening and closing folds change the airflow through the cat's voice box. The airflow is usually steady as the mountain lion or bobcat inhales and exhales. When the timer's working this steady stream turns into a putt-putt-putt of air through the larynx. 1
Why do cats purr?
Happy Cat:
The most popular theory is that cats purr when they are contented.
Communication between mother and kitten:
Because kittens are born blind and deaf, one theory as to why cats purr is that the mother cat's purring is a physical sensation that the kittens can feel to help them find mom so they can nurse. The kittens begin to purr in response when they are less than a week old. The theory here is that the kittens purr to tell momma cat that they are getting their milk and everything is going okay. Although cats can't meow with their mouths closed, a kitten or cat can purr with her mouth closed, so the kitten can purr and nurse at the same time. 2
To heal bones and organs:
Scientists at the Fauna Communications Research Institute in North Carolina have discovered that our purring is a 'natural healing mechanism' that has helped to inspire the myth that we all have nine lives.
Wounded cats will purr because it helps to heal and strenghten bones and organs. Cats purr at between 27 and 44 hertz (a measure of the number of cycles per second and NOT a car hire firm!), exposure to similar sound frequencies is known to improve bone density in humans. Purring is believed to have a similar effect to ultra-sound treatment on humans. 3
To stimulate bones and muscles:
Because cats have adapted to conserve energy via long periods of rest and sleep, it is possible that purring is a low energy mechanism that stimulates muscles and bones without a lot of energy. 4
Endorphins:
A more recent theory about purring is that it is caused by the release of nature’s own morphine-like substances (endorphins) in the brain. Since endorphins are released under circumstances of pain and pleasure, this would explain the seemingly ambiguous expression of purring. This theory jives with Pederson’s reasoning, that purring is initiated in the brain, and is also compatible with the more mechanical explanations for purring, as endorphins activate one of the main action systems in the brain (so thought is translated into movement). Whatever the explanation for purring, it seems to indicate cats’ contentment and is associated with improvement in their affect at times of stress. 5
Some wild cats purr, too!
Mountain lions and bobcats can make a variety of household cat sounds. Baby mountain lions (also called pumas and cougars) and baby bobcats meow like household kittens. As adults, they growl, hiss and spit when they are displeased. When they are contented, they purr.
Of course a full-grown mountain lion purrs about twenty times louder than that friendly puss who sleeps most of the afternoon at the foot of your bed. Not all kinds of cats can purr. Cats that can roar -- such as tigers, jaguars and African lions -- can not purr. And cats that can purr --such as cougars, bobcats and household tabbies -- can not roar. 6
So, just like everything else a cat does, it purrs when it wants to.
Footnotes:
1- Santa Clara, CA.
2- Pet-tails.com.
3- Cats in Charge.
4- Scientific American.
5- PetPlace.com.
6- Santa Clara, CA.
This article may not be reprinted without permission. © Jessica Huffman .
Last update: January 02, 2003
