Purring is the vocal buzzing sound that we hear cats make when we pet them. But why and how do they do this? By experience, we can say that cats purr when they are happy. But they are also seen purring when stressed. Then what is the reason behind this?
Like already mentioned, every cat lover will be able to confirm the fact that cats make a typical sound when they are petted or fed by their owner. Deciphering this action in terms of human behavior makes us easily conclude that it's a way of them telling us that they are happy. Cats often purr when they approach other cats that they seem to be have a friendly disposition towards. This has made some assume that they use purring as a means of communication amongst themselves. However, it's not just when a cat is happy or wants to extend a hand of friendship to other cats, that it purrs. Cats who are injured, ill or frightened, also purr. Cats are also known to purr when they are nearing their end. This gives another angle to the whole thing.
The Healing Effect
The fact that cats purr when they are sick or frightened has made researchers turn their direction of studies towards investigating if it has a soothing effect on cats. Certain findings with this respect also give greater credibility to this theory. Scientists have shown that the frequency of a cat's sound lies between 25 and 150 hz. This is the same frequency that various experiments have shown to improve bone density and promote healing. Is this then the reason behind the old saying that cats have nine lives? Well, on a more serious note, many believe that it is this healing effect that cats are instinctively aware of, that makes them purr when they are ill or injured. Purring also aids them in their adaptation to conserve energy through long periods of sleep and rest. Some even weigh the possibility that this is an energy conserving mechanism used to strengthen their bones and muscles.
A recent theory also suggests that it is caused by the release of endorphins in a cat's brains. This substance is released both during pleasure and pain. This fact can be used to explain why they purr when they are both happy as well as when injured. This theory falls absolutely in place with the conclusion of Pederson's studies that the sound is initiated in the brain, as endorphins are known to activate important action systems in the brain.
It is believed that purring was developed as a mechanism of kittens to tell their mother that they are fine. Kittens knead and purr mostly during nursing. A kitten can't meow and nurse at the same time. It can, however, easily purr and nurse together. The mother replies to her kitten by purring back. This is probably the same instinctive behavior that is carried over by cats even when they have grown up, that we witness when we pet our domestic felines.
How Do Cats Purr?
Now, let us shed some light on how these animals produce the purring sound. Well, when we human beings speak, we don't breathe. But what is amazing about a cat's purr is that the animal can produce the low buzzing sound throughout its entire respiratory cycle of inhalation and exhalation. In fact, a cat can meow only when it is exhaling and not while it is breathing in. Earlier, it was thought that the purring noise was the result of blood flowing through the inferior vena cava. However, recent research suggests that it is the laryngeal muscles that cause the purring noise. These muscles make the glottis open and close, which helps to vibrate the vocal cords. This in turn, results in the purring noise.