The purr of a cat is a familiar sound to many pet owners and often provokes feelings of peace, comfort and contentment. While domestic cats often purr in the company of their human owners, cats also purr when they're away from humans, including in the wild. Not all species of cats can purr, and researchers believe that cats purr for many different reasons.
How Cats Purr
For many years, scientists could not definitively explain how cats generated a purring sound. Research now shows that purring begins with signals from the cat's brain that instruct the laryngeal muscles in the cat's throat to twitch rapidly, at 25 to 150 vibrations per second, causing the vocal cords to separate suddenly on inhale and exhale of breath to produce the vibrato sound of a purr. Purring is different from other feline vocalisation, as it is produced during both inhale and exhale, whereas other sounds are produced only on exhale.
When Cats Purr
Cats purr at many different times. When people think of a purring cat, they probably imagine a calm, comfortable house cat curled up in its owner's lap. Cats often purr to express contentment and affection. However, cats also purr when they're in pain, for example, while delivering kittens or when recovering from an injury. Cats may, at times, purr to other cats, during greetings or even while fighting.
Why Cats Purr
A cat's purr seems to have practical application for communication and physical well-being. A happy house cat purring to its owner is most likely signalling approval and encouraging more of the same behaviour, such as petting or grooming. Many house cats take this a step further by using the positive sound of a purr to provoke their human owners to perform pleasing behaviours, such as feeding. Researchers also believe that the frequency of a cat's purr may promote healing, helping bones and tissues to regenerate. Purring can also have a positive effect on humans, promoting feelings of relaxation and helping to relieve stress.
Which Cats Purr
Domesticated breeds of cats with healthy and properly formed vocal cords are able to purr. Many wildcats, such as bobcats and mountain lions, and near relatives of cats, such as mongooses and raccoons, can also purr. Because of the stiffness of their vocal cords, cats that purr do not roar. Likewise, cats that roar, such as lions and tigers, cannot purr. Researchers believe that due to their solitary nature and tendency to evade predators, smaller cats developed the ability to purr because it is more beneficial to them than the ability to roar.