Why Do Cats Purr?
Most people think that cats purr to show pleasure or contentment. Purring is a kind of low continuous rattling hum, but it has nothing to do with a cat’s real voice, for the vibration frequency is far lower than that of the vocal chords. In fact, a mother cat uses purring to call her kittens to feed.
At birth kittens cannot see, hear or smell but they can feel the purring of their mother as a vibratory movement and so come towards it to nurse. Once the kittens are feeding, the mother stops purring. So it would seem that purring began as a kind of homing device and your cat may simply be reminding you that he is there so that you will continue to stroke him.
Purring may have developed as an evolutionary advantage as a signaling mechanism of reassurance between mother cats and nursing kittens. Post-nursing cats often purr as a sign of contentment: when being petted, becoming relaxed, or eating. Some purring may be a signal to another animal that the “purrer” is not posing a threat.
Purring sometimes seems to be a way for cats to signal their caretaker for food. This purring has a high-frequency component not present in other purrs. This variety of purring seems to be found only in cats in a one-to-one relationship with a caretaker. Cats often purr when distressed or in pain, such as in labour. This purring may trigger a cat’s brain to release a hormone which helps it in relaxing and acts as a painkiller.
Purring may also be a healing mechanism to offset long periods of rest and sleep that would otherwise contribute to a loss of bone density. The vibrations and contractions of a purr show a consistent pattern and frequency around 25 Hz; these frequencies have been shown to improve bone density and promote healing in animal models and humans.