Still today, many people believe purring is solely a sign of love and contentment. It is but it is also more than that and its purpose is more flexible and subtle. We know a lot more about purring today than we did several years ago but there are still some gaps in knowledge. I hope this page adds some more information. The more we know and understand the better we can be at cat guardianship.
When and why
Purring is gentle and quiet; designed to be received by a cat or person who is close by. It is thought to have evolved as a signal produced by kittens and not adults. For the domestic cat’s wild ancestor, the only times close range communication that takes place is (a) at mating and (b) vocalizations between kitten and mother. We know kittens purr when suckling. The mother may join in. It is a reassuring mutual communication. When the kittens are more adult and the mother wants them to start on solids, kittens often request milk by purring. The purr is a request, in this instance.
Cats don’t only purr when in physical contact. We know our cat purrs when walking around requesting food from us and/or acknowledging that it is about to be delivered. When the purr is a request it may take on an urgent quality in order to get the attention of the owner. This sort of purr may have developed because of the cat’s relationship with humans. This special purr with baby cry undertones may tweak maternal instincts in the person and is used to request food from their caretaker. In a different settling, purring may continue when the cat is angry.
Cats also purr when greeting another cat (or person) they are friendly with. Purring also occurs when cats are engaged in mutual grooming or simply in contact with another cat. Cats can purr when distressed, anxious (‘stress purr’), after being injured and shortly before death. Although the purr is used in many situations it most often used when the cat is happy and wishes that contentment to continue (a signal requesting it).
The situations under which purring occurs indicates that it is a signal and close range vocalization which says,
- “please settle down next to me”.
- or it is saying “I need friendship”.
- or it is a thank you for friendship.
- or a request for food or to continue something enjoyed such as being stroked.
- or a request to change a situation to the cat’s advantage. The cat has learned that purring can make life better in the human/cat relationship.
Bradshaw believes that purring is a request asking either a cat or the human guardian to do something. So, for example, when a kitten purrs to his mother while suckling he is requesting that she lies still while he feeds. The wildcat kitten cannot guarantee she’ll comply because she may have to hunt to feed herself.
In general adult cat-to-cat purring communication, it is believed that purring is a request to stay still. Bradshaw says he has seen his cat Libby purring while grooming her mother and simultaneously placing a paw over her mother to physically keep her still.
Purring is said to have healing properties (e.g. improve bone density). It is said that purring is infrasonic (low-frequency sound). Infrasound can travel through objects. However this is probably incorrect as purring has a frequency of 27-44 Hz and low-frequency sound is classified as below 20 Hz. There is a lot on the internet about the healing powers of the purr but I don’t believe that, as yet, it has been scientifically supported. However. Sarah Hartwell of Messybeast says that the therapeutic frequency range is 20 Hz to 200 Hz. The most healing frequencies are 25-50 Hz. She says that she likes to believe that the purring of her cat Kitty III helped her recovery from a shoulder muscle injury. Sarah believes that purring has a wider use that mere communication; hence her belief that it has healing powers.
How the purr is produced
Purring is almost continuous and emanates from the area of the voicebox. It is created when both breathing in and out. The sound changes between inbreath and outbreath. It almost stops on the changeover. The inbreath purrs are shorter and louder while the outbreath purrs are longer.
The purr is a bit like a low-pitched hum. The vocal cords are vibrated by a certain set of muscles – the laryngeal and diaphragmatic muscles which are sent intermittent signals from the brain. For a hum the sound is produced by air passing over the vocal cords so they vibrate but for the purr the vocal cords “bang together”. Sometimes a cat will hum simultaneously on the outbreaths. The hum and purr together makes the purring more rhythmical.
Music designed for cats has come on leaps and bounds. One track called Cosmo’s Air has a tempo of 1380 beats per minute and is related to purring. More coming up shortly on cat music.
The reference to Bradshaw is a reference to John Bradshaw PhD in his book: Cat Sense….