You can work out the real reason why domestic cats purr by observing when they do it. There was a time when people believed that the purr simply meant that their cat was contented. But there’s more to it than that. Thanks to the repeated observation of domestic cat behaviour we know that cats purr under a range of different circumstances such as when they are in great pain and injured or in labour and even when dying. You cannot argue that a cat is contented when dying. Therefore we have to come up with a different reason as to why cats purr.
Purring is heard under a variety of conditions
- When kittens are sucking at the nipple. This is to tell their mother that they are well. She will reciprocate and purr to them to tell them that she, too, is relaxed and in a good state.
- When a mother is lying down with kittens. She does this to reassure them.
- When a mother approaches her nest where the kittens are hiding. This is to tell her kittens that there is nothing to fear by her approach.
- When a young cat approaches another to play. This is to signal to the other that they are in a relaxed mood and are accepting of their subordinate position
- When an adult, dominant cat approaches another who is in a subordinate position in order to send a signal that their intention is non-hostile.
- Conversely, when an inferior or subordinate cat approaches a more dominant cat as an attempt to appease and to send a non-hostile signal.
- When an injured or sick cat is approached by a dominant one to let the dominant cat know that they are in a week non-hostile mood.
- When a cat is in fear and/or in pain and injured and near their human guardian.
- When a cat is contented on your lap or in a similarly contented position close to you.
These circumstances indicate to us that purring is a sign of friendship. It is a vocalisation which occurs when a cat is contented and with a friend or when the cat NEEDS a friend i.e. when they are in trouble as for example when they are about to be euthanised in a veterinary clinic.
Dr Desmond Morris, who is the greatest cat behaviourist, describes it very succinctly by saying that “the nearest human equivalent of purring is smiling”. People smile when they want to send a signal to another that is non-hostile, reassuring and sometimes submissive and appeasing. Also people smile when they are content and happy.
He says that the key message under many circumstances of the smile and therefore of the purr is “I’m not going to do you any harm”. The smile lowers tensions and softens the interaction between humans. It oils the works and makes human interaction more successful. The same goes for cats.
Wild cat species-the tiger
I have to mention the tiger as an example of a wild cat species that can’t purr. Some wild cat species do purr such as the puma. Of course, domestic cats can’t roar as the tiger can but the tiger does have some close range vocalisations which substitute the domestic cat’s purr. These vocalisations function in a similar way to the purr for greeting, reassurance and appeasement. The friendly sounds made by the tiger include the prusten and grunts. The prusten is a staccato puffing sound audible only at close range. It is part of the tiger’s overall greeting behaviour. The sound is created by exhaling air through the mouth and nostrils which makes the lips flutter. It is a friendly or non-aggressive sound like the purr.
Interestingly, tigresses use the prusten to communicate with their young to maintain contact with them. This reflects the purr delivered by the domestic cat mother to her kittens as mentioned above.
How the purr sound is made
In 1992, Dr Morris speculated in his book Cat World as to how the purr was made. In 2020 Wikipedia says that the cat purr is still an object of speculation with different theories proposed. So we don’t know for sure how the purr is made. Dr Morris decided that the purr is a bit like noisy breathing made by humans when they are asleep i.e. when they are snoring. The sound is created because of a second pair of chords in addition to the normal vocal cords in the cat’s voice box or larynx. With every inhalation and exhalation air passes over the “false vocal cords” which makes the rrrrrr sound of the well-known purr. About 30 times a second the laryngeal muscles must contract to interrupt the airflow.
Some more on cat sounds
Purring is caused by a simple airflow over connective tissue masses embedded in the vocal fold of the larynx
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