Cats purr in a variety of situations and there are a number of theories as to why they do it. It could even be therapeutic.
Why Do Cats Purr?
The fascinating thing about purring is that cats will do it when they are feeding their kittens, to communicate with other cats, when being patted and when relaxed, but they will also purr when in distress. Cats who have suffered trauma such as being hit by a car, or are at the vet clinic will often purr, despite being obviously in pain or discomfort. Purring is found in Felids and also Genets, but no other species. Kittens will purr at only a few days old.
What Does Purring Mean?
In some cases cats purr because they want to be fed and many cats have essentially trained their owners that this noise means they should hop to it and get that food bowl filled. They also purr to communicate with their kittens and kittens can purr while suckling. They may also purr to diffuse confrontations with other cats and to indicate they don’t want to fight. The purr is also theorised to be a form of self-soothing, which might explain why they purr at the vet or while in pain.
How A Purr is Made
When a cat purrs the inspiratory and expiratory phase of breathing is equal. There is no specific purr structure, but it is thought to originate in the larynx and vocal folds. Some lucky scientists have dedicated their careers to analysing the purr of Felids and have found the frequency varies slightly during the inspiratory and expiratory phase. It is frequently quoted as being between 25-150 Hertz.
A wonderful theory about purring is that it could contribute to fracture repair and healing in the cat. The frequency of a purr is in the range that aids healing and maintains bone density. Cats often clock up 18 hours of sleep a day, which doesn’t leave much time for the weight bearing exercise necessary to maintain bone density. Perhaps cats need to be included in the space program, where decreased bone density is a known problem?
Whatever the cause purring has certainly evolved as a form of communication between cat and pet owner. This lovely sound signals contentment when being patted, but also could be a form of self-healing and self-soothing.