Why do cats purr?
Is a purring cat really a happy cat?
Unlike our domestic moggies, adult cats that live in the wild rarely purr at all. In fact, it is only kittens that purr to their mothers. Amazingly, through the process of domestication and human contact, cats retain this infantile trait to call to their owners – us. Cats, it seems, have a kind of language that they use exclusively with us and it turns out that there is actually more than one type of purr.
Every morning Dr Karen McComb from the University of Sussex was being rudely awakened by her cat Pepo and wondered why the purring she could hear was so difficult to ignore. This led Karen and her team to ask a group of volunteers to rate different purrs based on how urgent and pleasant they perceived them to be.
Unlike the purr that cats produce when curled up on your lap, the team discovered a distinct purr that incorporates a shrill frequency, similar to that of a baby's cry. This embedded frequency in the 'solicitation purr' is produced when cats are seeking attention or food. Through evolution, we have developed a 'sensory bias' to higher pitched 'baby-crying' sounds and cats seem to have exploited this.
When the team played the recordings back to human volunteers, even those people with no experience of cats found the soliciting purrs more urgent and less pleasant. The scientists were also able to remove the cry acoustically and show that the purr lost its urgency.
