Cats and Their Irresistible Purring

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How, physically, do cats purr? Why does it sound so sweet and melt our heart? Image by Fleshgrinder.

All cat-lovers recognize the familiar purring sound that their feline friends make. This is usually seen as a sign of contentment, but there are actually many other situations where a cat may purr which are far more indicative of what functions this ability may have.

Cats Purr For Self-Healing and Comfort

Cats often purr while in pain or anxious, such as during injury or a trip to the vet, leading researchers to conclude that this unique type of vocalization may be a method of self-healing. It turns out that purring releases endorphins, soothing and relaxing the animal during conditions of stress.

It’s common for female cats to purr while they’re giving birth and continue to do so as the kittens start to nurse. In fact, this is such an important way to communicate between mothers and their young that kittens learn to purr within days.

As bizarre as it may seem, researchers have suggested that purring developed to allow our domesticated tigers to spend all day snoozing in the sun, avoiding any form of strenuous exercise. In theory, a cat’s purr  – with a frequency of around 25 Hertz, which happens to be the frequency at which bones heal more effectively – can offset any potential loss of bone density due to the lack of activity.

Dr Robert Eklund, speech technologist and big cat specialist from Linköping University, Sweden, is of the opinion that purring “could have something to do with it, but this has never been tested.” Nevertheless, it is appealing to speculate that purring grants our tabby companions a speedier recovery from illness. Everybody is familiar with the notion that cats have “nine lives;” wouldn’t it be interesting if purring provided the scientific basis for this feline mythology?

What is Purring, Really?

No one really knows exactly how purring is produced,” Dr Eklund told Decoded Science. At best, researchers know that it involves a repetitive signal from the brain to the diaphragmatic and laryngeal muscles – commonly known as the voice box – causing the muscles to twitch at a rate of about 25 vibrations per second (hence the 25 Hertz as described above).

This causes the vocal cords to open and rapidly close, creating the familiar purring sound. Crucially, these muscles can work both during inhaling and exhaling, giving the impression that the cat is purring constantly. This is different from a “meow,” which only happens when the animal exhales.

Domesticated Cats Aren’t the Only Ones Who Purr

Domestic cats aren’t the only ones with this ability. Wild cats – such as bobcat, lynx, puma and cheetah – can also purr, which Dr Eklund has had a chance to record.

However, not all big cats can purr and an important distinction has been made between purring and roaring: Cats that purr can’t roar, and cats that roar can’t purr.

This subdivision was originally made based on a slight difference in the hyoid anatomy. Animals with an incompletely ossified bone were classed as “roaring cats,” whereas animals with a completely ossified hyoid were considered “purring cats.”  Researchers no longer accept this definition, and now believe that purring vs roaring is a consequence of specific characteristics of the vocal folds and vocal tract.

When Asking For Food, Cats Can be Very Purr-suasive

It seems that domestic cats may also use their purring powers to communicate with their owners. Researchers from the University of Sussex, UK, led by Dr Karen McComb, found that camouflaged within the normal low pitch purring, cats can include a high pitch sound that seems to give gullible owners a sudden urge to feed their devious pet. Dr McComb suggested that this type of purring is more acceptable to humans than meowing, which is far more likely to get cats thrown out of the bedroom when asking for food before the alarm clock goes off.  Curiously, even people with no experience in dealing with cats described this type of purr as needing urgent attention.

The team examined purring from 10 cats and measured an unusually high peak between 220 and 550 Hertz. They suggested that this appeals to the human nature to respond to cry-like sounds – a baby’s cry achieves a similar frequency range between 300 and 600 Hertz. Dr McComb suggested “the inclusion of this high frequency element within the purr could serve as a subtle means of exploitation, tapping into an inherent sensitivity that humans have to nurturing offspring.” Quite a neat trick to ask for food!

Why Do Cats Purr?

Whether wild or domestic, cats purr for a variety of reasons. Next time your housecat comes to you with a persuasive purr, pay attention, he may not just be telling you he’s happy!

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