The purring cat. It may well be considered the epitome of contentment. But there’s much more to purring than meets the ear.
Research is starting to shed some light on purring -- starting with how cats do it.
How do cats purr? Experts have offered a number of theories over the years. Most now say that purring begins in the brain.
A rhythmic, repetitive neural oscillator sends messages to the laryngeal muscles, causing them to twitch at the rate of 25 to 150 vibrations per second (Hz). This causes a sudden separation of the vocal cords, during both inhalation and exhalation - the unique feline vibrato.
“Opera singing for cats,” is what animal behaviorist Karen L. Overall, VMD, PhD calls it. But the purr is usually so low-pitched that we tend to feel it as much as hear it.
Purring isn’t the sole domain of domestic cats. Some wild cats and their near relatives - civets, genets, mongooses - also purr. Even hyenas, guinea pigs, and raccoons can purr.
Cats that purr, such as mountain lions and bobcats, can’t roar, however. And cats that roar, such as lions and tigers, can’t purr. The structures surrounding their voice box (larynx) aren’t stiff enough to produce a purr.
But it appears these cats evolved the roar for good reason -- mainly to protect their prides, says Benjamin L. Hart, DVM, PhD, distinguished professor emeritus at the University of California, Davis, School of Veterinary Medicine.
“If you’re a big cat and you have to move around a lot to get prey, loud roaring plays a huge part in maintaining your territory,” Hart says.
But small cats are loners and don’t compete with each other for meals, Hart says. Their communication doesn’t need to be far-reaching. For them, scent marking does the territorial trick (as some unfortunate cat owners quickly learn).
The Purpose of Purring
If roaring serves an evolutionary purpose, why do cats purr? We humans have long perceived purring as a simple sign of pleasure, in particular, contentment with our company.
Although contentment does appear to produce purring, cats also purr when frightened or threatened. One way to think about this is to equate purring with smiling, says Kelly Morgan, DVM, clinical instructor at the Chicago Center for Veterinary medicine of the University of Illinois at Urbana-Champaign College of Veterinary Medicine in Chicago.
“People will smile when they’re nervous, when they want something, and when they’re happy, so perhaps the purr can also be an appeasing gesture,” Morgan says, adding that this is purely speculation.
If you’ve ever wondered why your cat is so hard to ignore each morning, you’ll take a special interest in a recent study conducted by researchers at the University of Sussex in Brighton, U.K.