Why, and how, do Cats purr?

Cheetah and Cub by Steven Tan, on FlickrKitty is great at telling you when she’s happy. When stroking her, tending to her needs and sometimes even when she is around other animals, she vocalises her feelings in the same way: she purrs. It’s a low, buzzing sound that once you hear it, may mean that your cat is happy. Or it could mean that she is sad, she wants attention or wishes to be left alone. It’s a truly mysterious way to communicate… in more ways than one.

The fact is, there is no definite explanation for how or why cats purr – cats have no unique anatomical features that are responsible for the purring sound (they have no ‘purr box’). However, scientists have generally agreed that the larynx (voice box), laryngeal muscles, as well as a ‘neural oscillator’ (a set of nerves that send rhythmic/repetitive signals) are involved – notably, domestic cats with paralysed laryngeal muscles, for example, do not possess the ability to purr.

And it’s not just domestic cats that purr. The sound is present in other species within the cat (Felidae) family, from pumas to cheetahs, to wild cats and lynxes (it’s quite scary to think of a lynx purring!). The felines’ relatives also purr, such as civets, mongooses and even raccoons, hyenas and guinea pigs.

However, what makes the purr different to other noises produced in the animal kingdom is that it is produced during the entire breathing cycle; whereas other vocalizations such as a cat’s “meow” are limited to the expiration of the breath. Strangely enough, cats that purr can’t roar (and vice versa) because the tissue surrounding roaring cats’ larynxes are too soft to allow purring (so be very shocked if you hear your local tiger or leopard purring!)

Despite the lack of scientific evidence to prove how and why cats purr, some theories suggest the behaviour is an evolutionary one stemming from kitten-hood: as the mother returns home, she will quietly signal (i.e. purr) to check that all is OK while avoiding attracting attention from predators. In response, the kittens will suckle and purr at the same time. Moreover, a cat will continue to purr into adulthood – there have been suggestions that not only does the cat purr as part of a bonding mechanism, but also from contentment and pleasure (think about the amount of time spent stroking and tickling your pet cat, longing to hear that low, purring sound!) as well as alerting you of injury or in pain.

Bizarrely, some have suggested that cats purr to strengthen their bones and muscles – the vibrations stimulating their skeleton to thicken. A bit like a vibrating exercise plate, a purr runs at between 25 and 100 vibrations per minute – a rate that seems to be the right to give puss something of a vibro-workout.

Happy, sad, or just in need of a workout, it’s actually trickier to know what your pet is really thinking.

 

Image Source: Cheetah and Cub by Steven Tan, on Flickr

Article by Chloe Westley

September 9, 2014

Based in Manchester, UK, Chloe spends most of her time getting up close and personal with a zippy bit of kit called a Raman spectrometer. In between doing some high-brow research as part of a PhD, she follows tennis, cricket and Man United (unfortunately) and loves watching Suits, The Big Bang theory and Breaking Bad (obviously!).


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