Purrrrrr…..

I love watching my 2 cats, especially when my older cat decides to sneak up on the younger one. She crouches down, her ears held low, the tip of her tail twitching. She stealthily prowls over (hiding behind the furniture, of course), until she is close enough. Then – pounce! – out she leaps. (Of course, my younger cat is very used to this game, so she isn’t often caught unawares!) She also does this to stalk the occasional insect that makes its way into the house. From everything that I’ve seen, a wild cat stalking its prey acts in a very similar fashion. With ears down and crouched low, they slink closer to the target, tail twitching - then they attack.

I love to think about ways in which domesticated cats are like their wild cousins. Stalking prey, cleaning themselves with their tongues, perching in high places to look over their territory, roughhousing with each other – wild and tame cats all do these things. But there’s one thing that tame cats do that I was unfamiliar with in their wild counterparts – purring. My cats purr a lot. But do wild cats do the same? Do lions purr on the African savannah, or tigers when they are relaxing in the jungle? For that matter, what is purring, anyways? And why do housecats do it?

Many people who’ve spent time around cats know that they purr when they are content, such as when they are cuddling on the lap of their favorite person. However, this isn’t the only time that they purr. It also happens when a mother cat is giving birth, when kittens are nursing, or when a cat is severely frightened or injured; cats will even purr as they are dying. An obvious question, therefore, is why?

It is possible that purring serves a mental purpose in cats. For example, a mother cat could be trying to soothe her newborn kittens. The kittens could telling their mother that they are okay. A gravely injured cat could be trying to comfort itself. A stressed cat could be trying to keep itself calm. It is also likely, however, that purring also serves a physiological role, as well. Scientists have shown that the measurable frequency range of a cat’s purr is consistently between 25 and 150 Hertz. This range of sound has been demonstrated to promote physical health, including bone growth and repair, pain relief and decreased inflammation. Apparently there used to be an old adage often repeated in veterinary school – “If you put a cat and a bunch of broken bones in the same room, the bones will heal.” It is highly likely that cats actually purr to help themselves get better – consistent with the observation of purring by injured or dying cats. In fact, here’s something very interesting – comparing cats and dogs, cats heal from injuries such as broken bones or even surgery better, faster, and with fewer complications than dogs.

So that’s what purring does. But how do cats do it? Actually, no one knows for sure. It could be from the hyoid bone, a small flexible bone in the neck. When a cat pushes air through its voicebox, the bone can rattle, possible causing the distinctive rumble of a purr. Alternatively, purring could be caused by false vocal cords, located slightly behind the real vocal cords. Yet another possibility is that it is caused by something called the “neural oscillator” stimulating the vibration of the vocal cords themselves.

This confusion over what makes a cat purr actually makes it difficult to say whether big cats purr or not. I’ve come across multiple references to the purring ability (or lack thereof) of lions, tigers, cheetahs, leopards and jaguars. Here’s what I believe to be the most reliable information. According to a paper published in 2002 in the journal Mammal Review, cats in the Pantherinae subfamily (this includes lions, tigers, leopards and jaguars) can make some snuffling, purr-like sounds as they exhale, but it is not true purring. Only cats in the Felinae subfamily (that is, bobcats, cheetahs, Eurasian lynxes, and pumas) have the ability to truly purr. One possible explanation for this is that Pantherinae cats have a rigid hyoid bone that cannot vibrate as well as the hyoid bone in the Felinae cats.

Don’t feel badly for those lions, tigers, leopards and jaguars, though. The construction of their hyoid bones give them the distinct ability to let out a ferocious roar. That’s something that their purring cousins cannot do. So it seems that there are really 2 kinds of cats in the world – those that can purr, and those that can roar.

Personally, I’m glad my cats are the purring kind.