Purring is one of the most famous sounds that cats make. After constant, loud meowing, that is. Usually, we think of purring as a sign of calmness and contentedness. But what is going on, and why do cats purr? Let’s find out!
From an evolutionary perspective, purring may appear wrong on the surface. Animals need to survive. To survive means to find food and not to become food for someone else. For the latter purpose, making noise when you are to doze off seems completely illogical.
Yet, cats purr. And on many occasions.
When, how and why cats purr
We first wanted to make a list of situations when cats purr. However, it came out rather long. It’s easier to say that cats can purr in many contexts.
Here are few groups of situations when cats purr: when they are content, greet us, or other cats, when they nurse or give birth, doze off, beg food from humans, and even when they are severely ill and dying.
Thus we are curious to ask, do cats purr all the time? Certainly a lot, but we do know that they don’t when they are aggressive or have sex.
Cats can purr both when breathing in and out, and it happens when air passes through their windpipe and laryngeal muscles rapidly alternate the shape of its top opening. This rapid alteration is what makes this vibrating “prrrrrrrrrr…” sound. Each tone change corresponds to an anatomical shape change. That is lightning fast.
Interestingly, house cats are not the only ones that purr. Most smaller wild cats do, and pumas and jaguars also purr. That coincides with the fact that they are house cat’s closest relatives among big cats. Other large cats, like lions and tigers, can’t purr. But they can roar, which is similar to purring in the way how the sound is made.
As you see from the list of occasions when cats purr, there is a wide variety of possible explanations why they do it. The current understanding is that purring is communication.
Primarily, purring communicates calmness, though it can carry various messages. Similarly, for example, we cannot straightforwardly answer why a cat’s meow or humans yell. In general, they do it to tell something, yet what that something is, depends on the situation.
Purring likely first appeared as kittens communicating to their mothers during nursing, yet gained additional functions through the evolution. For example, cats purr when they beg food and is indeed effective. Can you relate?
Other functions of purring
Purring while begging food is a classic example of animal learning. Cats purr most of the time, and the sound likely reminds the owner to feed the cat. If the pattern continues, the cat quickly learns to intensify purring, and the owner finds that it is hard to resist — the sound of purring is irresistible, unbearable, and hypnotic.
There might be other functions of purring, as well. You may have heard that purring promotes bone density and healing. But is it so?
Does purring heal? It’s a broad topic, but we’ll try to keep it short here. The idea that purring may be healing comes from a study that measured the frequency and spreading of vibrations through the cat’s body. They found that cats purr at frequencies between 25 and 150 Hz, which coincides with frequencies that are used (with mixed results) in human medicine to promote bone healing.
The researchers speculated, but by no means concluded that purring serves as a self-healing mechanism for cats. Yet, even more, not even close they mentioned that a cat purring on your lap could heal you.
At the same time, cats do purr during stressful situations, and when they need to calm down. Generally, it does make sense. For example, we also hum when we are stressed, and it helps to calm ourselves. Do cats purr to calm themselves? The answer is maybe. Purring likely serves a little more than only communication. Yet, we quite don’t know it.