Why Do Cats Purr and How Do Cats Purr?

(Last Updated On: February 6, 2019)

Why do cats purr? For most, the answer might seem pretty simple. Because they are happy! But it turns out, our feline friends are a bit more complex than people commonly assume.

Why Do Cats Purr?

Sure, cats do purr when they are happy or comfortable. But there are actually other reasons that might cause a cat to purr. Cats also purr when they are fearful or anxious, or when they feel threatened, like when they are placed in an unknown environment or taken for a trip to the vet.

Why is this? Consider the purr from a cat like a human smile. Humans will often smile in situations when it seems counterintuitive to do so, like when they they feel uncomfortable or nervous. Essentially, the same is likely true for cats. Some veterinarians even believe that a cat might sometimes purr to appease their owner. If this is true, it refutes the theory that cats are less concerned about the wellbeing of their human partners than dogs are.

Furthermore, when a cat is seeking human attention, they are known to produce what is called a “solicitation purr”. This odd noise is essentially a purr combined with meow, and cat owners are almost just as likely to respond to it as they are to a human baby crying. Not surprisingly, scientists have discovered the frequency range of this unique sound falls within 220-520 hertz. This is a similar range to a human baby’s cry, which generally occurs at about 300-600 hertz. While it can’t be proven that cat’s create this sound specifically to play on the sympathies of humans, the similarities suggest coevolution in action.

However, none of this actually answers the question of why cats evolved the ability to purr in the first place. In this respect, scientists believe that the cat’s purr likely emerged as a favorable adaptation mechanism in that it served as an easy way to convey emotional states to their young.

How Do Cats Purr?

It turns out that cats are uniquely hardwired to be able to produce this satisfying vibration. The brain will send a signal to the voicebox via a repetitive neural oscillator. This vibration will cause the laryngeal muscle to move at a rate as fast as up to a hundred times a second. This vibration results in the vocal cords separating in both the inhale and exhale, effectively transforming the cat’s voice box into a temporary air valve.

Furthermore, just like a human voice, every cat purr is unique. Some cats purr at a high vibration, and some purr at a low vibration. Essentially, while all purring sounds tend to occur between a frequence of 25-150 hz, every purr has its own unique vibrational footprint and no two cats sound exactly alike when they purr.

That said, not all cats can purr, and not all species that can purr are cats. As a general rule, cats that roar can’t purr, and cat’s that purr can’t roar. Why is this? Essentially, in order to be able to produce a roar, the larynx needs to be structured in a way that is incongruent with how it needs to be wired to purr. Cats that roar need to move far distances to find prey, and as such, the importance of being able to communicate loud and clear the boundaries of their territory trumps the need to purr in terms of survival. For smaller species, prey is not so scarce, and scent marking is all that is necessary to establish territory.

This means that all domestic cats can purr, but only a handful of smaller wildcats can. However, some smaller cousins to the cat like mongoose, racoons and even hyenas can purr as well.

Why Does Purring Feel Good?

Most people won’t argue with the statement that a cat’s purr is a satisfying sound. And apparently the same is true for cats. Many female cats will purr during the process of giving birth, which is believed to have a relaxing effect on the cat in an otherwise stressful and painful event. In other words, cats are likely to use the purr as a way to self-sooth.

In fact, the most common frequency range of the purr is associated with greater bone density and faster healing. So the cat’s purr might indeed be good for cats as well as humans. This might help explain why it tends to sound so pleasing.

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