Why Do Cats Purr?

How Cats Purr

There is still so much to learn about cats and purring. In fact, scientists can’t agree on what initiates a purr. There are three ideas:

1. Most common theory: It starts in a neural oscillator in the cat’s brain. This means neurons fire in the brain in a rhythmic pattern.
   
   
2. It’s voluntary, so cats purr when they want (sounds so cat-like, doesn’t it?).
   
   
3. It’s caused by the release of endorphins for pleasure or pain.

Regardless of what initiates it, a cat’s voice box is fixed and the laryngeal muscles in it vibrate, causing space between the vocal cords to open and close.

Air passes through the openings, flowing by the voice box creating a consistent purr sound frequency of 25-100 Hz as the cat inhales and exhales. Since cats with laryngeal paralysis can’t purr, this explanation is the most likely one.

Cats Purr to Communicate

Kittens start purring when they are very young, and it’s likely to let their mother know they’re okay since they can’t meow while nursing. Mothers purr to their kittens, especially in the early days, because kittens can’t see or hear yet. The purr likely communicates safety or that it’s mealtime. Since it’s quiet and unlikely to attract a predator, it’s a great way for the mother to communicate.

Obviously, you’ll most commonly hear a cat purring while getting affection or food from you or relaxing for a nap, all expressing contentment. However, cats also appear to purr to self soothe, since they purr when giving birth or if they’re nervous, upset, injured, sick, or dying.

There’s also a theory that frightened cats purr as a way to communicate to other cats that they are peaceful and don’t want to fight.

Another interesting fact is that scientists at the University of Sussex discovered that cats combine a purr with a meow when they are hungry. They hit 220-520 Hz, which is much higher than normal.

Why would they do that? Well, you know what else cries at a similar frequency? A human baby. Their frequency is 300-600 Hz. They’ve apparently learned that if they do this, we’ll feed them sooner (and we usually do).

Healing Powers

The frequency of a purr is the same frequency shown to improve bone density and even be therapeutic in humans. Now, scientists speculate that cats purr to repair bones, heal wounds, and even relieve pain. Bone responds at 25-50 Hz and soft tissue at 100 Hz.

This would make sense why cats often purr when napping, because it could be a low-energy form of self-repair. Also, purring during labor could help the mother manage her pain, and afterward, help her heal and her kittens grow at the same time! Additionally, it could explain why cats seem to have many less muscle or bone abnormalities than the domestic dog.

But cats don’t just help themselves – they spread the love, helping reduce stress and lowering blood pressure in humans more than other pets. A study at the University of Minnesota Stroke Center discovered that cat owners have a 40% less likely chance of suffering a stroke.

Big Cats: Roar or Purr

Big cats that roar can’t purr, and cats that purr can’t roar. Why is this? It’s related to a bone in the neck and the way their vocal cords are designed.

Many mammals (including humans and domestic cats), reptiles, amphibians, and birds have a hyoid bone in the middle of their neck. It’s a hard U-shaped bone that aids with tongue movement and swallowing. They also have triangular-shaped vocal cords. These are both different in roaring cats.

In big cats like lions, tigers, leopards, and jaguars, the hyoid bone is actually flexible and the epihyal bone in the voice box (which is typically a small bone that supports the hyoid bone) is replaced with a ligament.

The more the ligament stretches, the bigger the air passage is around fleshy, flat, square-shaped vocal cords, resulting in a louder, deeper sound. A roar can reach 114 decibels, which is close to humans’ pain threshold.

The purring group of larger cats includes cheetahs, pums, cougars, mountain lions, and lynxes. Although cheetahs and cougars are considered big cats, they are the smallest of the big cats and actually have a fixed hyoid bone. Researchers aren’t sure why and when cats in the wild purr, though they do know one time they do it is when grooming each other.

There is one except to all of this. Snow leopards have a flexible hyoid bone, but they can’t truly roar or purr, although they make sounds similar to both. Their vocal cords are missing a fatty, elastic layer of tissue that would allow them to make vocalizations like other big cats.

Purrfect Pitch

Regardless of what initiates a purr, if you’re snuggling with your kitty and you start to feel the vibrations, make no mistake – they’re happy to be with you. And if their soothing purr helps comfort your aches and pains and reduce stress, that’s a bonus!