In what must have been one of the simplest and most enjoyable lab experiments ever, researchers found that house cats purr at a frequency of around 25 Hertz (25 times per second). They can keep purring for up to two hours.

To appreciate how amazing that is, imagine yourself humming the same note, without changing pitch as you breathe in and out, for two hours.

The big cats can’t do it, either, though they’re certainly equipped to make a lot of noise. This is why zoologists divided the cat family up into “roaring” and “purring” cats for most of the twentieth century.

It wasn’t a perfect system – some leopard-sized cats, for instance, like the cheetah, can purr – but feline anatomy seemed to back it up. The hyoid bone and some related neck structures are arranged differently in big cats and small cats. It seemed clear that this somehow allowed big cats to roar and smaller cats to purr.

However, more research has shown that muscles and vocal cords are probably involved, not the hyoid bone and its supports.

Small cats twitch a muscle – the vocalis muscle – in their neck. This triggers nearby vocal cords to vibrate, causing a purr. Big cats have the same muscle and the same vocal cords, but their cords are big enough to actually slow down the twitching muscle.

This is why you’ll never hear a lion purr.

Those vocal cords still vibrate, though at a much lower frequency. The rest of the big cat’s vocal tract is also perfectly shaped to deepen the vibrations into one of the most awesome sounds in nature.

Yes, that’s in a zoo, but I like the way this lion ignores the crowd after doing his thing. He is truly above it all.

Featured image: Steffen Wienberg at Pixabay

Sources:

Kitchener, A. C., Van Valkenburgh, B., and Yamaguchi, N.  2010.  Felid form and function, in Biology and Conservation of Wild Felids, ed. D. W. Macdonald and A. J. Loveridge, 83-106.  Oxford:  Oxford University Press, Oxford.