Are cats the only animals that purr?

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There's plenty of things to love about cats, and purring is definitely one of them. Cat owners can always tell when their pet is happy from their low, contented hums. But do any other animals purr?
The answer depends on how exactly you define "purr," said Jonathan Losos, a professor of biology at Washington University in St. Louis and author of "The Cat's Meow: How Cats Evolved from the Savanna to Your Sofa" (Viking, 2023)
"If the question is, 'what animals purr,' I would respond by, 'what do you mean by purr?'," Losos told Live Science.
The first important component of a purr is its context. Cats are known to purr when they're happy, but they can also purr when they're stressed or in pain. Cats start purring shortly after birth, and both mothers and kittens often purr while locating each other and during nursing.
The second component of a purr is its physical mechanism. Scientists still don't fully understand how cats purr, but an important feature of purring is vibration of the larynx, the structure in the throat known as the voice box in humans. Unlike most other animal vocalizations, which happen only during exhalation, purrs happen continuously as the cat breathes in and out.
"It's very constant, and that's really one of the signatures of a cat purring," Losos explained.
Related: Why do cats purr?
That continuous sound makes felines unique in their ability to purr. Domestic cats (Felis catus), however, aren't the only cat species that purr — wild cats such as cheetahs (Acinonyx jubatus), cougars (Puma concolor), servals (Leptailurus serval) and bobcats (Lynx rufus) can all purr, too.
Some scientists think that instead of categorizing different species as "big" or "small" cats, it's actually more accurate to classify cats as "purring" or "roaring." Lions (Panthera leo), tigers (Panthera tigris), jaguars (Panthera onca) and leopards (Panthera pardus) can't purr, but they can roar, likely due to the anatomy of a structure in their throat called the hyoid.
Outside of the cat family tree, though, continuous purring vocalizations are very rare. The only other animal that's known to purr during inhalation and exhalation is a distant cousin of cats called a genet (genus Genetta).
"They are delightful little animals," Losos said. He described their appearance as a cross between a cat and a mongoose, with long, pointed noses and slender bodies. There are at least two species of genets that are known to purr, Losos said, although it's possible there are more whose purrs haven't been documented by researchers yet.
True purring is unique to cats and genets. But with a looser definition of purring that doesn't focus on the continuous vibration during both inhalation and exhalation, there are many species across the animal kingdom that also make buzzing, rumbly noises, often in similar contexts to cat purring.
Raccoons (Procyon lotor), for example, "purr" when they're happy and relaxed, usually when babies are with their mothers. Suzanne MacDonald, a professor of psychology at York University who regularly works with raccoons, even witnessed an orphaned baby raccoon "purr" while she hand-fed it.
"They don't sound exactly like cats purring, but pretty close!" MacDonald told Live Science in an email. "When you hear it, you know you're doing something right."
There's not much research on raccoon "purring," but MacDonald believes the sound comes from a combination of a raccoon vocalization called a chitter and excess saliva from the raccoons being very relaxed — a very different mechanism to how felines purr.
Many other mammals make vibrating noises to express comfort. For example, some rabbit owners report their pets rapidly chatter their teeth together when they're relaxed, creating a vibrating sound similar to a purr. Bats can "purr" when being held by a trusted human, one bat expert told The Irish Times. And researchers have noted that when mother and kit gray squirrels (Sciurus carolinensis) are together, they make a purring-like sound called a "muk-muk."
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Some animals that "purr" aren't even mammals. Take wolf spiders (Gladicosa gulosa), which, when attracting potential mates, strike specialized body parts against each other to make a purring sound, similar to how crickets create their chirps.
While many animals do make noises that share some resemblance to cat purrs, there's still a lot of questions. Because many animals make these vibrating noises when they're relaxed, it's a difficult behavior to study, because the presence of human researchers can inherently stress animals out.
But one thing is clear: By the strict definition of purring, cats really are special.