You may associate purring with feelings of happiness. It can be the ultimate sound of acceptance — that your attention and affection are cherished and appreciated. When you’re petting your cat, brushing her or offering a favorite treat, contentment is likely what your cat is communicating. But cats purr for other reasons.
What are frequencies?
Cats purr at a frequency between 25 and 150 hertz (Hz). You can feel a cat’s purring. What exactly does that mean?
A hertz is a unit for measuring sound waves, also called frequencies. One hertz equals a sound wave moving at one cycle per second. Low frequencies (0 to 500 Hz) are vibrating sounds that you can feel as well as hear, like the bass instruments in a musical band.
Medium frequencies (500 to 2,000 Hz) are within the broader range of human speech, which is somewhere between 250 and 8,000 Hz. High frequencies (2,000 Hz and higher) are the treble instruments of the band — think of clanging cymbals.
Certain frequencies — too high or too low — can be annoying, harmful and even lethal to individuals within earshot. But the reverse is also true. Numerous scientific studies have shown that the right frequencies can soothe stress, relieve pain and promote healing. Therapeutic music and feline purring fall into this frequency range.
A landmark study, “The felid purr: A healing mechanism?” suggested that purring vibrations are at such a frequency that might “promote bone growth and heal soft tissue.” The study was first published in the New Zealand Veterinary Journal and later in the November 2001 issue of The Journal of the Acoustical Society of America. The study’s oft-cited conclusions may be why purring has become the most studied of all feline vocalizations by scholars and researchers.
Receiving the message
In a 2020 study, researchers led by the Korean Society of Veterinary Science, examined 20 feline vocalizations including purring. They published their results in “Feline vocal communication” in the January 2020 Journal of Veterinary Science.
According to the researchers, kittens learn purring from their mothers as early as their first few days of life. Defined as a “low, continuous rhythmical tone produced during respiration,” the sound is produced with closed mouths continuously during inhaling and exhaling, and “increases the respiratory rate during rest.”
Purring can last anywhere from one second or less to a few minutes and can be combined with other vocal tones, although they generally are low pitched. Purring allows kittens and their moms to communicate with each other in close proximity without being heard or detected by predators. In other words, you have to be close to the cat to hear and feel the vibrations and get the message.
Although purring has long been understood to be a sign of friendliness and happiness in cats, “the purr can vary subtly and be used in several situations,” the researchers wrote. Cats not only purr when they “are content and hungry but also in cases of stress, pain or close to death.”
Cats are talented impersonators. For example, chirping vocalizations mimic birds, and meowing simulates human communication. Although I’ve never heard one, several studies refer to a food-solicitation purr, which is higher pitched than typical purring and mimics a human baby’s cries to gain our sympathy.
Because cats purr when in distress or pain and purring is in a healing frequency, some researchers have concluded that purring may be an attempt to self-soothe. It certainly is soothing to me to have a purring cat on my lap.
Purring vs. Roaring
With the exception of the four felids belonging to the Panthera genus, 34 out of the 38 cat species purr. That means cheetahs, cougars, lynx, bobcats, servals and a host of other cat species purr. The four cat species that don’t purr roar.
It turns out that purring and roaring are mutually exclusive and have to do with the anatomy of the voice box. Purring cats’ voice boxes contain an epihyal bone. Roaring cats’ voice boxes lack this bone but instead contain a ligament that stretches to create a larger, lower-pitched sound when air passes over the vocal cords, which are also larger in the bigger cats.
Cat species from the Panthera genus that do NOT purr but ROAR include: