Cats’ deep purrs have been an unexplained phenomenon for decades. Now researchers have managed to uncover the secret.
If you scratch a cat on the head, cheeks, or chin, you will often hear a deep, unmistakable hum of thanks. Their purr is a kind of love song sung in silence and expressing security. It creates a soothing atmosphere and eliminates stress and anxiety, even if the “feel good” tune sometimes sounds like a rattling engine.
Cats are adept at producing deep, low-frequency sounds, which only occur in animals with larger vocal cords, such as elephants or blue whales. But how do relatively small house tigers manage to make such unmistakable sounds? After all, most domestic cats are not giants of the animal world, but rather diminutive creatures whose average weight reaches about 4.5 kg.
One was recently published in the journal Current Biology. Stady can finally provide an answer. Accordingly, domestic cats have “cushions” built into their vocal folds, which form an additional layer of connective tissue. This enables them, despite their small stature, to produce very low-frequency sounds, which are particularly popular with larger animals. Among their feline relatives, the lynx and leopard can also make strange purring sounds, while tigers and lions roar loudly and powerfully.
When domestic cats communicate with each other and their environment, they usually do so through meowing, hissing, or screaming. Sound production is exactly the same as in humans and many other mammals and, in principle, is nothing special. In cats, sound is also produced in the larynx, which is the connection between the throat and the windpipe.
In order for anything to be heard at all, the flowing breathing air causes the vocal cords to vibrate and collide with each other, for example, 125 times per second (125 Hz), thus producing sound. If you look at the larynx from above, the vocal folds look like a slightly open curtain that opens and closes with the help of the vocal cords and laryngeal muscles. Depending on the exact position in which the vocal folds are fixed, different tones are produced. Along with tongue and mouth movements, very different sounds, noises and volumes can be produced, and – in humans – vowels can also be formed.
In childhood, the vocal cords in boys and girls remain the same length and can be higher than those in adults.
“The role played by the length of the vocal cords can be easily heard in humans,” explains vocal researcher Christian Herbst of the University of Vienna. In childhood, the vocal cords in boys and girls remain the same length and can be higher than those in adults. It is only during puberty that the larynx grows, which means that the vocal cords become longer and the voice becomes deeper – and an audible voice drop occurs, especially in boys. The fundamental pitch of the male voice is on average about 120 Hz, and that of the female voice is about 200 Hz.
In contrast to mammals, songbirds can produce two sounds at the same time or switch very quickly from one sound to another because their sound-producing organ is located directly at the opening of the trachea and each produces its own sounds at the same volume. Bronchi. According to the Max Planck Institute for Biological Intelligence, the golden-winged piper of South America has the loudest song at 11,900 Hz, and the bare-throated parachutist of Central America has the lowest song at 200 Hz. For comparison: A cat, on the other hand, can make sounds about ten times deeper when it purrs.
Deep raspy sounds
A cat’s deep purr has always been considered unusual. Research dating back half a century suggests that domestic cats contract and relax their laryngeal muscles about 30 times per second (30 Hz) to purr. But as Viennese scientist Christian Herbst discovered in collaboration with an international team with Swiss participation in a controlled laboratory experiment, this does not necessarily have to be the case. Initial neural input is sufficient to make the vocal cords vibrate in a self-sustained manner. “Once started, the vocal cords continue to vibrate, similar to a meow,” Herbst explains.
But how does the deep bass come in? Pillow-like accumulations in cats’ vocal cords are hypothesized to increase the biomechanical properties of the tissue, resulting in slower vibrations and very low-frequency sounds despite the animals’ relatively small size. With a little practice, people can also get such a deep voice when speaking. For example, the so-called vocal fry, known in German as Strohbass or Schnarrstimme, which is added at the end of words and is known by women in American television soap operas or also used as an effect in some singing styles of pop music.