When do cats purr

How and why do cats purr?

Cat cats do it, desert lynx and lynx, ocelots as well as the medium-sized serval and the more than medium-sized pumas and cheetahs: purr. Just why - and how exactly? In fact, to this day, cat researchers argue about what purring is really all about. In principle everything is clear, but all sorts of details remain controversial.

Every cat lover knows, of course, the cozy purring of his full and petted favorite. But the attentive has not escaped the fact that hangovers and co purr in completely different situations: when they are hungry, injured, frightened or all of that at once. Obviously, purring fulfills several tasks at the same time, regardless of the well-being of the animal and the owner.

All sorts of neuro-anatomical things

But briefly away from the "why": Even "how" the cat purrs was not really clear for a long time. At some point it was clear that the cord tract results from a subtle diversion of the airflow, for which the anatomy is somehow clamped between the diaphragm and the larynx. However, decades of cat purr research failed when trying to explain exactly why the typical continuous, sonorous whirring results. The most common hypotheses to this day state that appropriate rhythmic vibrations of the "real pair of vocal cords", amplified by resonance spaces, are the cause. Alternatively, it was assumed that the "wrong" "atrial fold" characteristic of cats was involved in a similar way. Then it was said from different sides that the hyoid bone, the blood flow in the lungs or the main artery would play a role in modulating the normal cat sounds for purring.

For now, most string experts favor a theory involving larynx anatomy and regular nerve impulses. According to this, the vocal cords stretched over the larynx actually make a sound, but this is true both when exhaling and when inhaling in the air stream - incidentally, a rarity of animal sound production that only occurs in smaller cats. The sonorous regularity results from the constant input of neural impulses that are generated with a kind of semi-autonomous free-wheeling neuro-oscillator.

With the help of their muscles, the animals set the vocal folds in their larynx in a rhythmic oscillation: This opens and closes the glottis between the two lips, and we hear the vibration as a purr. The neural clock only has to be switched on and off by higher centers of the cat's brain in order to start and stop its work, whereupon cats then effortlessly hold the sound for seconds to several minutes. Incidentally, exact measurements confirm short, crisp switching phases between the exhalation and inhalation phases of the cycle. In domestic cats, however, they are shorter than 50 milliseconds, so they escape the prickly ears of animal friends caressing them.

You can see that purring is a very complicated matter, and before the cat can do it, the neuromuscular system has to get used to it. Young animals therefore have to practice for a few days before they sound like the big ones. Then the vibrations produced by the vocal cords under neuronal control and modulated by the larynx resonance body become a proper purr - where "proper" means a typical frequency of 16 to 28 Hertz. The exact value varies from species to species (house cats usually clock around 26 Hertz), but not with the size of an animal.

What does it bring - and what does it cost?

Purring is anatomically complex, has to be learned first and therefore demands something from the animal - in return it should be useful to the cat somehow. Perhaps a cat calms down and rewards itself by purring auto-suggestively? After all, cat psychologists observe a calming influence on cat owners such as fur balls, which ultimately leads to the obviously mutually desirable bonding between the animal and a helpful caregiver who has mutated into a voluntary petting slave and can opener.