There seems to be an abundance of information about why cats purr, but discovering how cats purr was more tricky. With both topics came an air of mystery and uncertainty, because, perhaps, cats have not been as thoroughly studied as primates or rodents. And while I’m on this tangent, I’ll complain about the disproportionate amount of cat books compared to the dog books at the library. Two measly shelves was all I had to draw from for cat information, and what was there seemed to be different versions a book entitled something like I just got a Kitty! What should I do with it? One of the cat books was even written by a dog trainer (an obnoxiously self-obsessed one, at that)! It was pretty horrifying.
So, returning to the question, how do cats purr…
The sound is produced by triggering the glottis (or vocal folds) to open and close using the larynx and diaphragm muscles, that is, the muscles surrounding the lung cavity and in the area colloquially known as the voice box. This muscular “tremor” occurs at a frequency of 25 to 150 Hertz, and appears to be a behavior that the cat can voluntarily trigger and cease.
Some research has been done to determine what members of the felid group, other than the domestic cat, make such noises. Because of the physiology and behavioral patterns of each feloidea being so different, in addition to the sparse availability of data on the subject, it is really only safe to say that most felids make some kind of purr-like noise for some reason.
What sources do agree upon is that purring in domestic cats normally occurs during relaxed or pleasurable moments, for example, during grooming, suckling, or receiving affection from humans, but that there are also occasional incidences of purring in painful situations. And that fact has lead many to suggest some interesting ideas on the purpose of purring, especially the idea that it is a recovery or recuperation response. In other words, purring may have a healing (or at least soothing) effect on the afflicted cat.
Another intriguing theory is that purring may have evolved to prevent muscle atrophy during a cat’s long sleep periods (but this theory, perhaps, falsely assumes that cats purr while sleeping), and purring may also serve to strengthen bone density. Several articles have also suggested that purring is used as a means of communication not only between the mother and her kittens, but between a domestic cat and a human. When my Harry wakes me up every morning, for example, he does so using his feed me purr, which seems to me to be very forced and urgent. Harry has a separate and distinct purr that is a far more relaxed and happy signal. Similarly, there is research suggesting that the frequency of the feed me purr is similar to the frequency of a baby’s cry and is therefore highly perturbing to humans.
Gary, Stuart, and Vanessa Barrs. “How Do Cats Purr?”ABC Science. 31 May 2011. <http://www.abc.net.au/science/articles/2011/05/31/3231616.htm>.
Lyons, Leslie A. “Why Do Cats Purr?: Scientific American.” Scientific American. 7 Jan. 2003. <http://www.scientificamerican.com/article.cfm?id=why-do-cats-purr>.
Peters, G. “Purring and Similar Vocalizations in Mammals.” Mammal Rev. 32.4 (2002): 245-71. Print.
Image by Cofaru Alexandru