A purr or whirr is a tonal fluttering sound made by some species of , including both larger, wild cats and the domestic cat ( Felis catus), as well as two species of genets and the Caquetá titi monkey ( Plecturocebus caquetensis). It varies in loudness and tone among species and in the same animal. In smaller and domestic cats it is known as a purr, while in larger felids, such as the cheetah, it is called a whirr.
Although true purring is exclusive to Felidae and viverrids,
Animals purr for a variety of reasons, including to express happiness or fear, and as a defense mechanism. It has also been shown that cats purr to manage pain and soothe themselves.
Mechanism
The mechanism by which cats purr is an object of speculation, with different hypotheses proposed. An early idea was that purring is a hemodynamic process where sound is produced as the blood runs through the thorax.
There is a unique "neural oscillator" in the cat's brain of uncertain significance.
Vocal folds/laryngeal muscles
One hypothesis, backed by electromyographic studies, is that cats produce the purring noise by using the
vocal folds or the muscles of the
larynx to alternately dilate and constrict the
glottis rapidly, causing air vibrations during inhalation and exhalation.
[K.M. Dyce, W.O. Sack and C.J.G. Wensing in Textbook of Veterinary Anatomy 3rd Ed. 2002, Saunders, Philadelphia; p156] Combined with the steady inhalation and exhalation of air as the cat breathes, a purring noise is produced with strong
harmonics.
Degree of hyoid ossification
No cat can both purr and roar. The subdivision of the Felidae into "purring cats" (
Felinae) on one hand and "roaring cats" (
Pantherinae) on the other goes back to Owen
and was definitively introduced by Pocock,
based on whether the
hyoid bone of the
larynx is incompletely ("roarers") or completely ("purrers")
ossified. However, Weissengruber et al. argued that the ability of a cat species to purr is not affected by the anatomy of its hyoid.
The "roaring cats" (lion, Panthera leo; tiger, P. tigris; jaguar, P. onca; leopard, P. pardus) have an incompletely ossified hyoid, which, according to this hypothesis, enables them to roar but not to purr. However, the snow leopard ( Uncia uncia, or P. uncia), as the fifth felid species with an incompletely ossified hyoid, purrs.
All remaining species of the family Felidae ("purring cats") have a completely ossified hyoid, which enables them to purr but not to roar. Based on a technical acoustic definition of roaring, the presence of this vocalization type depends on specific characteristics of the vocal folds and an elongated vocal tract, which is rendered possible by an incompletely ossified hyoid.
Frequency, amplitude, and respiratory variation
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Domestic cats purr at a frequency of 20 to 30 vibrations per second.
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Eklund, Peters & Duthie, comparing purring in a cheetah ( Acinonyx jubatus) and a domestic cat ( Felis catus) found that the cheetah purred with an average frequency of 20.87 Hz (egressive phases) and 18.32 Hz (ingressive phases), while the much smaller domestic cat purred with an average frequency of 21.98 Hz (egressive phases) and 23.24 Hz (ingressive phases).
[Eklund, Robert, Gustav Peters & Elizabeth D. Duthie. 2010. An acoustic analysis of purring in the cheetah (Acinonyx jubatus) and in the domestic cat (Felis catus) , Proceedings of Fonetik 2010, 2–4 June 2010, Lund University, Lund, Sweden, pp. 17–22.]
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Schötz & Eklund studied purring in four domestic cats and found that the fundamental frequency varied between 20.94 and 27.21 Hz for egressive phases and between 23.0 and 26.09 Hz for ingressive phases. Schötz & Eklund also observed considerable variation between the four cats as regards relative amplitude, duration and frequency between egressive and ingressive phases, but that this variation occurred within the same general range.
[Schötz, Susanne & Robert Eklund. 2011. A comparative acoustic analysis of purring in four cats . Proceedings of Fonetik 2011, 8–10 June 2011, Royal Institute of Technology, Stockholm, Sweden, pp. 9–12.]
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In a follow-up study of purring in four adult cheetahs, Eklund, Peters, Weise & Munro found that egressive phases were longer than ingressive phases in all four cheetahs. Likewise, ingressive phases had a lower frequency than egressive phases in all four cheetahs. Mean frequency were between 19.3 Hz and 20.5 Hz in ingressive phases, and between 21.9 Hz and 23.4 Hz in egressive phases. Moreover, the amplitude was louder in the egressive phases in four cheetahs.
[Eklund, Robert, Gustav Peters, Florian Weise & Stuart Munro. 2012. A comparative acoustic analysis of purring in four cheetahs , Proceedings of Fonetik 2012, 30 May–1 June 2012, Gothenburg University, Gothenburg, Sweden, pp. 41–44.]
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Eklund & Peters compared purring in adult, subadult and juvenile cheetahs and reported that while there was considerable variation across most of the parameters analyzed (amplitude, phase duration, cycles per phase and fundamental frequency) – mainly attributable to degree of relaxation/agitation in the animals resting or playing– previously reported observations that ingressive phases tend to be lower in frequency were largely confirmed. There were no major differences in these parameters as a function of age.
[Eklund, Robert & Gustav Peters. 2013. A comparative acoustic analysis of purring in juvenile, subadult and adult cheetahs . In: Robert Eklund (ed.), Proceedings of Fonetik 2013, the XXVIth Swedish Phonetics Conference, Studies in Language and Culture, no. 21, , , ISSN 1403-2570, pp. 25–28.]
Purpose
In domestic cats, many signals that occur when interacting with humans seem to originate from when the animal was dependent on the mother. Cats have been observed to purr for most of their lifespan, starting from when they were young and suckling from their mother.
Purring may be a signaling mechanism of reassurance between mother cats and
Lactation kittens. Post-nursing cats often purr as a sign of contentment when being petted, becoming relaxed or eating. Some purring may be a signal to another animal that the purring cat does not pose a threat.
Cats have been shown to have different types of purrs depending on situations. For example, purring appears to be a way for cats to signal their caretakers for food. This purring has a high-frequency component not present in other purrs. These are called solicitation purrs (when the cat is seeking a result) and non-solicitation purrs, and the two are distinguishable to humans. In a study, 50 humans were subjected to playbacks of purrs recorded in solicitation and non-solicitation situations at the same amplitude. Humans regularly judged the solicitation purrs as less pleasant and more urgent than the non-solicitation purrs.
Cats often purr when distressed or in pain, such as during the three stages of Birth. In the first stage, the uterus begins to contract, the cervix relaxes, the water breaks and the cat begins to purr. The female cat (queen) will purr and socialize during the first stage of labor. The purring is thought to be a self-relaxation technique.
See also
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Cat communication
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Kneading
Further reading
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Stogdale L, Delack JB. Feline purring. Compendium on Continuing Education for the Practicing Veterinarian 1985; 7: 551–553.
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Reprinted in: Voith VL, Borchelt PL (eds). Readings in Companion Animal Behavior. Trenton: Veterinary Learning Systems, 1996; 269–270.
External links
