A purr or whirr is a tonal fluttering sound made by some species of

felid Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ). The 41 extant taxon, extant Felidae species exhibit the gre ...

s, including both larger, wild cats and the

domestic cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small Domestication, domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have sh ...

(''Felis catus''), as well as two species of genets. 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 The cheetah (''Acinonyx jubatus'') is a large Felidae, cat and the Fastest animals, fastest land animal. It has a tawny to creamy white or pale buff fur that is marked with evenly spaced, solid black spots. The head is small and rounded, wit ...

, it is called a whirr. Although true purring is exclusive to

s and viverrids, other animals such as raccoons produce vocalizations that sound similar to true purring. Animals that produce purr-like sounds include

mongooses A mongoose is a small terrestrial carnivorous mammal belonging to the Family (biology), family Herpestidae. This family has two subfamilies, the Herpestinae and the Mungotinae. The Herpestinae comprises 23 living species that are native to sou ...

kangaroo Kangaroos are marsupials from the family Macropodidae (macropods, meaning "large foot"). In common use, the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern gre ...

s, wallabies, wallaroos,

badger Badgers are medium-sized short-legged omnivores in the superfamily Musteloidea. Badgers are a polyphyletic rather than a natural taxonomic grouping, being united by their squat bodies and adaptions for fossorial activity rather than by the ...

rabbit Rabbits are small mammals in the family Leporidae (which also includes the hares), which is in the order Lagomorpha (which also includes pikas). They are familiar throughout the world as a small herbivore, a prey animal, a domesticated ...

s and

guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy ( ), is a species of rodent belonging to the genus ''Cavia'', family Caviidae. Animal fancy, Breeders tend to use the name "cavy" for the ani ...

s. 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. Purring is a soft buzzing sound, similar to a rolled 'r' in human speech, with a

fundamental frequency The fundamental frequency, often referred to simply as the ''fundamental'' (abbreviated as 0 or 1 ), is defined as the lowest frequency of a Periodic signal, periodic waveform. In music, the fundamental is the musical pitch (music), pitch of a n ...

of around 25 Hz. This sound occurs with noticeable vibrations on the surface of the body, varies in a rhythmic pattern during breathing and occurs continuously during inhalation and exhalation. The intensity and length of the purr can also vary depending on the level of arousal of the animal.

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 Neural oscillations, or brainwaves, are rhythmic or repetitive patterns of neural activity in the central nervous system. Neural tissue can generate oscillation, oscillatory activity in many ways, driven either by mechanisms within individual ne ...

" in the cat's brain of uncertain significance. Although the mechanism has not yet been fully explained, recent studies have inferred it could be the result of oscillatory mechanisms in the central nervous system. Studies have also shown that purring can be caused through electrically stimulating the infundibular region of the cat's brain, suggesting central control.

Vocal folds/laryngeal muscles

One hypothesis, backed by electromyographic studies, is that cats produce the purring noise by using the

vocal folds In humans, the vocal cords, also known as vocal folds, are folds of throat tissues that are key in creating sounds through Speech, vocalization. The length of the vocal cords affects the pitch of voice, similar to a violin string. Open when brea ...

or the muscles of the

larynx The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...

to alternately dilate and constrict the

glottis The glottis (: glottises or glottides) is the opening between the vocal folds (the rima glottidis). The glottis is crucial in producing sound from the vocal folds. Etymology From Ancient Greek ''γλωττίς'' (glōttís), derived from ''γ ...

rapidly, causing air vibrations during inhalation and exhalation. Combined with the steady inhalation and exhalation of air as the cat breathes, a purring noise is produced with strong

harmonics In physics, acoustics, and telecommunications, a harmonic is a sinusoidal wave with a frequency that is a positive integer multiple of the ''fundamental frequency'' of a periodic signal. The fundamental frequency is also called the ''1st harm ...

Degree of hyoid ossification

No cat can both purr and

roar A roar is a type of animal vocalization that is loud, deep and resonating. Many mammals have evolved to produce roars and other roar-like vocals for purposes such as long-distance communication and intimidation. These include various species of ...

. The subdivision of the Felidae into "purring cats" (

Felinae The small cats or Felinae are a subfamily of Felidae distinguished by their bony hyoids, which let them purr but not roar. Other authors have proposed an alternative definition for this subfamily, as comprising only the living conical-toothed cat ...

) on one hand and "roaring cats" (

Pantherinae The Pantherinae is a subfamily of the Felidae; it was named and first described by Reginald Innes Pocock in 1917 as only including the ''Panthera'' species, but later also came to include the clouded leopards (genus ''Neofelis''). The Pantherin ...

) on the other goes back to Owen and was definitively introduced by Pocock, based on whether the

hyoid bone The hyoid-bone (lingual-bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid-cartilage. At rest, it lies between the base of the mandible and the third cervical verte ...

of the

is incompletely ("roarers") or completely ("purrers")

ossified Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in t ...

. 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 The snow leopard (''Panthera uncia'') is a species of large cat in the genus ''Panthera'' of the family Felidae. The species is native to the mountain ranges of Central and South Asia. It is listed as Vulnerable on the IUCN Red List because ...

(''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

*Domestic cats purr at a

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

of 20 to 30 vibrations per second. *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). *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. *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 & 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.

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

nursing Nursing is a health care profession that "integrates the art and science of caring and focuses on the protection, promotion, and optimization of health and human functioning; prevention of illness and injury; facilitation of healing; and alle ...

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. This variety of purring seems to be found more frequently in cats in a one-to-one relationship with a caretaker. Similarities have been drawn between an infant's cry and the isolation cry of domestic cats. The high-frequency aspect of the purr may subtly exploit humans' sensitivity to these cries. Using sensory biases in communication between species provides cats with a productive means of improving the care that they receive. Cats often purr when distressed or in pain, such as during the three stages of

labor Labour or labor may refer to: * Childbirth, the delivery of a baby * Labour (human activity), or work ** Manual labour, physical work ** Wage labour, a socioeconomic relationship between a worker and an employer ** Organized labour and the labour ...

. 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.

References

External links

Why do cats purr? Why do Cheshire cats grin?

Robert Eklund's Purring Page
{{Authority control Animal sounds Cat behavior Ethology