is a sound made by all species of felids and is a part of cat communication
Cat communication is the range of methods by which cats communicate with other cats, humans, and other animals. Communication methods include postures, movement , and auditory and chemical signals.The communication methods used by cats have been affected by the domestication process.-Auditory...
. It varies between cats (for example by loudness and tone), and from species to species, but can be characterized as a tonal buzzing. Domestic cats purr in a frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
of 25 to 150 vibrations per second. Eklund, Peters & Duthie (2010)
, 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
In human speech, egressive sounds are sounds by which the air stream is created by pushing air out through the mouth or nose. The three types of egressive sounds are pulmonic egressive , glottalic egressive , and lingual egressive...
phases) and 18.32 Hz (ingressive
In human speech, ingressive sounds are sounds by which the air stream flows inward through the mouth or nose. The three types of ingressive sounds are lingual ingressive or velaric ingressive , glottalic ingressive , and pulmonic 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 (2011)
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 (2011) also observed considerable variation between the four cats as regards relative amplitude, duration and frequency between egressive and ingressive phases, but that this variation generally occurred within the same general range. For film clips of purring waveforms, see purring.org
The term "purring" has been used liberally in literature, and it has been claimed that viverrids (civet, mongoose, genet), bears, badgers, hyaenas (et cetera) purr. Other animals that have been said to purr are rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...
s, squirrels, guinea pigs, tapirs, ring-tailed lemurs, elephants, raccoons and gorillas while eating. However, using a strict definition of purring that continuous sound production must alternate between pulmonic egressive and ingressive airstream
(and usually go on for minutes), Peters (2002), in an exhaustive review of the scientific literature, reached the conclusion that until then only ‘purring cats’ (Felidae) and two species of genets
Genets are Old World mammals from the order Carnivora, family Viverridae, related to civets and linsangs. All species are contained within the genus Genetta, although the Aquatic Genet is sometimes housed in its own genus Osbornictis....
, Genetta tigrina
, and most likely also Genetta genetta
, had been documented to purr.
Although purring is a universally recognized phenomenon, the mechanism by which cats purr is elusive. This is partly because the cat has no unique anatomical feature that is clearly responsible for the sound.
One hypothesis, backed by electromyographic studies, is that cats produce the purring noise by using the vocal folds
The vocal folds, also known commonly as vocal cords, are composed of twin infoldings of mucous membrane stretched horizontally across the larynx...
and/or the muscles of the larynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...
to alternately dilate and constrict the glottis
The glottis is defined as the combination of the vocal folds and the space in between the folds .-Function:...
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. Purring is sometimes accompanied by other sounds, though this varies from cat to cat; in the audio samples that accompany this article, the first cat is only purring, while the vocal production of the second cat contains low level outbursts sometimes characterized as "lurps" or "yowps".
It was, until recent times, believed that only the cats of the Felis
Felis is a genus of cats in the family Felidae, including the familiar domestic cat and its closest wild relatives. The wild species are distributed widely across Europe, southern and central Asia, and Africa; the domestic cat has been introduced worldwide.Members of the genus Felis are all small...
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
could purr. However, felids of the Panthera
Panthera is a genus of the family Felidae , which contains four well-known living species: the tiger, the lion, the jaguar, and the leopard. The genus comprises about half of the Pantherinae subfamily, the big cats...
genus (Tiger, Lion, Jaguar and Leopard) also produce sounds similar to purring, but only when exhaling. The subdivision of the Felidae into ‘purring cats’ on the one hand and ‘roaring cats ’ (i.e. non-purring) on the other, originally goes back to Owen (1834/1835) and was definitely introduced by Pocock (1916), based on a difference in hyoid
The hyoid 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 at the level of the base of the mandible in the front and the third cervical vertebra behind.Unlike other bones, the hyoid is only distantly...
anatomy. The ‘roaring cats’ (lion, Panthera leo
; tiger, P. tigris
; jaguar, P. onca
; leopard, P. pardus
) have an incompletely ossified hyoid, which according to this theory, enables them to roar but not to purr. On the other hand, the snow leopard
The snow leopard is a moderately large cat native to the mountain ranges of South Asia and Central Asia...
, or P. uncia
), as the fifth felid species with an incompletely ossified hyoid, purrs (Hemmer, 1972). All remaining species of the family Felidae (‘purring cats’) have a completely ossified hyoid which enables them to purr but not to roar. However, Weissengruber et al. (2002) argued that the ability of a cat species to purr is not affected by the anatomy of its hyoid, i.e. whether it is fully ossified or has a ligamentous epihyoid, and that, 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, the latter rendered possible by an incompletely ossified hyoid.
Nobody knows for certain why cats purr, but the following reasons are speculated:
Cats often purr when being patted, becoming relaxed, or when eating. Female cats are known to sometimes purr while giving birth
Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...
. Domestic cats have been reported to purr when injured, sick, in pain or dying. Purring may have developed as a signalling mechanism between mother cats and nursing
Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
kittens. One theory is that it is not a sign of showing relaxation or content, but an attempt at "friendship" or a signal of "specific intent". For example, when a cat is nervous and cannot escape the situation (at a veterinarian perhaps), its purr may serve as an attempt to avoid being hurt. German ethologist and cat behaviorist Paul Leyhausen interprets it as a signal that the animal is not posing a threat.
Scientists at the University of Sussex
The University of Sussex is an English public research university situated next to the East Sussex village of Falmer, within the city of Brighton and Hove. The University received its Royal Charter in August 1961....
showed in 2009 that purring, or some purring, seems to be a way for domesticated cats to signal their owners for food. According to Dr. Karen McComb and her team, purring in the "about to be fed" context has a high-frequency component not ordinarily present. Humans report feeling an urgency to investigate and satisfy the cat's needs; to wit: "feed me." However, this variety of purring seems to be found only in cats in a one-on-one relationship with their caretakers. This "soliciting purr" is different from a cat's normal purring. Another theory states that purring triggers a cat's brain to release a hormone which helps it in relaxing and acts as a pain killer. This may be a reason why cats purr when distressed or in labour.
Roger A. Caras opines that cats purr in response to profound emotions.