Cat Silhouette

Purring.org

Cat Silhouette

Purring waveform

Devoted to felid purring

Robert Eklund, PhD, MA, BA

http://roberteklund.info

Updated: 8 May 2016


This site aims at summarizing what is currently known about (mostly) felid purring, i.e. the “trademark” sound produced by most species of cats, only excluding four or five of the biggest cats, the so-called “roaring” cats (lion, tiger, jaguar and leopard).

Purring.org is maintained by the (computational) linguist/phonetician/speech technologist/acoustician/musician (etc) Robert Eklund and information and sound files can be found at his other site http://ingressive.info or by clicking on the Wildlife button on his homepage.


Index




Robert Eklund records purring cheetah Caine

Elizabeth D. Duthie (behind the camera) and Robert Eklund record the cheetah
Caine at the Dell Cheetah Centre, Parys, South Africa in December 2010.
Note that a film clip is found on YouTube or below.

1 A purring primer
2 Scientific papers
  2.1  Fonetik 2015
  2.2  Fonetik 2013
  2.3  Fonetik 2012
  2.4  Fonetik 2011
  2.5  Fonetik 2010
3 Media interviews
  3.1  Press
  3.2  Radio
  3.3  TV
  3.4  Web
4 Purring animals
  4.1  Cheetah
  4.2  Serval
  4.3  Genet
5 Bibliography
6 Contact
7 Robert Eklund’s homepage
   

1 – A purring primer

The following text is basically lifted from Eklund, Peters & Duthie (2010), i.e. the paper presented at the Swedish Phonetics Conference at Lund University, 2–4 June, 2010, and is consequently co-written with Gustav Peters and Elizabeth D. Duthie, i.e.


[52]

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).
In: Proceedings of Fonetik 2010, Lund University, 2–4 June 2010, Lund, Sweden, pp. 17–22.
[pdf]


The term ‘purring’ has been used liberally in the mammal vocalization literature, and an exhaustive review is given in Peters (2002). Using a definition of purring that continuous sound production must alternate between pulmonic egressive and ingressive airstream (and usually go on for minutes), Peters (2002) reached the conclusion that until then only ‘purring cats’ (Felidae) and two species of genets (Viverridae sensu stricto), Genetta tigrina, and most likely also Genetta genetta, had been documented to purr.

The subdivision of the Felidae, the cat family, 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 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 conception, enables them to roar but not to purr. On the other hand, the snow leopard (Uncia uncia, 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, there is no well-founded and unequivocal basis for a classification of the species in the family Felidae according to the absence/presence of purring and roaring, respectively, and differences in hyoid anatomy. Weissengruber et al. (2002) decidedly 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.

The current classification of the Felidae is based on molecular characteristics (Johnson et al., 2006; O’Brien & Johnson, 2007) and groups the clouded leopards (Neofelis nebulosa and N. diardi) – with completely ossified hyoids – together with the five cat species in which it is incompletely ossified.



2 – Scientific papers

This section serves as a companion to the scientific papers that I and my co-authors have published on felid purring. Besides the papers proper, data files – sounds and video –  are found, as well as additional material.



2.1 – Fonetik 2015

Below you find the paper presented at the Swedish Phonetics conference in Lund on 8 June 2015. Nota bene! This paper is very much tongue-in-cheek, and should not be taken seriously but rather as entertainment.


[72]

Eklund, Robert. 2015.
Grimaldi’s “Discovery of the Cat Language”: A theory in need of revival (or perhaps not?) In: Proceedings from Fonetik 2015. Working Papers 55/2015, 8–10 June 2015, Centre for Languages and Literature, General Linguistics/Phonetics, Lund University, Lund, Sweden, ISSN 0280-526X, pp. 27–30.
[pdf]



2.2 – Fonetik 2013

Below you find the paper presented at the Swedish Phonetics conference in Linköping on 12 June 2013.


[68]

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, ISBN 978-91-7519-582-7, eISBN 978-91-7519-579-7, ISSN 1403-2570, pp. 25–28.
[pdf]



 

Fonetik 2013 Plate 1 ieter Kemp & Robert Eklund Purring Recording Session

 
 

Plate 1 from the Fonetik 2013 paper. Cheetah breeder Pieter Kemp and Robert Eklund recording the male cheetah Mufasa at the Dell Cheetah Centre, Parys, South Africa.

 


 

Fonetik 2013 Figure 1 Mufasa Egressive and Ingressive Phases

 
 

Figure 1 from the Fonetik 2013 paper. Adult male cheetah Mufasa purring; Egressive and ingressive phases.

 


   
 

Film clip corresponding to Figure 1. The film clip shows egressive (breathing out) and ingressive (breathing in) purring phases produced by the male adult cheetah Mufasa. The voice-over during the first two phases is Robert Eklund saying out aloud the words “ut” (out) and “in” (in) with his hand on the cheetah’s chest in order to get an audio synchronization of egressive and ingressive breathing on the recording.

 


 

Fonetik 2013 Figure 2 Tippi Egressive Ingressive Phases

 
 

Figure 2 from the Fonetik 2013 paper. Subadult female cheetah Tippi purring; Egressive and ingressive phases.

 


2.3 – Fonetik 2012

Below you find the paper presented at the Swedish Phonetics conference in Gothenburg (Göteborg) on the 30 May, 2012. The film clip is not identical to Figure in the paper, but instead includes six (instead of four) breathing phases.


[60]

Eklund, Robert, Gustav Peters, Florian Weise & Stuart Munro. 2012.
A comparative acoustic analysis of purring in four cheetahs.
In: Proceedings from FONETIK 2012.
Gothenburg, Sweden, May 30–June 1, 2012, pp. 37–40.
[pdf]


   
 

Film clip illustrating the relative amplitude between pulmonic egressive (exhalation) and pulmonic ingressive (inhalation) phases in cheetah purring. Six phases are shown:
egressive–ingressive–egressive–ingressive–egressive–ingressive

 


2.4 – Fonetik 2011

The following video clips and sound files served as the basis for the Schötz & Eklund (2011) paper presented at the Swedish Phonetics Conference held at the Royal Institute of Technology, Stockholm, Sweden, 8–10 June, 2011. The paper can be downloaded below.

Observe that all film clips are available in high-definition, full-screen format.


[57]

Schötz, Susanne & Robert Eklund. 2011.
A comparative acoustic analysis of purring in four cats.
In: Quarterly Progress and Status Report TMH-QPSR, Volume 51, 2011. Proceedings from Fonetik 2011.
Royal Institute of Technology, Stockholm, Sweden, 8–10 June 2010, pp. 9–12.
[pdf]


Domestic cat recording sessions

Short excerpts from the recording sessions with the four domestic cats Donna, Rocky, Turbo and Vincent. Recorded by Susanne Schötz in her home (in Sweden). The recording dates are given in the film clips.

Please observe that all four film clips can be expanded to high-definition full-screen viewing.


  Donna   Rocky  
     

  Turbo   Vincent  
     

Domestic cat sound files

Below you find sound files of purring produced by the four domestic cats Donna, Rocky, Turbo and Vincent (as shown in the videos above).

Donna [mp3]
Rocky [mp3]
Turbo [mp3]
Vincent [mp3]



2.5 – Fonetik 2010

The following film clips and images were presented at the Swedish Phonetics Conference at Lund University, Lund, Sweden, 2 4 June, 2010. They are also partly included in Eklund, Peters & Duthie (2010), i.e. the paper published in the Conference Proceedings.

Below you find streaming film clips and high-resolution images of the figures in the paper, which can be downloaded below. Observe that all film clips are available in high-definition, full-screen format.


[52]

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)
.
In: Proceedings of Fonetik 2010, Lund University, 2–4 June 2010, Lund, Sweden, pp. 17–22.
[pdf]


Cheetah recording session

Short excerpt from the recording session with the (constantly) purring cheetah Caine. Recorded by camera operator Elizabeth D. Duthie and microphone operator, linguist Robert Eklund. Recording date: 5 December, 2009, at the Dell Cheetah Centre, Parys, South Africa.


 

Waveform and spectrogram analysis of a purring cheetah

A short film clip showing four phases of cheetah purring, clearly showing the difference between egressive (out-breathing) and ingressive (in-breathing) phases from an acoustic point of view. The phases shown are (in order): egressive–ingressive–egressive–ingressive.


 

Waveform and spectrogram analysis of a purring domestic cat

A short film clip showing six phases of domestic cat purring, clearly showing the similarity between egressive (out-breathing) and ingressive (in-breathing) phases from an acoustic point of view (especially compared to the cheetah). The phases shown are (in order): egressive–ingressive–egressive–ingressive–egressive–ingressive.


 

Waveform transitions egressive–ingressive phases in purring cheetah and domestic cat

A short film clip of waveforms showing phase transitions from egressive (out-breathing) to ingressive (in-breathing) phases in a purring cheetah (top window) and a purring domestic cat purring (bottom window). Not ‘stereo effect’ at the end of the clip.


 

Image files of waveform and spectrogram analyses

Below you find high-resolution image files corresponding to some of the film clips above. Click on the files, and high-definition images will open in new tab or window. Please observe that the spectrogram images below also include the first four formants, unlike the figures presented in Eklund, Peters & Duthie (2010).

 

Waveform and spectrogram of purring cheetah

 
 

Waveform and spectrogram of purring domestic cat

 
 

Waveform and spectrogram of purring domestic cat

 

Frequency ranges of purring in a cheetah and a domestic cat

Below you find the observed frequency ranges of the purring cheetah and the purring domestic cat described in Eklund, Peters & Duthie (2010), mapped onto an extended piano keyboard (the greyish octave to the left does not exist on modern pianos, but is added to the keyboard). The green colour indicates the frequency range of the purring, and the completely coloured key represents the mean value of the purring.

 

Frequency range of purring in a cheetah

 
 

Frequency range of purring in a domestic cat

 


3 – Media interviews



3.1 – Press

On 5 April 2014 I was interviewed in Östgöta Correspondenten (web name Corren.se on the mystery of purring. The link below will take you there. (Note that it is in Swedish.)

Vill lösa mysteriet med spinnande kattdjur
[Translation: Wants to solve the mystery of purring cats.]

The print version can be downloaded here (1.2 MB): [pdf]


Journalist John Nyzell and editor Tatjana Kontio interviewed me about purring and other felid vocalizations for an article which appeared in Våra Rovdjur, the official organ of the Swedish Carnivore Association (Svenska Rovdjursföreningen. The interview appeared in the no. 1 issue in March 2014 and can be downloaded below, by kind permission of everyone involved. Note that it is in Swedish.

Katten vad det låter! (8.7 MB)

[pdf]



3.2 – Radio

I appeared on the Swedish public broadcasting program P4 Morgon (“P4 Morning”) on Thursday, 14 March 2014, where the program hostess Cia Sivertsdotter interviewed me about felid purring and similar vocalizations in other mammals, including alleged purring in both tigers (a non-purring felid) and other mammals. The interview can be downloaded below.

P1 Morgon, 13 March 2014. (8.7 MB, 18:30 minutes.)

[mp3]


I appeared on the Swedish public broadcasting program Naturmorgon (“Nature Morning”) on Saturday, 26 March 2011, where the program hostess Lena Näslund interviewed me about felid purring and similar vocalizations in other mammals, including alleged purring in both tigers (a non-purring felid) and other mammals. The interview can be downloaded below. The beep sound indicates where a cut-edit has been made (in the original version I appeared twice, once in the first hour of the program, and a second time in the second hour of the program).

Naturmorgon, 26 March 2011. (6.5 MB, 13:55 minutes.)

[mp3]


I appeared on the Swedish public broadcasting program Språket (“The Language”) on Tuesday, 1 June 2010, where the program hostess Anna Lena Ringarp interviewed me about felid purring. The interview can be downloaded below. The beep sound indicates where a cut-edit has been made.

Språket, 1 June 2010. (3.5 MB, 3:43 minutes.)

[mp3]



3.3 – TV

Interview by Henrik Lindberg, 24Corren

On 26 Mars 2014 I was interviewed by journalist Henrik Lindberg from 24Corren, in (and outside) my office at Linköping University, Linköping, Sweden. Made available by kind permission. (Note that the interview is in Swedish. Also note that I hadn’t slept for days and look awful!)


   

Watch the interview on YouTube.

Watch the interview on the 24Corren website:
http://www.corren.se/24corren/?clip=6866981



3.4 – Web

In February 2014 I was interviewed by Sofia Ström Bernad for the research and internal web pages at Linköing University. This resulted in two articles that can be accessed by clicking the links below. (Note that one of the pages is available in both Swedish and English.


Han kan lösa spinnandets gåta
(He may solve the riddle of purring)


Han ska lösa spinnandets gåta
in Swedish, or
Solving the mystery of purring
in English.


Please note that I don’t expect to solve the riddle of purring. I just enjoy studying it.



4 – Purring animals

Below you find additional sounds files of purring animals, including another cheetah, a purring serval and also a purring genet.



4.1 – Cheetah

The following recording of a purring cheetah also appears on Robert Eklund’s websites devoted to ingressive speech and phonation, i.e. http://ingressivespeech.info/, and (actually the same exact site) http://ingressive.info/. Additional information on wildlife-related issues, as well as wildlife pictures can also be found in the Wildlife section (click on the ‘Wildlife’ button) on Robert Eklund’s homepage: http://roberteklund.info/.


Purring cheetah

[mp3]

Cheetah 1


Recorded at the
Daniel Cheetah Breeding Farm
in South Africa,
29 November 2008

Purring elicited by
Robert Eklund

Cheetah 3

Cheetah 2

Cheetah 4



4.2 – Serval

The following recording of a purring serval also appears on Robert Eklund’s websites devoted to ingressive speech and phonation, i.e. http://ingressivespeech.info/, and (actually the same exact site) http://ingressive.info/. Additional information on wildlife-related issues, as well as wildlife pictures can also be found in the Wildlife section (click on the ‘Wildlife’ button) on Robert Eklund’s homepage: http://roberteklund.info/.


Purring serval

[mp3]

Serval 01



Recorded at the
Tenikwa Wildlife
Awareness Center

in South Africa,
25 November 2008

Purring elicited by
Miriam Oldenburg

Serval 02

Serval 02

Serval 04



4.3 – Genet

Since the only know example of a non-felid purring is the genet, a sound files is provided below. As is the case with the purring cheetah and the purring serval above, the following recording of a purring genet also appears on Robert Eklund’s websites devoted to ingressive speech and phonation, i.e. http://ingressivespeech.info/, and (actually the same exact site) http://ingressive.info/. Additional information on wildlife-related issues, as well as wildlife pictures can also be found in the Wildlife section (click on the ‘Wildlife’ button) on Robert Eklund’s homepage: http://roberteklund.info/.


Purring Genetta tigrina

[mp3]

Recording provided by
Dr Gustav Peters
at the
Forschungsmuseum Koenig
and with the kind permission of
Dr Chris Wemmer
who made the recording and
took the photo of the genet.

Dr Wemmer has a blog here.

Genetta tigrina

Reference

Christen M. Wemmer. 1977.
Comparative Ethology of the Large-spotted Genet
(
Genetta tigrina)
and Some Related Viverrids
.
Smithsonian Contributions
to Zoology, no. 239
Washington:
Smithsonian Institution Press.



5 – Bibliography

Depending on the approach, the literature on purring is either surprisingly meager, or replete with scientific mentions. While several papers on various species of felids do include mentions of “purring” among the various vocalizations pertaining to a particular species of cat, very few papers are devoted to purring proper. Below I will try to list works that belong to the latter category, while other papers that simply mention purring “in passing” will be added intermittently.

Note that this bibliography only includes scientific publications that has been published in journals on conference proceedings. This means that several sources are not included, e.g. articles in newspapers and similar. Also note that some of the papers below argue in favor of theories that have either been proven wrong (e.g. McCuiston, 1966) or have yet not been supported in any direct way by direct data or analysis (e.g. von Muggenthaler, 2001).

There are several books on felids/wild cats available, ranging from very introductory ones (aimed at children) to extremely exhaustive, scientific surveys (e.g. Sunquist & Sunquist (2002), as well as books devoted to e.g. cheetahs. I have included several of these in the listing below.


Bard, Philip. 1934.
   On Emotional Expression After Decortication With Some Remarks On Certain Theoretical Views
   Psychological Review, vol. 41, pp. 424–449, see p. 445.
Bazett, G. C. & W. G. Penfield. 1922.
   A Study of the Sherrington Decerebrate Animal in the Chronic as well as the Acute Condition
   Brain: A Journal of Neurology, vol. 45, pp. 185–265.
Beaver, Bonnie V. 1983.
   PURR-FECT communication
   Beastly Behavior, vol. 78, p. 41.
Becker, John E. 2010.
   Frenemies For Life. Cheetahs and Anatolian Shepherd Dogs
   Delaware, OH: Columbus Zoological Park Association.
Blacklock, Glenn A. 1972.
   A Cat’s Purr... On Purpose?
   Cat Fancy, vol. 16, pp. 20–41.
Bradshaw, John & Charlotte Cameron-Beaumont. 1998 (2nd edition in 2000).
   The signalling repertoire of the domestic cat and its undomestic relatives
   In: Dennis C. Turner & Patrick Bateson (eds.): The Domestic Cat. The biology of its behavior.
   Cambridge: Cambridge University Press,  ch. 5, pp. 93–21.
Brown, Kenneth A., Jennifer S. Buchwald, Judith R. Johnson & Dennis J. Mikolich. 1978.
   Vocalization in the Cat and Kitten
   Developmental Psychobiology, vol. 11, no. 6, pp. 559–570.
Denis, Armand. 1964.
   Cats of the World
   Science, vol. 144, pp. 555–556.
Dewson, James H. 1964.
   Speech Sound Discrimination by Cats
   London: Constable pp. 23–24.
Eklund, Robert. 2015.
   Grimaldi’s “Discovery of the Cat Language”: A theory in need of revival (or perhaps not?)
   Proceedings from Fonetik 2015. Working Papers 55/2015, 8–10 June 2015,
   Centre for Languages and Literature, General Linguistics/Phonetics, Lund University, Lund, Sweden,
   ISSN 0280-526X, pp. 27–30
Eklund, Robert & Gustav Peters. 2013.
   A comparative acoustic analysis of purring in juvenile, subadult and adult cheetahs.
   Proceedings of Fonetik 2013, the XXVIth Swedish Phonetics Conference, Studies in Language and Culture, no. 21,
   ISBN 978-91-7519-582-7, eISBN 978-91-7519-579-7, ISSN 1403-2570, pp. 25–28.
Eklund, Robert, Gustav Peters, Florian Weise & Stuart Munro. 2012.
   A comparative acoustic analysis of purring in four cheetahs
   Proceedings of Fonetik 2012, Gothenburg University, May 30–June 1, 2012, Göteborg, Sweden, pp. 41–44.
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, Lund University, 2–4 June 2010, Lund, Sweden, pp. 17–22.
Eldredge, Debra M., Delbert G. Carlson & Liisa D. Carlson. 2008 (third edition).
   A Cat Owner’s Home Veterinary Handbook
   Hoboken, New Jersey: Howell Book House.
Frazer Sissom, Dawn E., D. A. Rice & G. Peters. 1991.
   How cats purr
   Journal of Zoology, vol. 223,pp. 67–98.
Gibbs, E. L. & F. A. Gibbs. 1936.
   A Purring Center In The Cat’s Brain
   The Journal of Comparative Neurology, vol. 64, pp. 209–211.
Haskins, Ron. 1979.
   A casual analysis of kitten vocalization: an observational and experimental study
   Animal Behavior, vol. 27 pp. 726–736.
Hast, M. H. 1989.
   The larynx of roaring and non-roaring cats
   Journal of Anatomy, vol. 163 pp. 117–121.
Heffner, Rickye S. & Henry S. Heffner. 1985.
   Hearing range of the domestic cat
   Hearing Research, vol. 19, pp. 85–88.
Hemmer, Helmut. 1972.
   Uncia uncia
   Mammalian Species, no. 20, pp. 1–5.
Hussel, Lothar. 1949.
   Beitrag zur Physiologie des Schnurrens der Hauskatze
   PhD thesis, Veterinär-Medizinischen Fakultät der Universität Leipzig.
Härtel, Renate. 1975.
   Zur Struktur und Funktion akustischer Signale im Pflegesystem der Hauskatze (Felis catus L.)
   Biologisches Zentralblatt, vol. 94,pp. 187–204.
Johnson, Warren E. Eduardo Eizirik, Jill Pecon-Slattery, William J. Murphy, Agostinho Antunes, Emma
   Teeling & Stephen J. O’Brien. 2006.
   The Late Miocene Radiation of Modern Felidae: A Genetic Assessment
   Science, vol. 311, pp. 73–77.
Kirchner, John A. 1993.
   The Vertebrate Larynx: Adaptations and Aberrations
   The Laryngoscope, vol. 103, issue 10,  pp. 1197–1201.
Kitchener, Andrew C., Blaire Van Valkenburgh & Nobuyuki Yamaguchi. 2010.
   Felid form and function
   In: David Macdonald & Andrew Loveridge (eds.), Biology and conservation of wild felids,
   Oxford: Oxford University Press, chapter 3, pp. 86–106.
Kirkwood, P. A., T. A. Sears, D. Stagg & R. H. Westgaard. 1987.
   Intercostal muscles and purring in the cat: the influence of afferent inputs
   Brain Research, vol. 405, pp. 187–191.
Leyhausen, Paul. 1956.
   Über die unterscheidliche Entwicklung einiger Verhaltensweisen bei den Feliden
   Säugetierkundliche Mitteilungen, vol. 4, pp. 123–125.
Luschekin, Vitali S. & Kira V. Shuelikina. 1989.
   Some Sensorv Determinants of Home Orientation in Kittens
   Developmental Psychobiology, vol. 22, no. 6, pp. 601–616.
McLaughlin, Ronald Thomas. 1970.
   Aspects of the Biology of Cheetahs Acinonyx jubatus (Schreber) in Nairobi National Park
   MA Thesis, University of Nairobi, Kenya (299 pages).
McCuiston, W. R. 1966.
   FELINE PURRING and its dynamics
   Veterinary Medicine and Small Animal Clinician, vol. 61,pp. 562–566.
McComb, Karen, Anna M. Taylor, Christian Wilson & Benjamin D. Charlton. 2009.
   The cry embedded within the purr
   Current Biology, vol. 19, issue. 13, pp. R507–R508.
Mivart, George Jackson. 1881.
   The Cat. An Introduction to the Study of Backboned Animals, Especially Mammals
   New York: Charles Scribner’s Sons, p. 229.
Moelk, Mildred. 1944.
   Vocalizing in the House-Cat: A Phonetic and Functional Study
   The American Journal of Psychology, vol. 57, no. 2, pp. 184–205.
Morris, Desmond.
   Catwatching and Catlore
   London: Arrow Books Limited, pp. 15–17, 24–25.
Muggenthaler, Elisabeth von. 2001.
   The felid purr: A healing mechanism?
   Journal of the Acoustical Society of America, vol. 110, no. 5, pt. 2, p. 2666.
Müller, Gabriele. 2011.
   Miau: Katzensprache richtig deuten (Happy Cats)
   Stuttgart: Müller Rüschlikon Verlag.
Neff, Nancy A. & Joseph E. Hind. 1982.
   The Big Cats. The Paintings of Guy Coheleach
   New York: Abradale Press/Harry N. Abrams Inc., p. 20 et passim.
Neff, William D. & Joseph E. Hind. 1955.
   Auditory Thresholds of the Cat
   The Journal of the Acoustical Society of America, vol. 27, no. 3, pp. 480–483.
O’Brien, Stephen & Warren E. Johnson. 2007.
   The Evolution of Cats
   Scientific American, July 2007, pp. 68–75.
Owen, Richard. 1834/1835.
   On the Anatomy of the Cheetah, Felis jubata, Schreb.
   Transactions of the Zoological Society of London, vol. 1, pp. 129–137.
Peters, G. 2002.
   Purring and similar vocalizations in mammals
   Mammal Review, vol. 32, no. 4, pp. 245–271.
Peters, Gustav. 1981.
   Das Schnurren der Katzen
   Säugetierkundliche Mitteilungen, vol. 29, pp. 30–37.
Peters, Gustav, Megan Owen & Lynn Rogers. 2007.
   Humming in bears: a peculiar sustained mammalian vocalization
   Acta Theriologica, vol. 52, no. 4, pp. 379–389.
Peters, Gustav & Barbara A. Tonkin-Leyhausen. 1999.
   Evolution of Acoustic Communication Signals of Mammals: Friendly Close-Range Vocalizations
    in Felidae (Carnivora)

   Journal of Mammalian Evolution, vol. 6, no. 2, pp. 129–159.
Peters, G. & M. H. Hast. 1994.
   Hyoid structure, laryngeal anatomy, and vocalization in felids (Mammalia: Carnivora: Felidae)
   Zeitschrift für Säugetierkunde, vol. 59, pp. 315–330.
Pocock, R. I. 1916.
   On the Hyoidean Apparatus of the Lion (F. leo) and Related Species of Felidæ
   The Annals and Magazine of Natural History, Including Zoology, Botany, and Geology,
   vol. 28, series 8, pp. 222–229.
Reschke, B. 1960.
   Untersuchungen zur Lautgebung der Feliden
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    During Experimental Separation and Reunion Trials

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   Entomological Review, vol. 80, Suppl. 2, pp. S368–S378.


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