Welcome to AnimalFACS

Welcome to animalfacs.com, the home of all the scientific observational tools for identifying and coding facial movements in non-human species.

To date, seven systems have been adapted from the original Facial Action Coding System (FACS) used for humans, allowing the objective coding of facial movements in various species.

The development of species-specific anatomically based coding systems has facilitated within-species and cross-species comparisons of facial expression over recent years. 

The original FACS system

The investigation of human facial non-verbal communication has been greatly facilitated and standardised by the development of the Facial Action Coding System (FACS: Ekman et al., 2002; Ekman and Friesen, 1978). Prior to this, the human facial expression field was reliant on more subjective methods and did not have a systematic way to assess the muscular components of facial expression.

FACS identifies facial movements based on the underlying physiology and aims to identify individual muscle contractions, focussing not on the expression of emotions but on the production of spontaneous facial movements. For example, FACS is able to compare facial expressions objectively across individuals regardless of the inherent variability in the surface morphology of faces, e.g., bone structure, fatty deposits, skin texture, and individual muscle variations (Waller et al. 2007; Waller et al. 2008a). FACS can compare facial movements regardless of superficial individual differences in other aspects of facial anatomy, such as hair covering, facial coloration, bone structure, etc. This latter characteristic also makes FACS ideal for modification across species.

FACS uses numbers to refer to 33 facial muscle contractions (Action Units [AUs]) and 25 more general head/eye movements (Action Descriptors [ADs]). It presents each AU in terms of underlying musculature (location and direction of action), appearance changes (multiple cues for identifying AUs), reference for AUs (subtle differences between AU combinations), how to do the AU (voluntary production of AU in isolation), and intensity scoring for the AU (criteria for coding decisions).

A system adapted to 7 species



Chimpanzee Facial Action Coding System (ChimpFACS) is an observational, scientific tool to record and analyse facial expressions in chimpanzees. It was the first system to be adapted from the original one.



GibbonFACS is a modification of the original human FACS system (Ekman & Friesen 1978), for use with hylobatid species (gibbons and siamangs).


The Dog Facial Action Coding System (DogFACS) is a scientific observational tool for identifying and coding facial movements in dogs.



The Macaque Facial Action Coding System (MaqFACS) is a scientific observational tool for identifying and coding facial movements in rhesus macaques.



The Orangutan Facial Action Coding System (OrangFAC) is an observational tool for identifying and coding facial expressions in orangutans.


The Cat Facial Action Coding System (CatFACS) is a scientific observational tool for identifying and coding facial movements in cats.


The Equine Facial Action Coding System (EquiFACS) is a scientific observational tool for identifying and coding facial movements in domestic horse (Equus caballus).


Original FACS manual

  • Ekman, P. & Friesen, W.V. (1978). Facial action coding system. California: Consulting Psychology Press.
  • Ekman, P., Friesen, W.V. & Hager, J.C. (2002). Facial action coding system. Salt Lake City: Research Nexus.

Adapted FACS manuals

  • ChimpFACS: Vick, S.J., Waller, B.M., Parr, L.A., Smith Pasaqualini, M.C. & Bard, K.A. (2007). A cross-species comparison of facial morphology and movement in humans and chimpanzees using the facial action coding system (FACS). Journal of Nonverbal Behaviour, 31(1), 1-20. View article.
  • MaqFACS:  Parr, L.A., Waller, B.M., Burrows, A.M., Gothard, K.M. & Vick, S.J. (2010). MaqFACS: A muscle-based facial movement coding system for the macaque monkey. American Journal of Physical Anthropology, 143 (4), 625-630. View article.
  • GibbonFACSWaller B.M., Lembeck M., Kuchenbuch, P., Burrows, A.M., Liebal, K. (2012). GibbonFACS: A Muscle-Based Facial Movement Coding System for Hylobatids. International Journal of Primatology, 33 (4), 809-821. View article.
  • OrangFACS: Caeiro, C.C., Waller, B.M., Burrows, A.M., Zimmermann, E., Davila-Ross, M. (2013). OrangFACS: A muscle-based coding system for orangutan facial movements. International Journal of Primatology, 34 (1), 115-129. View article.
  • CatFACS: Caeiro, C.C., Burrows, A.M., Waller, B.M., 2017a. Development and application of CatFACS: Are human cat adopters influenced by cat facial expressions? Applied Animal Behaviour Science 189, 66–78. View article.
  • DogFACS: Waller, B.M., Peirce, K., Caeiro, C.C., Scheider, L., Burrows, A.M., McCune, S., & Kaminski, J. (2013). Paedomorphic facial expressions give dogs a selective advantage. PloS one, 8 (12), e82686. View article.
  • EquiFACSWathan, J., Burrows, A.M., Waller, B.M., McComb, K., 2015. EquiFACS: The Equine Facial Action Coding System. PLoS ONE 10, e0131738. View article.

Examples of research using the FACS systems

  • Burrows, A., Waller, B.M. & Parr, L.A. & Bonar, C.J. (2006). Muscles of facial expression in the chimpanzee (Pan troglodytes): Descriptive, comparative, and phylogenetic contexts. Journal of Anatomy, 208(2), 153-168. 
  • Friedman, H. (2007). Chimp facial action coding: an important forward brachiation in method. Journal of Nonverbal Behavior, 31, 21-22. (Editorial comment on Vick et al., 2007). 
  • Parr, L., Waller, B.M., Vick, S.J., (2007). New developments in understanding emotional facial signals in chimpanzees. Current direction in Psychological Science, 16, 117-122. 
  • Parr, L.A., Waller, B.M., Vick, S.J., Bard, K.A., 2007. Classifying chimpanzee facial expressions using muscle action. Emotion 7, 172–181.
  • Vick, S.-J., Waller, B.M., Parr, L.A., Smith Pasqualini, M., Bard, K., 2007. A Cross-species Comparison of Facial Morphology and Movement in Humans and Chimpanzees Using the Facial Action Coding System (FACS). Journal of Nonverbal Behavior 31, 1–20.
  • Waller BM, Bard KA, Vick SJ, Pasqualini MCS. 2007. Perceived differences between chimpanzee (Pan troglodytes) and human (Homo sapiens) facial expressions are related to emotional interpretation. Journal of Comparative Psychology 121:398–404
  • Parr, L.A., Waller, B.M., Heintz, M., 2008. Facial expression categorization by chimpanzees using standardized stimuli. Emotion 8, 216–231.
  • Waller, B. M., Parr, L. A., Gothard, K. M., Burrows, A. M., & Fuglevand, A. J. (2008a). 1995 Mapping the contribution of single muscles to facial movements in the Rhesus Macaque. Physiology & Behavior, 95, 93–100
  • Parr, L.A., Heintz, M., 2009. Facial expression recognition in rhesus monkeys, Macaca mulatta. Animal Behaviour 77, 1507–1513.
  • Bard, K. A., Gaspar, A. D., & Vick, S. J. (2011). Chimpanzee faces under the magnifying glass: Emerging methods reveal cross-species similarities and individuality. In Personality and temperament in nonhuman primates (pp. 193-231). Springer, New York, NY. 
  • Burrows, A.M., Diogo, R., Waller, B.M., Bonar, C.J., Liebal. K. (2011). Evolution of the Muscles of Facial Expression in a Monogamous Ape: Evaluating the Relative Influence of Ecological and Phylogenetic Factors in Hylobatids. The Anatomical Record, 294 (4), 645-663. 
  • Dobson, S.D., 2012. Coevolution of Facial Expression and Social Tolerance in Macaques. American Journal of Primatology 74, 229–235. https://doi.org/10.1002/ajp.21991
  • Liebal, K., Waller, B. M., Slocombe, K. E., & Burrows, A. M. (2013). Primate Communication: a multimodal approach. Cambridge University Press.
  • Waller, B.M., Peirce, K., Caeiro, C.C., Scheider, L., Burrows, A.M., McCune, S., Kaminski, J., 2013. Paedomorphic Facial Expressions Give Dogs a Selective Advantage. PLOS ONE 8, e82686. https://doi.org/10.1371/journal.pone.0082686
  • Liebal, K., Waller, B.M., Burrows, A.M., Slocombe, K.E., 2014. Primate communication: a multimodal approach. Cambridge University Press, Cambrige, UK.
  • Scheider, L., Liebal, K., Oña, L., Burrows, A.M., Waller, B.M., 2014. A comparison of facial expression properties in five hylobatid species. American Journal of Primatology 76,618–628.
  • Davila-Ross, M., Jesus, G., Osborne, J., Bard, K.A., 2015. Chimpanzees (Pan troglodytes) Produce the Same Types of ‘Laugh Faces’ when They Emit Laughter and when They Are Silent. PLOS ONE 10, e0127337. https://doi.org/10.1371/journal.pone.0127337
  • Micheletta, J., Whitehouse, J., Parr, L.A., Waller, B.M., 2015. Facial expression recognition in crested macaques (Macaca nigra). Animal Cognition 18, 985–990. https://doi.org/10.1007/s10071-015-0867-z
  • Waller, B.M., Caeiro, C.C., Davila-Ross, M., 2015. Orangutans modify facial displays depending on recipient attention. PeerJ 3, e827. https://doi.org/10.7717/peerj.827
  • Julle-Daniere, E., Micheletta, J., Whitehouse, J., Joly, M., Gass, C., Burrows, A. M., & Waller, B. M. (2015). MaqFACS (Macaque Facial Action Coding System) can be used to document facial movements in Barbary macaques (Macaca sylvanus). PeerJ3, e1248. https://doi.org/10.7717/peerj.1248

  • Scheider, L., Waller, B.M., Oña, L., Burrows, A.M., Liebal, K., 2016. Social Use of Facial Expressions in Hylobatids. PLOS ONE 11, e0151733. https://doi.org/10.1371/journal.pone.0151733
  • Caeiro, C.C., Burrows, A.M., Waller, B.M., 2017a. Development and application of CatFACS: Are human cat adopters influenced by cat facial expressions? Applied Animal Behaviour Science 189, 66–78. https://doi.org/10.1016/j.applanim.2017.01.005
  • Caeiro, C.C., Guo, K., Mills, D., 2017b. Dogs and humans respond to emotionally competent stimuli by producing different facial actions. Scientific Reports 7, 15525. https://doi.org/10.1038/s41598-017-15091-4
  • Kaminski, J., Hynds, J., Morris, P., Waller, B.M., 2017. Human attention affects facial expressions in domestic dogs. Scientific Reports 7, 12914. https://doi.org/10.1038/s41598-017-12781-x
  • Florkiewicz, B., Skollar, G., Reichard, U.H., 2018. Facial expressions and pair bonds in hylobatids. American Journal of Physical Anthropology 167, 108–123. https://doi.org/10.1002/ajpa.23608

Contact us

Psychology Department

University of Portsmouth

Portsmouth, UK

Copyright © All Rights Reserved