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A comparison of facial expression properties in five hylobatid species

Research output: Contribution to journalArticlepeer-review

  • Linda Scheider
  • Katja Liebal
  • Leonardo Ona
  • Anne Burrows
  • Bridget Waller
Little is known about facial communication of lesser apes (family Hylobatidae) and how their facial expressions (and use of) relate to social organization. We investigated facial expressions (defined as combinations of facial movements) in social interactions of mated pairs in five different hylobatid species belonging to three different genera using a recently developed objective coding system, the Facial Action Coding System for hylobatid species (GibbonFACS). We described three important properties of their facial expressions and compared them between genera. First, we compared the rate of facial expressions, which was defined as the number of facial expressions per units of time. Second, we compared their repertoire size, defined as the number of different types of facial expressions used, independent of their frequency. Third, we compared the diversity of expression, defined as the repertoire weighted by the rate of use for each type of facial expression. We observed a higher rate and diversity of facial expression, but no larger repertoire, in Symphalangus (siamangs) compared to Hylobates and Nomascus species. In line with previous research, these results suggest siamangs differ from other hylobatids in certain aspects of their social behavior. To investigate whether differences in facial expressions are linked to hylobatid socio-ecology, we used a Phylogenetic General Least Square (PGLS) regression analysis to correlate those properties with two social factors: group-size and level of monogamy. No relationship between the properties of facial expressions and these socio-ecological factors was found. One explanation could be that facial expressions in hylobatid species are subject to phylogenetic inertia and do not differ sufficiently between species to reveal correlations with factors such as group size and monogamy level.
Original languageEnglish
Pages (from-to)618-628
JournalAmerican Journal of Primatology
Volume76
Issue number7
Early online date3 Jan 2014
DOIs
Publication statusPublished - Jul 2014

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  • Gibbon MS_resub

    Rights statement: This is the accepted version of the following article: A comparison of facial expression properties in five hylobatid species. Scheider, L., Liebal, K., Ona, L., Burrows, A. & Waller, B. Jul 2014 In : American Journal of Primatology. 76, 7, p. 618-628, which has been published in final form at http://doi.wiley.com/10.1002/ajp.22255

    Accepted author manuscript (Post-print), 751 KB, PDF document

    Licence: CC BY-NC

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