Variation and context of yawns in captive chimpanzees (Pan troglodytes)
Article first published online: 11 DEC 2009
© 2009 Wiley-Liss, Inc.
American Journal of Primatology
Volume 72, Issue 3, pages 262–269, March 2010
How to Cite
Vick, S.-J. and Paukner, A. (2010), Variation and context of yawns in captive chimpanzees (Pan troglodytes). Am. J. Primatol., 72: 262–269. doi: 10.1002/ajp.20781
- Issue published online: 25 JAN 2010
- Article first published online: 11 DEC 2009
- Manuscript Accepted: 11 NOV 2009
- Manuscript Revised: 4 NOV 2009
- Manuscript Received: 7 SEP 2009
- Royal Zoological Society of Scotland (RZSS)
- Amercian Society of Primatology's Principles
- facial expression
Primate yawns are usually categorized according to context (e.g. as a threat, anxious, or rest yawn), but there has been little consideration of whether these yawns are best regarded as a unitary behavior that only differs with respect to the context in which it is observed. This study examined the context and precise morphology of yawns in a group of 11 captive chimpanzees. Focal video sampling was used to describe the morphology and intensity of 124 yawns using ChimpFACS, a system for coding facial movements. Two distinct forms of yawn were identified, a full yawn and a yawn which is modified by additional actions that reduce the mouth aperture. These modified yawns may indicate some degree of voluntary control over facial movement in chimpanzees and, consequently, multiple functions of yawning according to context. To assess context effects, mean activity levels (resting, locomotion, and grooming) and scratching rates were compared one minute before and after each yawn. Locomotion was significantly increased following both types of yawn, whereas scratching rates significantly increased following modified yawns but decreased following full yawns. In terms of individual differences, males did not yawn more than females, although male yawns were of higher intensity, both in the degree of mouth opening and in the amount of associated head movement. These data indicate that yawning is associated with a change in activity levels in chimpanzees, but only modified yawns may be related to increased arousal. Different types of yawn can therefore be differentiated at the morphological level as well as context level. Am. J. Primatol. 72:262–269, 2010. © 2009 Wiley-Liss, Inc.