• yawn
• yawn contagion
• chimpanzees
• pan troglodytes
• sbadiglio
• contagio di sbadiglio

Yawn is operationally described as “a powerful gaping of the jaw with inspiration, a brief period of peak muscle contraction and a passive closure of the jaw with shorter expiration” and it is consistently found across all but few classes of vertebrates.
Thanks to many observational studies and experiments, spontaneous yawn and yawn contagion have been linked to empathy, group synchronization, anticipation, arousal maintenance and many other behaviours and traits linked to the necessities of living in a group, as well as different physiological and biological traits (e.g. a link between brain’s cortex size and yawn duration).
In chimpanzees (Pan troglodytes) spontaneous yawn and its contagion have been mainly studied in experimental settings or in observational studies outlining its role in emotional contagion, anticipation, arousal, social status. Such studies have been conducted in captive conditions where group composition and living conditions poorly reflects the counterpart found in the wild. We analyzed 205 hours of footages recorded over the span of three seasons at the Chimfunshi Wildlife Orphanage in Zambia where animals are kept in large groups that include individuals of all ages and both sexes for different age categories and are hosted in large enclosures where surface area and vegetation better reflect life in the wild.
Understanding how yawns are used in a species so closely related to us can help better understanding how this behaviour is modulated in our species as well, since there are some objective difficulties in studying yawn and yawn contagion in humans (e.g. in experimental settings humans tend to yawn less in front of researchers, probably due to cultural implications of yawns).
In this work we will focus on the ontogeny of yawns by analyzing whether and how spontaneous yawns (i.e. not triggered by yawn contagion) change during this species’ life history, their concomitance with other behaviours, and their occurrence with different contexts such as feeding and aggression.
Furthermore, we will analyze how yawn contagion is expressed, and what factors better predict a facilitation of yawn contagion. For this part, alongside with familiarity, relationship, context of the dyad where yawn contagion mostly happens, synchronized behaviour that follow the event, we will also use ChimpFACS (Chimpanzee Facial Action Coding System), a tool to operationally and objectively describe the facial muscles (grouped in AU, Action Units) and other features involved in different yawns, to identify (if present) different morphologies of yawns and their possibly different involvement in yawn contagion.