• Communication
• Behaviour
• Drills
• Contagoius yawning
• Spontaneus yawning
• Yawn

Spontaneous yawning is a widespread behaviour in vertebrates and specifically in primates. However, data on drills are not present in literature. In this work we aimed to study yawning behaviour in drills (Mandrillus leucophaeus). The data were collected from August through October 2020 at the Dvůr Králové Zoo, located in the Czech Republic where there is a colony of 12 individuals (7 males and 5 females). Several yawning morphologies have been identified in literature according to whether or not teeth are exposed during yawning. In our work we hypothesise that also in drills, two yawning morphologies are present: yawn with covered teeth (Y1) and yawn with uncovered teeth (Y2) and the first goal of our work was demonstrate that not only there is a macroscopic and qualitative difference between these two yawning morphologies but also a quantitative one and this was possible thanks to the use of MaqFACS. Assuming a clear distinction can be made between Y1 and Y2, we will verify whether some factors significantly influence the morphology of yawning. Specifically, the factors that we considered are: the sex of the yawner (male/female); the age of the yawner (juvenile/adult), duration of yawning; and finally the context: relax (animals in a relaxed situation e.g. resting, sleeping, grooming) or arousal (animals in a stressful situation e.g. animals involved in a conflict or threat). The results show that all males, not only the dominant one, yawn more and show mostly big yawns (Y2). Therefore it is not said that the morphology of yawning is linked only and strictly to the exposure of the canine, but it could be related to a factor of testosterone, which then affects all males of the group and not only the dominant.
We have also verified The State Changing Hypothesis, which predicts that if yawning is involved in behavioural transitions, the frequency of yawning should increase in coincidence of such transitions (from behaviour A to behaviour B).
Moreover our data suggest the presence of yawning contagion in drills. The frequency was quite low (25.81%), therefore it would be once again desirable to continue exploring this phenomenon in other groups of drills and by collecting more yawning events.