• aggressive behaviour
• facial expressions
• play behaviour
• play fighting
• relaxed open mouth
• wolves

Play behaviour and agonistic behaviour are two essential elements in the daily life of social animals. Within social play, play-fighting is the most common and riskiest because it involves easily misunderstandable patterns recruited from agonistic behaviour. For this reason, communication is crucial in making the playful session rewarding for all the participants and several signals have undergone the process of ritualization to help informing the playful mood. One example is the relaxed open mouth display (ROM), which is, according to several authors, the ritualized version of the biting action. During agonistic encounters, escalation is preferentially avoidable due to the high risk of injuries. Animals can present several aggressive signals efficient in deterring the opponent, making communication central also in this scenario. The aim of this thesis is to compare visual signals, in particular the facial expressions used in the playful and the aggressive domains, in our model species, the social carnivore wolf (Canis lupus). Wolves are a valuable candidate for our investigation because besides being social they are very competitive, start engaging in play-fighting from a very early stage of life and keep playing as adults. On the other hand, wolves live in a hierarchical society and conflicts among individuals can occur often. Additionally, wolves present a wide range of facial expressions and heavily rely on visual communication during playful and aggressive encounters. In particular a motivational model of different facial expressions based on increasing fear and aggressiveness was proposed by Zimen (1971) that described the gradient of variability of wolves’ threatening displays. However, a quantitative description of these facial signals was still missing. Video and acoustic data were collected from the 2nd of October to the 5th of Nov 2021 in the ‘Belpark’ faunistic park in Spormaggiore (Trento, TN, Italy) on a colony of 10 captive grey wolves (Canis lupus lupus, 5 males and 5 females, all adults). Videos were analysed frame-by-frame with software Potplayer 1.7.21305. We scored several pieces of information during all the playful (N = 124) and aggressive (N = 277) sessions, including the identity of the individuals, the patterns they performed, the duration of the patterns and any other relevant behavioural cues. We analysed different facial expressions in both domains using the Facial Action Coding System (FACS). We performed a cluster analysis that helped us demonstrate the context-specificity of facial expressions. We found that playful facial expressions are exclusively performed in the playful domain and the threatening ones only occasionally occur during play fighting. We used the same approach to provide a quantitative description of the facial signals in both the playful and aggressive domains. Our results revealed the presence of two play faces, ROM and HalfROM, that are distinct from the biting action and present a more consistency in the recruitment of different muscular action units (AUs), supporting the hypothesis that these signals have undergone a process of ritualization. These signals were most frequently performed in anticipation of an offensive pattern, suggesting a metacommunicative function, similarly to what has been proposed for other social carnivores. For the aggressive signals, we were able to identify the elements composing the different facial displays and provide a quantitative description of the Zimen (1971) motivational model. We were also able to identity some morphological features that may play a key role during aggressive communication, such as the pink spot on the upper gum and the frowning of the brows. At last, based on the data collected we were also able to determine the hierarchical structure of our pack, that resembled a pyramidal one. We also investigated the possible functions of play fighting and real fighting by building different social networks based on their respective occurrence. These results will be useful for future investigations on the distinct usage of signals in the two domains.