Play fighting in wild spotted hyenas: like a bridge over the troubled water of a hierarchical society

Play fighting, the most iconic form of social play, has been hypothesized to serve multiple evolutionary roles as a function of the age of the players. Although widely practised by youngsters, in some mammal species this form of play can also be present in adults. Here, we aimed to test these hypotheses by looking at the play-fighting behaviour of spotted hyaenas, Crocuta crocuta, by analysing the behaviour across age classes. Spotted hyaenas live in fission–fusion societies characterized by a rigid, nepotistic system of dominance hierarchy. Yet, the species is also characterized by social flexibility, which is evident from the high levels of support, cooperative behaviours and alliances. All these social features make spotted hyaenas a valuable model to explore play fighting at every age. We found that both immature individuals and adults invested a comparable amount of time in playful activities and showed similar motivation in initiating and maintaining their playful interactions. By play fighting, immatures can improve their motor and physical skills as predicted by the motor training hypothesis and, in agreement with the social assessment hypothesis, adults can gain information on social partners with whom they will have to interact in the future. Finally, contrary to our expectations, we found that those playful interactions characterized by strong competition (measured via play asymmetry index) also had the longest durations independently from the age of the players involved. Owing to the absence of escalation into real fighting, both immatures and adults appear to be able to manage the playful sessions despite their unbalanced nature. All these findings suggest that play fighting in spotted hyaenas can function as a ‘safe social bridge’ navigating both immatures and adults into the real future competitive challenges of the clan.