Let's Call A Truce…For Now: The Silent Bared-Teeth Face Expression in Mandrills (Mandrillus sphinx) During Baseline and Post-Conflict Conditions



The distinction between signals that are friendly and those that are non-aggressive but motivationally neutral (signals of benign intent, SBIs) has not often been well elucidated in the literature. Although both signals occur in similar contexts, friendly signals should be exchanged more often between animals with good relationships whereas SBIs should be more commonly exchanged between animals with poor or unpredictable relationships. The importance of this distinction is particularly salient in the post-conflict context, because the two different types of signals may have disparate distributions and functions. This study examines the nature of the silent bared-teeth face (SBTF) in captive mandrills (Mandrillus sphinx) both during baseline interactions and following aggressive conflicts. We report that the SBTF is most commonly exchanged between mandrills with high rates of agonism. In addition, the SBTF is the most common post-conflict signal exchanged, and the mandrills exchanging this signal after fighting also have poor relationships. We conclude that, although one must be careful in generalizing from studies of captive populations, the mandrill SBTF observed in this study is most accurately classified as a signal of benign intent, but not a truly friendly signal and discuss problems with interpreting post-conflict data without distinguishing between these types of signals.