Close human-wildlife interactions are rapidly growing, particularly due to wildlife tourism popularity. Using both laboratory and ecological observation studies we explored potential interspecies communication signalling mechanisms underpinning human-animal approach behaviour, which to date have been unclear. First impression ratings (n = 227) of Barbary macaques' social and health traits were related to the macaques' facial morphology and their observed behaviour supporting a shared facial signalling system in primates. These ratings significantly predicted intended approach to the macaques during hypothetical interactions. Finally, real-world interspecies proximity was observed and found to be best predicted by the interaction between human first impression perception and animal behaviour. Specifically, perceived macaque health in interaction with actual macaque dominance drives close interactions despite human proclivity to avoid dominant animals, raising safety concerns in interspecies interactions.A growing body of evidence suggests that we automatically form first impressions of people from their faces. These first impressions are made quickly 1 , non-consciously 2 , and incidentally without instruction 3 . These first impression judgements have been shown to influence people's behaviour toward an individual, determining the initiation of positive or negative interactions 4 . For instance, dominance is considered to be a cue of a person's intentions, and a dominant person could be considered as a potential threat 5 . Although the accuracy of first impression judgements has been largely debated 5-7 , previous studies have shown that first impressions of survival-related traits, e.g. dominance, were more accurate and consistent than more subtle characteristics such as intelligence, suggesting a potential evolutionary advantage of accurate first impression judgements. First impressions are important in interactions as they allow for the prediction of future behaviour 8 , which, if these judgements are inaccurate, could lead humans to put themselves at risk. However, to date, little is known about how humans make judgements of whether and how to interact with individual non-human animals (hereafter animals), and whether these judgements are accurate.It has been suggested that humans and non-human primates (hereafter primates) have a shared personality facial signalling system, and that both species could use first impression judgements to accurately assess other primate species' social and health traits 9 . For example, naïve participants have been shown to accurately rate extraversion social traits such as dominance in chimpanzees (Pan troglodytes) from static, neutral faces when compared to personality ratings from the chimpanzees' keepers 9,10 . Japanese and rhesus macaques (Macaca fuscata & Macaca mulatta) have also been shown to have a visual attentional preference for 'trustworthy' human faces 11 . Indeed, morphometric measures of facial structure such as the facial width to height ratio (fWHR) has been e...