Differences in dogs' and wolves' human-directed greeting behaviour: facial expressions, body language, and the problem of human biases.

Dogs and wolves communicate effectively with humans, yet differences in their human-directed facial expressions and the role of relationship strength in shaping these behaviours remain poorly understood. This study explored the facial expressions of human-socialized wolves and dogs when greeting a bonded or familiar human through a fence. We hypothesised that differences would arise due to the domestication process, shaped further by the strength of their relationship. Additionally considering the bidirectionality integral to greeting interactions, we explored whether humans show different facial displays toward dogs versus wolves, expecting stronger differences in less bonded human partners due to unconscious biases. There was little overall difference between wolves' and dogs' facial expressions. However, wolves mainly displayed attentive, forward-directed ears, whereas dogs exhibited more ear positions associated with ambivalence or submission, such as rotated and downward-pushed ears. Dogs spent more time in proximity, gazing and tail wagging towards the human than wolves while both species showed more displacement behaviours (paw lift, whining, yawn) with bonded than familiar human partners. Interestingly, humans displayed more frequent, intense, and positive facial expressions toward dogs than wolves, suggesting implicit biases in human attitudes that were only partially influenced by familiarity. These results highlight the complexity of (studying) human-animal interactions. To what extent dogs' submissive yet human-seeking behaviour is indeed species-specific, or rather results from biased human treatment during their life, and which specific mechanisms drove the likely bidirectional influence remains to be explored.