Unravelling canine diplomacy: the social function of domestic dogs' visual displays

This thesis examines the role and communicative function of visual displays and facial expressions in domestic dogs (Canis lupus familiaris). Through five empirical studies, it examines how subtle visual cues contribute to social interactions within and between species, and how these behaviours are influenced by social bonds, morphology, and life experience. One set of studies focuses on eye-blinking. Dogs exposed to videos of conspecifics blinking increased their own blink rate, providing the first experimental evidence that blinking serves as a socially responsive signal in dog–dog communication. Extending these findings to interspecific interactions, it was found that dogs also showed higher blink rates towards their owners, which implies that attachment modulates responsiveness to visual cues. Further comparative research involving pet dogs, alongside hand-raised wolves and pack-dogs raised under identical conditions, revealed that social bonding enhances sensitivity specifically to human eye-blinking. By controlling for environmental factors, these findings show that the quality of social relationships and life experience, rather than species alone, shape responsiveness to this visual cue in canids. Additional studies examined facial expressions in relation to morphology and social context. While overall communicative abilities did not differ between brachycephalic and mesocephalic dogs, mesocephalic individuals adjusted their visual displays depending on the partner’s morphotype, suggesting perceptual and expressive constraints shaped by the extreme facial structure of brachycephalic dogs. Using an adapted Still-Face Paradigm, dogs displayed richer and more persistent visual displays toward their owners than towards familiar humans, emphasizing the role of attachment in interspecific communicative strategies. Together, these studies highlight the significance of even the subtlest of a dog's facial movements in its social behaviour. This research contributes to our overall understanding of how domestic dogs use visual communication, highlighting the role of factors like morphology, life experience and social bonds in shaping how dogs perceive and respond to both conspecifics and humans.