Analysis of the intraspecific visual communication in the domestic dog (Canis familiaris): A pilot study on the case of calming signals

Studying the signaling of domestic dogs is crucial to have a better understanding of this species. The aim of this study was to scientifically assess if the behaviors called calming signals have a communicative and a calming function (i.e., de-escalating the aggressive display in the other dog). Twenty-four dogs, 12 females and 12 males, acted as senders; they were observed for the display of the behaviors considered by Rugaas (2006) as calming signals (CSs). The behavior of each sender dog was analyzed during four 5-minute off-leash encounters, in which the dog met 4 different recipients, respectively: a familiar and an unfamiliar dog of the same sex; a familiar and an unfamiliar dog of the other sex. The display and trend of aggressive behaviors in recipient dogs was also analyzed. In total, 2,130 CSs were observed. Some behaviors were displayed more often than others, especially, head turning, licking nose, freezing, and turning away. It was statistically more likely that the CSs were sent while the 2 dogs were interacting rather than when there was no interaction (χ2 = 836.155; P < 0.001), suggesting these signals have a communicative role. The statistical analysis revealed that a higher number of signals were observed during meetings between unfamiliar dogs (χ2 = 108.721; P < 0.001). Head turning, nose licking, freezing, making him/herself smaller, and paw lifting were displayed by the sender statistically more frequently while interacting with unfamiliar dogs. Licking the other dog's mouth was more commonly directed toward familiar dogs. In total, 109 episodes of aggressive behaviors were displayed by the recipient dogs. Aggressive episodes were never preceded by the display of a calming signal from the other dog. In 67.0% of cases (N = 73), at least 1 CS was displayed by the sender dog after having received an aggressive behavior from the recipient. When CSs were displayed after an aggressive interaction, in 79.4% of cases (N = 58), there was a de-escalation in the aggressive display of the other dog. It was statistically less likely that the intensity of aggressive behaviors increased (5.5%/N = 4) or remained unvaried (15.1%/N = 11; χ2 = 13.17; P < 0.001). These findings suggest that these CSs indeed may have a role in social facilitation and preventing further aggressive behaviors.