Domestic dogs display calming signals more frequently towards unfamiliar rather than familiar dogs

Rugaas (1997) describes “calming signals” as certain dog behaviors that would allow subjects receiving them to calm, avoiding open aggression. The aim of the current research is to assess whether the display of the so-called “calming signals” differs according to the familiarity of dogs involved in the meeting. We studied 20 dogs (10 males and 10 females) who met conspecifics within an outdoor fence (5 x 5 m). In all of the encounters dogs were in pairs and off-leash, but both owners were present within the fence and instructed not to interact with the dogs. Subjects showing open aggression to dogs or humans were excluded for ethical reasons. Each dog met four conspecifics: a female and a male familiar dog, and a female and a male unfamiliar dog. Each 5-minute encounter was videorecorded from two different points and then analyzed to measure the total number of emissions of the signals. Examined signals were 21 of those suggested by Rugaas (1997): ‘turning head’, ‘looking elsewhere’, ‘half-closing eyes’, ‘turning on other's side or back’, ‘licking nose, freezing’, ‘moving slowly’, ‘play bow’, ‘sitting’, ‘sitting and turning on other's back’, ‘laying down (sternal decubitus)’, ‘yawning’, ‘sniffing the ground or wall’, ‘approaching the other dog curving’, ‘waving low tail’, ‘cowering’, ‘licking the other dog's mouth’, ‘blinking’, ‘smacking’, ‘raising a forelimb’ and ‘low urination’. We could not consider two signals listed by Rugaas (1997): ‘going between’, because dogs were only two in each meeting, and ‘pretending to ignore the other dog exists’, as the assessment may result too subjective. Analyzing videos, it was found that the total number of signals were more than doubled when the dogs met were unfamiliar (848 vs. 365). This suggests that facing an unknown subject is more challenging and needs clearer communication regarding intentions. Comparing the display of single behaviors between familiar and unfamiliar dogs, we observed a very similar trend for most behaviors, with a tendency to higher frequencies when dogs did not know each other. In particular, some signals were rarely or not displayed at all in both conditions (‘low urination', ‘blinking’, ‘smacking’, ‘licking others dog's muzzle’, ‘slow movements’, ‘play bow’, ‘sitting’, ‘sitting on other's side or back’, ‘sternal decubitus’, ‘yawning’, ‘curving’, ‘waving low tail’ and ‘raising a forelimb'). Some other signals were displayed nearly twice as often in case of unfamiliar dogs, even if overall frequencies were not high (‘sniffing ground or wall’: 28 vs. 18; ‘turning on other's side or back’: 43 vs. 26; ‘turning head’: 95 vs. 40; ‘licking nose’: 168 vs. 59), but differences were not statistically significant. ‘Looking elsewhere’ (265 vs. 166; χ2 = 21.938; p = 0.0001) and ‘freezing’ (135 vs. 20; χ2 = 24.027; p = 0.0001) were significantly more frequent in encounters between unfamiliar dogs. In conclusion, intraspecific communication in dogs seems to vary according to familiarity, the difference being more in degree rather than in kind. A higher number of calming signals (especially specific ones, such as ‘looking elsewhere’ and ‘freezing') are displayed when a dog meets an unfamiliar dog.