The adaptive function of yawning is unclear, but yawning may serve a communicative purpose. Previous studies have suggested that contagious yawning is linked to empathy, and perhaps observed only in species with complex cognitive functioning.
Whether domestic dogs can exhibit yawn contagion in response to human yawns is debated. We investigated whether dogs’ susceptibility to yawning in response to a human is associated with their sensitivity to understanding human social cues. Shelter dogs were tested in yawn contagion trials and on the object choice task to determine if there is a link between their social cognitive capacities and contagious yawning. Salivary cortisol samples were taken to determine if yawning was the result of arousal rather than true contagion. Twenty-nine percent of the overall sample yawned more in the yawning trial than the control trial, which is consistent with more recent studies on yawn contagion in dogs.
Yawning was not related to dogs’ performance on the object choice task, but cortisol levels were associated with contagious yawning. Specifically, dogs that did exhibit yawn contagion had higher cortisol levels following the yawning trials, suggesting that these dogs were more physiologically aroused than dogs that did not yawn contagiously. Further, dogs that received the yawning condition first tended to have higher cortisol levels than dogs that received the control condition first.
These dogs also tended to yawn more in the yawning condition than the control, showing nearly significant levels of yawn contagion as a group. Given the trial order effects observed, human yawning may produce physiological arousal in some dogs, which results in contagious-like yawning in these dogs. Our findings suggest that contagious yawning in dogs may operate on some other mechanism than it does in more cognitively complex species. The arousal explanation supports the hypothesis that the underlying physiological and communicative function of yawning is to increase alertness and vigilance in the yawner and conspecifics and may imply interspecies communication, though the role of empathy is unclear.