Vinny, my Brittany, yawns a lot. He yawns first thing in the morning when he rises, in the evening when he is tired, and many times in between. We notice this because Vinny emits an adorable little squeaky sound whenever he launches a particularly wide and emotive yawn. We also know that Vinny seems to be highly susceptible to contagious yawning. If Mike or I or one of the other dogs yawn when we are close by, Vinny immediately joins in.
Recently, I was delighted to find a series of research studies examining the phenomenon of yawning in dogs and their people. The primary objectives of these studies were to determine if dog yawning, traditionally believed to be a mild stress response, is in actuality (or additionally) a reflection of social contagion and empathy.
Background information: Contagious yawning is a well-established phenomenon in humans. Not only are most of us easily induced to open wide when someone nearby emits a yawn, there is evidence that even just hearing a yawn noise or watching others yawning on a video are sufficient to trigger a yawn response. (Indeed, I would venture that simply reading the previous two sentences, in which the word “yawn” occurs six times, caused more than a few readers to……yawn).
There are several theories that attempt to explain why yawning is socially contagious. At the simplest cognitive level, group yawning may just reflect unconscious mimicry, a form of priming (see “The Steve Series” for a discussion of priming in dogs). This is the most parsimonious view as it does not require emotional attachment between the yawner and the “yawnee” and does not require the ability to empathize (or have a “theory of mind”). Alternate theories place contagious yawning somewhat higher on the social cognition scale and suggest that it represents an involuntary empathic response. In other words, people yawn when others do because they feel the same (i.e. empathize). According to this view, people should be more likely to yawn in response to others who they know well and have an emotional bond with than when they are with unfamiliar yawners. In recent years, data show that this is indeed true. Additional studies showing that people who score highly on psychological tests of empathy are more susceptible to contagious yawning have tipped the evidence scale towards the empathy theory (at least for people).
What about dogs? Although spontaneous yawning occurs in many mammals, contagious yawning has only been described in humans, chimpanzees, and in recent years – in dogs. Studies with dogs have asked three primary types of questions:
- Do dogs exhibit cross-species contagious yawning? In other words, does seeing a human yawn increase the likelihood that a dog will respond with a yawn?
- If it does occur, is it a type of empathic response? Are dogs more likely to yawn in response to someone they know and share an emotional bond with than they are in response to a stranger? If so, does contagious yawning have a communication function?
- And, a related question that is of interest to most trainers – May contagious (or spontaneous) yawning be simply a stress response that occurs during times of low or moderate anxiety? If so, is there a contagious component to it?
The Studies: The first published study of dog yawns appeared in 2008 in a paper entitled “Dogs Catch Human Yawns” (1). The researchers studied a group of 29 dogs and found that 21 of the dogs (72 %) demonstrated contagious yawning when sitting near an unfamiliar (yawning) person. The control group (eye contact plus non-yawning mouth movements) elicited zero yawns. This was pretty impressive, seeing that rates reported in humans range between 45 and 60 % and chimps come in at a paltry 33%. Although this study demonstrated yawn contagion, the design of the study did not allow the researchers to determine if the dogs were yawning as an expression of empathy or as a stress/anxiety response. Other researchers decided to study this further:
- Nope, ain’t happenin': A 2011 study compared yawn rates in dogs who were exposed to the yawns of either their owner, a stranger, or another dog (2). They also compared pet dogs living in homes with rescue dogs living in a shelter. Although they saw a bit of yawning (~ 26 percent of dogs), the rates did not differ significantly from control rates for any of these conditions. These researchers concluded that they found no evidence for empathy-based contagious yawning in dogs.
- Listen……there it is! This study took a different approach; they recorded the sound of yawning in 29 dog owners and then played these recordings back to each owner’s respective dog (3). The dogs were also exposed to the yawn sounds of an unfamiliar person and to familiar/unfamiliar non-yawn sounds (controls). Hearing the sound of yawning caused a response in 41 percent of the dogs and the sound of a familiar yawn elicited significantly more yawns than did the sound of an unfamiliar yawn. (Additional analysis of the data collected in this study suggested that stress-induced yawning was not an underlying cause of dog yawning, lending support for the social (empathy-based) theory ).
- I yawn for you: This 2013 study was specifically designed to test whether contagious yawning in dogs was a result of stress or if it reflected an empathic response (5). The researchers monitored dogs’ heart rates during each condition as a measure of physiological stress. Testing 25 dogs, they found that dogs did indeed demonstrate contagious yawning, that dogs yawned significantly more frequently in response to their owner than in response to an unfamiliar person, and that heart rates did not increase significantly during the experiment. Their results lend support to the hypothesis that dogs show contagious yawning with humans and that this behavior is socially modulated (i.e. empathy-based) rather than stress-based.
- But wait……do dogs also stress yawn contagiously? The most recent study, published in 2014, shows just how complicated the dog yawning story may actually be (6). Changing things up a bit, this group of researchers worked with a group of 60 shelter dogs and exposed them to a yawning (unfamiliar) experimenter. They measured both yawn responses and salivary cortisol levels, which like heart rate are expected to rise during periods of physiological stress. Contagious yawning in the shelter dogs occurred in only 12 (20 %) of the dogs, but interestingly, it was those dogs (the yawners) whose cortisol levels were increased. These results suggest that stress yawns can also occur contagiously.
Take Away for Dog Folks: Taken together, the results of these studies suggest that yawning in dogs may be context-specific, having different functions depending upon setting and situation. Similar to several other species, dogs do appear to yawn during periods of mild stress, possibly as a displacement behavior. In these cases, the yawn is accompanied by other communicative signs of tension such as a lowered body posture, panting, pacing or whining. [Note: While some posit that dogs yawn as a signal to "calm" other dogs or people, there is no empirical evidence to support this belief]. The data in these studies suggest that a stress yawn may also occur “contagiously” when faced with an unknown person in a new setting, perhaps as a result of the person (or her yawns) causing an increase in tension in the dog. Conversely, contagious yawning that occurs in a relaxed and happy dog, typically in response to a familiar person, may signify a type of social communication that reveals some level of empathic response. In those cases, what exactly is being communicated (“I’m tired too” or “This TV show is boring; can we please turn Lassie on”, or “Let’s go for ice cream!”) is still open to debate.
- Joly-Mascheroni RM, Senju A, Shephred AJ. Dogs catch human yawns. Biology Letters 2008;4:446-448.
- O’Hara SJ, Reeve AV. A test of the yawning contagion and emotional connectedness hypothesis in dogs, Canis familiaris. Animal Behaviour 2011;81:335-340.
- Silva K, Bessa J, Sousa L. Auditory contagious yawning in domestic dogs (Canis familiaris): first evidence for social modulation. Animal Cognition 2012;15:721-724.
- Silva K, Bessa J, deSousa L. Familiarity-connected or stress-based contagious yawning in domestic dogs (Canis familiaris)? Some additional data. Animal Cognition 2013;16:1007-1009.
- Romero T, Konno A, Hasegawa T. Familiarity bias and physiological responses in contagious yawning by dogs support link to empathy. PLoS ONE 2013:8(8):e71365.
- Buttner AP, Strasser R. Contagious yawning, social cognition, and arousal: An investigation of the processes underlying shelter dogs’ responses to human yawns. Animal Cognition 2014;17:95-104