What’s in a Yawn?
Canine body language is fascinating to both observe and to learn about, and there are many really good books and sites on the subject. You can find a great visual summary covering the basics designed by Sophia Yin and Lili Chan here as a free poster. The more you start watching your own dogs you’ll quickly come to realise that, ‘dog’ as a foreign language is a complex and by no means a fully explored and understood topic.
Yawning is one of the less well known parts of body language that you can might be able to catch your dog doing. Although both dogs and people yawn when they are tired, but we also yawn in other situations like when we are stressed or bored, and it seems that no-one has a particularly satisfactory answer as to physically why we do. Also anyone who has ever witnessed how yawns are passed from person to person knows that yawning can be highly contagious, try to see if you can spot your own dog yawning when you do – as yawns can also be passed from person to dog, adding a social dimension to yawning.
Have you seen your dog yawning when they are facing something daunting or stressed? In my household it’s Stig, my oldest dog also pictured above, who I notice yawns most. In most situations I interpret this not so much as stress we usually talk about it, which can be a precursor to aggression, but for him it seems to be a combination of being both excited and slightly uncertain as he usually yawns when the play between my other two dogs is getting little too strident. Zero, who is by nature more nervous, will however, yawn just before going for a walk when his harness is already on and we’re just about to go out of the door. For him the yawn suggests a different emotional state: anticipation and excitement. But the physical process behind both is a burst of adrenaline which is part of a fight or flight response preparing the dog for action and hence both Stig and Zero yawn but are saying different things.
Turid Rugass writes in her book ‘On Talking Terms with Dogs: Calming Signals’ that yawning is jut one among many ‘calming signals’ — used when a dog faces a potential threat such as a person bending over them, with the result of calming the other party, by indicating that the animal feels calm and not aggressive, and averting a potentially dangerous situation. In line with this are the uncertain or stress yawns that Stig shows. He is uncomfortable with the tension developing between the other dogs, that is clear, but is he yawning to calm the other dogs?
Brenda Aloff’s book ‘Canine Body Language – A Photographic Guide’ suggests that stress yawning is particularly common when the dog is under social pressure. Again, this is in line with Stig’s yawning, triggered by the behaviour of other dogs, and ties in nicely with the fact that yawns have a social element shown by their contagious nature.
When I was first learning about canine body language I accepted stress yawns at face value: they are obvious once you start looking for them. When your dog finds itself in a stressful situation, one of the ways they communicate this unease is by yawning. There is also scientific research that suggests that yawning helps to diffuse tension in dog-human social interactions, specifically a person yawning increases the tendency of a dog to look away from them, the dog is reducing the chances of eye contact and displaying a non threatening gesture (Buley, 2008). In my head one of the ways this communication translates to words is as that the person yawning says to the dog ‘I’m uneasy’ and the dog is replying ‘no need to worry about me, I don’t want to fight’. But then the yawn does not act as a calming signal, just a way of expressing that the dog is uneasy.
As I started thinking more about yawns and if they functioned as a way to calm either the dog yawning or the other dog in an interaction I just kept asking why? What physical purpose does it serve? It seems fair to say that yawning probably started as a physiological action which then became important in communication, akin to urination in dogs which also plays a role in communication through scent marking. So why do we yawn?
The first explanation I discovered was that as you draw a large breath as the first part of the yawn you are adding oxygen to your body. This seemed to make sense in terms of why it would occur when the dog is stressed, or in fact excited. Once a dog has entered a fight or flight condition they would need extra oxygen for either outcome. But this didn’t fit with why it would the yawn act to calm itself, another dog or diffuse the tension in a social situation? So I searched around a little more.
Assuming the physical processes are the same for both humans and dogs, we can borrow from human research, and it turns out that scientists have shown that reduced oxygen, or increased carbon dioxide, does not increase the rate of yawning (Provine et al., 1987). So, yawning is probably not be triggered by a need for oxygen, and therefore, it is hard to see why dogs entering a fight of flight response due to a stressful situation would yawn in order to increase oxygen levels.
Another potential reason for yawning is that it acts as a mechanism to regulate brain temperature (Gallup and Gallup, 2007). In turn this would act to boost or maintain alertness, fitting in well with the fact that both dogs and humans yawn when we are tired. The authors also potentially explain the contagion of yawns as a need for group alertness. The fact that anxiety can increase body temperature (even though it is a small effect), could then explain why this triggers yawning when a dog is anxious, it cools their brain and gives a boost to alertness when the dog may need it most. But this clearly can’t be the only reason we, or dogs yawn.
So, looking little deeper I came across research suggesting that the contagious nature of yawning is related to the level of empathy between the dog and person. Research has suggested that contagious yawning is not only related to how well the dog knows a person but also does not correspond to a change in a dog’s heart rate, which would rule out any stress (Romero et al., 2013). Therefore, these ‘social’ yawns may be slightly different to ‘stress’ yawns. An interesting note is that so far only humans, certain primates, wolves and dogs have been shown to exhibit contagious yawning, and I couldn’t find any references to dog to dog contagion of yawns, only human to dog transfer. It does seem likely that since wolves seem to pass yawns to each other dogs may be able to as well (Romero et al., 2014), so from now on I will be keeping an eye out!
The most interesting thread of research I found was a link between yawning and suppression of the sympathetic nervous system (Askenasay and Askenasay, 1996). The reason this is important is that the sympathetic nervous system is the part of your nervous system which controls your fight or flight response. So if yawning suppresses this, even in a small way it could actually be promoting calmness and relaxation in your dog, coming full circle back to yawning as a self-calming signal and communication of unease. When the dog feels uneasy or threatened but it is not a clear threat, the body keeps itself form overreacting by a gentle nudge towards calmness, a yawn.
Scientists will continue to investigate yawning as there are still many unanswered questions. Regardless of the ultimate physical reason that dogs are yawning — they are doing it and we should be aware of this as part of this continual dialogue our dogs’ body language expresses. As with any body language it needs to be seen in context and taken together with everything else the dogs body is saying, as well as the situation as a yawn can be saying different things.
Photo by Steve Jurvetson- CC BY 4 flickr.com
- Askenasay, J.J. and N. Askenasay (1996). Inhibition of muscle sympathetic nerve activity during yawning. Clin. Auton. Res. Aug; 6(4): 237 – 239
- Bully, J. E. (2008). Mind the muzzle: Using Facial Expression as a Correlate of stress Level in Domestic Canines. Journal of Young Investigators. Available at: <http://www.jyi.org/issue/mind-the-muzzle-using-facial-expression-as-a-correlate-of-stress-level-in-domestic-canines/>
- Gallup, A. C. and G. G. Gallup (2007). Yawning as a Brain Cooling Mechanism: Nasal Breathing and Forehead Cooling Diminish the Incidence of Contagious Yawning. Evolutional Psychology, 5(1): 92 – 101
- Provine, R. R., Tate, B. C. and Geldmacher L.L. (1987). Yawning: no effect of 3-5% CO2, 100% O2, and exercise. Behav. Neural. Biology. Nov; 48(3): 382-393
- Romero, T., Konno A. and Hasegawa, T. (2013). Familiarity Bias and Physiological Responses in Contagious Yawning by Dogs Support Link to Empathy. PLoS ONE 8(8):e71365. doi:10.1371/journal.pone.0071365
- Romero, T., M. Ito, Saito, A. and Hasegawa, T. (2014). Social Modulation of Contagious Yawning in Wolves. PLoS ONE 9(8): e105963, doi: 10.1371/journal.pone.0105963