When we yawn, it seems like the whole world yawns with us. Let one person start to yawn, and pretty soon everyone else is yawning too. Chimps also yawn contagiously, and possibly some other primates as well.
But what does yawning mean to a dog? Because dogs and humans have been associated for so long, is it reasonable to expect that when we yawn, our dogs will yawn along with us? These are the questions that are asked by two recent articles.
In one of the articles (Joly-Mascheroni et al. 2008. Dogs catch human yawns. Biology Letters 4:446-448) the authors had 29 dogs watching a human yawning, and recorded that 21 of the dogs yawned in response. The authors suggest that this represents a rudimentary form of empathy that dogs might feel for humans, causing the dogs to yawn after they see a human yawning.
In the other article (Harr et al. 2009. Do dogs (Canis familiaris) show contagious yawning? Animal Cognition DOI 10.1007/s10071-009-0233-0), the authors showed 15 dogs video clips of either humans yawning or dogs with either yawns or open mouths, and recorded how many dogs yawned under these circumstances. Only one dog yawned in response to the video clips, and this was to human yawns.
So here we have a difference. One article says that dogs yawn in response to human yawns, and the other article says that they don’t. How do we find our way out of this?
One problem is that there are a lot of unknown factors that could influence the interpretation of these results.
For example, can dogs see and understand video clips? My dog Raja seems utterly indifferent to what is happening on the TV screen, even when there are dogs bouncing around in commercials.
And even if they can see what is on the screen, can they interpret what they are seeing? The other day I came across a website that was talking about the work of Samuel Renshaw, a pioneer in human perception research. The website had a picture that Renshaw showed to people, asking them what the picture represented. I could not figure out what was in the picture until I saw the answer, and then it was obvious to me. If you are curious, take a look at the picture at: https://www.enter.net/~torve/critics/Renshaw/notassmart/notassmart1.html and see if you can identify what is there.
Also, when seeing real human faces yawning, are the dogs responding by yawning through empathy, or are they yawning because of discomfort? In a book called On Talking Terms With Dogs: Calming Signals, Turid Rugaas describes a yawn as a calming signal that one dog gives to another (or to a human) signifying that the dog is not a threat, as a way of defusing a potentially stressful or aggressive situation.
When I first got Raja as a rescue dog, I would extend my hand to him to try to get him familiarized with my smell. He would often yawn in response. I understood this to mean that he was stressed and nervous, and I made sure that I did not push my attention onto him. Could the dogs watching yawning humans have responded by yawning because they were feeling stressed in the experimental situation?
What it comes down to is that some of the time, we know surprisingly little about why dogs do what they do.