The tail of the dog!

Or should that be the tell of a dog!

In the funny way that items flow around the internet, I recently read an item that appeared on the daily email summary from EarthSky. It was entitled: Read the message your dog sends with his tail. That, in turn, had been prompted by an article published on the website ScienceDirect. It was a study announced in Current Biology and published on the 18 November 2013, (Pages 2279–2282). Here’s how that article opens (and go here to read the numbered references):

Seeing Left- or Right-Asymmetric Tail Wagging Produces Different Emotional Responses in Dogs
Marcello Siniscalchi, Rita Lusito, Giorgio Vallortigara, Angelo Quaranta


Left-right asymmetries in behavior associated with asymmetries in the brain are widespread in the animal kingdom [1], and the hypothesis has been put forward that they may be linked to animals’ social behavior [2 and 3]. Dogs show asymmetric tail-wagging responses to different emotive stimuli —the outcome of different activation of left and right brain structures controlling tail movements to the right and left side of the body. A crucial question, however, is whether or not dogs detect this asymmetry. Here we report that dogs looking at moving video images of conspecifics exhibiting prevalent left- or right-asymmetric tail wagging showed higher cardiac activity and higher scores of anxious behavior when observing left- rather than right-biased tail wagging. The finding that dogs are sensitive to the asymmetric tail expressions of other dogs supports the hypothesis of a link between brain asymmetry and social behavior and may prove useful to canine animal welfare theory and practice.

Graphical Abstract

Wagging tails

In terms of understanding for the non-scientific minded, then the EarthSky article is an easier read.

Read the message your dog sends with his tail

Tail-wagging is a reflection of what’s happening in your dog’s brain. Learn to read your dog’s tail signals, and you’ll know if he’s happy … or stressed.

Tail-wagging in dogs is the classic signal for happiness. But researchers have found that tail-wagging can mean that your dog is either happy or stressed.

Activation of the left-brain causes a dog’s tail to wag to the right. Activation of the right-brain causes a wag to the left. That’s not new knowledge. Scientists detected that difference seven years ago.

What is new is that, not surprisingly, other dogs can easily read the message your dog is sending with his tail. And so can you.

Researchers at the University of Trento in Italy tested 43 dogs of various breeds for their ability to distinguish between tail wags. They showed the dogs videos of other dogs wagging their tails (much like the one above) and monitored the dogs’ heart rates and reactions. How could they be sure that the dogs weren’t watching their canine buddies’ facial or body cues? The researchers also showed the dogs only a silhouetted version of a tail-wagging dog.

As it turned out, every dog responded the same way. Dogs watching other dogs wag their tails to the left looked anxious, and their heart rates increased. In other words, they, too, became stressed. But dogs watching others swing their tails to the right stayed calm and relaxed — an indication that right wags are an expression of companionship and confidence, according to these scientists.

Why study tail wags in dogs? The team said in the summary to their study, which was published in Current Biology last year:

The finding that dogs are sensitive to the asymmetric tail expressions of other dogs supports the hypothesis of a link between brain asymmetry and social behavior and may prove useful to canine animal welfare theory and practice.

Bottom line: A dog wagging his tail to the right is happy, but a dog wagging to the left is stressed, say researchers.

Let me finish off today’s post with the following video.

So here’s to dozens of people watching their dogs’ tails!

8 thoughts on “The tail of the dog!

  1. That is fascinating research Paul; many thanks. Still, perhaps you would agree, the anxious tail wag is somehow different in its motion; it seems to me that it’s more pulsing and less of a free-flowing swish. At least, that’s certainly how it was with my Border Collie.


    1. Despite there being nine dogs in the house and therefore plenty of opportunity to see the differences, I’m still unclear. However, this research has prompted Jean and me to actively observe wagging differences. Intuitively, I think what you noticed is correct.


  2. This beats which way the dog goes to the Loo… LOL..
    Wishing you a wonderful weekend, and I am sure given your tribe you will have lots of time to see if this theory is right or left.. 🙂
    Enjoy your day..


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