By Dr. Becker
New research suggests dogs send messages to each other through tail wags.
According to a study published in a recent issue of Current Biology,1 the direction of a wag is quite significant. What looks like just another friendly wag to you or me is actually communicating important information to other dogs.
As it turns out, when dogs are feeling stressed they tend to wag their tails to the left. The reason for this, according to the study’s lead author, Giorgio Vallortigara of the University of Trento in Italy, is that tail wagging is a reflection of what’s going on in a dog’s brain. Activation of the left-brain causes the tail to wag to the right, and activation of the right-brain produces a wag to the left.
Tail Wags to the Right Signal Openness, Wags to the Left Signal Wariness
In an earlier study, Vallortigara and his team demonstrated that dogs wag to the right side when they encounter something pleasant (like their owners). When they see something threatening, for example, a strange dog exhibiting dominant behaviors, they wag more to the left side. Those study results raised the question of whether dogs notice another dog’s tail wagging and use the information to decide whether the dog with the wagging tail is friend or foe.
For the most recent study, Vallortigara and his team used videos of a dog or dog silhouette wagging its tail mostly to one side or the other, or not wagging at all. The only thing moving in the wagging videos was the tail.
The video was shown to 43 dogs, including mixed breeds, Rottweilers, Beagles, Boxers, Border Collies, and German Shepherds, who were equipped with heart rate monitors. When the video dog wagged primarily to its left, indicating a negative response, the dogs in the study tended to have faster heartbeats than when the video dog wagged to the right or not at all. The dogs’ response also suggested a higher degree of stress.
Left-brain activity in dogs resulting in tail wagging to the right means they are having a positive response that invites another dog to approach. Right-brain activation suggests a negative withdrawal response.
Study Concludes Dogs Read the Tail Wags of Other Dogs
The study concluded that dogs who see another dog wagging to the left experience anxiety and elevated heart rates, whereas dogs who see another dog wagging to the right remain relaxed.
The researchers don’t believe the dogs are intentionally sending signals with their tails, but rather the tail wagging is a consequence of the inner workings of the canine brain. Tail-wagging behavior results from the way in which different emotional signals activate different parts of a dog’s brain.
"These results suggest that dogs have perceptual and attentional asymmetries," says Vallortigara. "So for example, if you are going to visit a dog, if you are vet, there will be probably a side which is better with respect to the probability to evoke a more friendship response or to evoke a more aggressive response."