It’s something we all know: our dogs wag their tails because they’re happy. Because they’re thrilled to see us. Because they love us. But it turns out that what we “know” may not be the truth. Or it may be only part of the truth.
As certified behaviorist Pat Miller wrote in her article “Tell-Tail Signs: What’s Your Dog’s Tail Language?”, just because a dog’s tail is wagging doesn’t necessarily mean it’s happy. It simply means the dog is stimulated. It certainly may be happiness or excitement that’s the stimulation, but it could also be anxiousness, fear, or even aggression. (Yes, contrary to popular opinion, an angry dog approaching you could also be wagging its tail. Just ask someone who’s been bitten by a tail-wagging dog.) You need to carefully observe the dog’s entire body to reach any kind of meaningful conclusion about what that wagging tail really means.
Think of it in human terms: while we may use our hands to gesture, those gestures can have a variety of meanings, depending on the context. We might be pointing toward something, we might be explaining how tall or short or long something is, we might be gesturing while telling a story, we might be using our hands to communicate our excitement or love or even dislike. Yet even though these kinds of gestures are linked to communication, other gestures can be instinctive and spontaneous, not something we do intentionally. The same could be said for dog tail-wagging.
How Did Tail-Wagging Evolve?
Four European researchers recently investigated over 100 past studies on dog tail-wagging to see if any patterns emerged that would give a single, conclusive answer as to how dog tail-wagging evolved, as well as what it means. That research led them to develop two main theories about the evolution of tail-wagging: first, that over the tens of thousands of years that humans worked to domesticate dogs, breeding them for traits like friendliness and tameness, we unintentionally selected for tail-wagging because it was linked to those positive characteristics.
The second theory that emerged was that we bred dogs for tail-wagging because of an innate yet unconscious human appreciation for rhythm. “Perhaps because humans have this sort of propensity for rhythmic themes, we were actually breeding dogs that wagged more,” explains Taylor Hersh, one of the study’s authors. “We may not have been aware that we were doing it.”
The Many Meanings Behind Tail-Wagging
So, why do dogs wag their tails? No one doubts that dogs wag their tails to communicate, but beyond that, opinions range far and wide.
For instance, some research suggests that the directionality of a tail-wag can express a dog’s emotional state: a tail that wags more to the right may suggest the dog is curious and wants to approach, while wagging to the left can mean the dog is uncertain or wants to retreat.
The position of a dog’s tail can hint to its general mood and feelings as well, say other researchers. For instance, according to veterinarian Dr. Brittany Grenus, graduate of Tufts Cummings School of Veterinary Medicine, when a dog is showing happiness or friendliness, their tail will be either parallel to the ground or held slightly upward or downward and wagging in sweeping side-to-side movements. “The more excited a dog is, the faster their tail typically wags,” she says, and in times of extreme excitement, you’ll often see what can only be described as a whole-body wag.
On the contrary, a tail held low, pinned down against or tucked between a dog’s back legs, strongly indicates insecurity and submission. Sometimes, that low position can be accompanied by a fast wagging motion that’s only at the tip, which tends to show that the dog is anxious, fearful, or perhaps wants to appease another dog.
Do Other Animals Wag Their Tails?
Dogs aren’t the only mammals that wag their tails, but they are by far the species that does it the most. While dogs wag primarily to communicate, other animals “wag” their tails for different reasons: whales swing their tails in order to move through the water; horses, cows, as well as many wild animals like moose, elephants, zebras, and giraffes use their tails to swat away flies and other pests; flying squirrels glide from tree to tree by moving their flat tails like rudders; white-tailed deer often wag their tails in alarm or when they’re about to run from a threat.
You might think that because dogs are descended from wolves, wolves might also be tail-waggers, but generally, the answer is no. While wolves frequently use their tails to communicate, they score almost at the bottom of the persistent-tail-wagging scale when compared to their evolutionary heirs. While subordinate wolves will wag their tails during reunions after separation, Taylor Hersh explains that “What we don’t see in wolves is this huge amount of tail wagging across a variety of situations. In wolves, it’s mostly confined to a submissive individual signaling to or appeasing a dominant individual. They’ll wag their tails slowly and often pretty low.” What you’ll never see in wolves is the I’m-so-happy-I-could-burst kind of tail-wagging we see in our domestic dogs.
Some people also believe that foxes and coyotes wag their tails, but again, researchers have never been able to confirm this. In fact, in Portland, Oregon, where coyotes are pervasive, the Portland Urban Coyote Project states that “You’ll never see a coyote’s tail held high or wagging. If you see that, you are probably looking at a dog.”
Foxes will hold their tail high in signaling to other foxes, and fox cubs will shake their tails rapidly while begging their parent for food, but there’s no evidence that foxes actually “wag” their tails.
The Future of Tail-Wagging Research
While we know a fair amount about why dogs wag their tails, further research could have a number of advantages. For instance, learning more about tail-wagging behavior could have profound animal welfare impacts. A case in point is the practice of tail-docking, which many researchers and animal ethicists say not only causes unnecessary pain, it also may have an adverse impact on a dog’s ability to communicate with other dogs. At the same time, it negatively affects a dog’s balance and support.
Additional research into why dogs wag their tails would certainly allow us to understand more about dog behavior and their interactions with both humans and other dogs and will help close the gaps in the scientific literature as well. The experts who explored the studies on dog tail-wagging are hoping for a more in-depth examination of the phenomenon, including neuroimaging through noninvasive brain scans. One of the questions they’d like to answer is whether our dogs’ tail-wagging is conscious or unconscious. Perhaps, as with human gestures, they’ll discover it’s a little bit of both.
In the end, while science—and our own experiences as dog lovers!—can offer some clues and ideas, a great many mysteries remain about why dogs wag their tails..
