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Dog Tails - Why Dogs Wag Their Tails


(Excerpt from How to Speak Dog) Dr. Stanley Coren

“….In some ways, tail-wagging serves the same functions as our human smile, polite greeting, or nod of recognition. Smiles are social signals, and human beings seem to reserve most of their smiles for social situations, where somebody is around to see them. Sometimes, vicarious social situations, as when watching television or occasionally when thinking about somebody special, can trigger a smile. For dogs, the tail wag seems to have the same properties. A dog will wag its tail for a person or another dog. It may wag its tail for a cat, horse, mouse, or perhaps even a butterfly. But when the dog is by itself, it will not wag its tail to any lifeless thing. If you put a bowl of food down, the dog will wag its tail to express its gratitude to you. In contrast, when the dog walks into a room and finds its bowl full, it will approach and eat the food just as happily, but with no tail-wagging other than perhaps a slight excitement tremor. This is one indication that tail-wagging is meant as communication or language. In the same way that we don’t talk to walls, dogs don’t wag their tails to things that are not apparently alive and socially responsive.

A dog’s tail speaks volumes about his mental state, his social position, and his intentions. How the tail came to be a communication device is an interesting story.

The dog’s tail was originally designed to assist the dog in its balance. When a dog is running and has to turn quickly, it throws the front part of its body in the direction it wants to go. Its back then bends, but its forward velocity is such that the hindquarters will tend to continue in the original direction. Left unchecked, this movement might result in the dog’s rear swinging widely, which could greatly slow its rate of movement or even cause the dog to topple over as it tries to make a high-speed turn. The dog’s tail helps to prevent this. Throwing the tail in the same direction that the body is turning serves as a sort of counterweight, which reduces the tendency to spin off course. Dogs will also use their tails when walking along narrow surfaces. By deliberately swinging the tail to one side or the other in the direction opposite to any tilt in the body, the dog helps maintain its balance, much the same way a circus tightrope walker uses a balance bar. Quite obviously, then, the tail has important uses associated with specific movements. However, the tail is not particularly important on flat surfaces, when a dog is simply standing around or walking at normal speeds. At these times, it becomes available for other uses. Evolution again seized an opportunity and now adapted the tail for communication purposes.

It is something of a surprise to many people to learn that puppies don’t wag their tails when they are very young. The youngest puppy I ever saw systematically wagging its tail was eighteen days old, and both the breeder and I agreed that this was quite unusual. Although there are some differences among the various breeds, the scientific data suggests that, on average, by thirty days of age, about half of all puppies are tail wagging, and the behavior is usually fully established by around forty nine days of age.

Why does it take so long for the puppy to start wagging its tail? The answer comes from the fact that puppies begin wagging their tails when it is necessary for purposes of social communication. Until they are about three weeks of age, puppies mostly eat and sleep. They are not interacting significantly with their littermates other than curling up together to keep warm as they sleep or crowding together to nurse. They are physically capable of wagging their tails at this time, but they don’t.

By the age of six or seven weeks (when we start to see tail-wagging behaviors on a regular basis), the puppies are socially interacting with one another. Most of the social interactions in puppies consist of what psychologists call “play behaviors.” It is through playing that puppies learn about their own abilities, how they can interact with their environment, and most important, how to get along with other individuals. A puppy learns that if it bites a littermate, it is apt to be bitten back, and perhaps the game it was playing might be terminated by its now angry playmate. It is at this point that the puppy also starts to learn dog language. It is not clear to what degree these emerging social communications are prewired, but learning is clearly needed to refine the use and interpretation of these signals. The pups learn to connect their own signals and the signals provided by their mother and their siblings with the behaviors that come next. They also begin to learn that they can use signals to indicate their intentions and to circumvent any conflicts. This is where and when the tail-wagging behavior begins.

One place where conflicts are likely to occur is during feeding. When a puppy wants to suckle its mother, it must come very close to its littermates as it crowds in to find her teats. Remember that this puppy is now coming close to the very same individuals that might have been nipping, jostling, or chasing him a few minutes earlier. To indicate that this is a peaceful situation, and to calm any fearful or aggressive response by the other puppies when they too are pushing toward the mother’s teat, the puppy begins to wag its tail. Tail-wagging in the puppy then serves as a truce flag to its littermates. Later on, puppies will begin to wag their tails when they are begging food from the adult animals in their pack or family. The puppies come close, to lick the face of the adult, and they signal their peaceful intentions by tail-wagging. It thus becomes clear that the reason that very young puppies don’t wag their tails is that they don’t yet need to send appeasement signals to other dogs. When communication between dogs is needed, they rapidly learn the appropriate tail signals.

Tail language actually has three different channels of information: position, shape, and movement. Movement is a very important aspect of the signal, since dog’s eyes are much more sensitive to movement than they are to details or colors. This makes a waving or wagging tail very visible to other dogs.

Evolution has used a few additional tricks to make the tails even more visible. Wild canines, like wolves, often have great bushy tails, which are easily seen at a distance. In addition, many tails are specially colored to facilitate recognition of tail signals. Often, the underside of the tail is lighter, to make the high-tailed signals quite visibly different from signals involving the tucking of tails into a lower position. Many canines will also have distinctive markings to make the tail tip more visible. Usually, there is a lightening toward the tail tip, or perhaps simply a white mark which defines the tip of the tail. In other canines, the tail tip is noticeably darker. Either of these two color contrasts helps to make the end of the tail more visible, and this make movement and position cues easier to recognize….”

Excerpted from "How to Speak Dog"
� Stanley Coren All rights reserved
Reprinted by permission
Dr. Stanley Coren is a professor of Psychology.
He has written 11 books on dogs. He was the host
of the television show Good Dog! and currently can be seen on the
television show Pet Central on the Pet Network.
His informational blog is at www.psychologytoday.com/blog/canine-corner
and his website is www.StanleyCoren.com

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