Wagging tail can mean happiness or warning
November 2011 / Centre Daily Times / State College, PA
The Centers for Disease Control and Prevention estimate that 4.5 million Americans are bitten by dogs each year. Whether their own dog has bitten someone or they have been victims of a bite themselves, many clients have recounted to me their surprise and dismay when the bite occurred, exclaiming, "But the dog's tail was wagging when he bit!"
Many people mistakenly believe that a wagging tail is necessarily a happy tail, and this misconception can lead to trouble. Dogs wag their tails for a variety of reasons, not all of which are designed to convey friendliness. In fact, one type of tail wag, known as the "flag tail", is likely the most misleading wag of all, and one that is commonly seen before a bite. In this type of tail wag, the dog's tail is whipped up high and over his back. It is often stiff and wagging at a fast rate in short arcs. The flag tail wag may be associated with piloerection (that is, the dog's hair may be standing up along his back or tail) or other more obvious signs of aggression such as barking and growling. At other times, however, there may be no other signs of aggression while the flag tail is being displayed.
The flag tail is commonly seen when a dog is charging toward or along his property line while people or dogs pass by on the street or sidewalk. Dogs are somewhat territorial creatures by nature, and the flag tail's rapid wagging pace likely evolved as a means to communicate the dog's threatening presence ("Here I am, let there be no mistake about it!") while the tail's position high over the back communicates increased size ("Look how tall I am, perhaps you should move along quickly!") A passerby paying attention only to the wagging tail may unwittingly reach out to pet such a dog, thinking he is merely saying hello. From the dog's perspective then, his tail wag has not sufficiently threatened the passerby, and he may feel compelled to move to his next defensive tactic, which could include a bite.
Of course, there are some breeds whose tails hang naturally in a curving arc over their backs. A Chow Chow, for example, has a tail permanently arcing over his back, so his friendliest of tail wags could look like the flag tail when it is communicating nothing threatening at all. Clearly, other aspects of a dog's behavior must be taken into account before a formal diagnosis of aggression can be made.
In many other situations, a wagging tail is indeed a happy tail, which is why the misconception arose in the first place. The friendliest of all canine tail wags is what's known as the "helicopter tail." In this wag, the tail moves loosely in all directions in random patterns around the back (high, low, and side to side), and often the whole back end is wiggling with it (the ever-adorable "wiggle butt" we all know in our own dogs). This is the tail wag you are likely to see when your dog greets you after a long day at work. It is also the tail wag we frequently see among puppies. Being an inherently social species known for their unique ability to bond to humans as well as to fellow dogs, this tail wag has evolved as a gesture of friendly greeting and affiliation ("I see you, I like you, I am no threat to you, let's say hi!") Among a dog's many other assets, it is this tail wag that has brought dogs into our hearts and hearths for thousands of years!