What are Tails For?
Tails are indispensable for canine activities. Even such mundane functions as balance and motion are facilitated by the often mocked canine appendage. Watch how a dog uses it's tail for balance, like a tight rope walker's pole, when navigating a narrow path. Dogs bred for running have long narrow tails used to aid in making high speed turns. In such cases the front legs are thrown into the turn, but the back legs continue in the original direction. To counteract that, the tail is pointed into the turn.
Beyond physics though, the tail is an extremely important communication tool in several ways.
A wagging tail causes muscles to contract which causes the anal glands located under the tail to release a scent unique to each dog. A dominant dog carries it's tail high and wags to spread the scent, whereas a less dominant dog keeps his tail low, covering the anal glands.
Newborn puppies pretty much spend all their time eating and sleeping and have no need for communication and therefore do not wag their tails. 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. They have learned that they can communicate intentions to litter mates with their tails and avoid conflicts or to possibly instigate one.
The tail's position, specifically the height at which it is held, can be considered a sort of emotional meter. A middle height suggests the dog is relaxed. If the tail is held horizontally, the dog is attentive and alert. As the tail position moves farther up, it is a sign the dog is becoming more threatening.
As the tail position drops lower, it is a sign that the dog is becoming more submissive, is worried, or feels poorly. The extreme expression is the tail tucked under the body, which is a sign of fear.
Other common tail movements:
● A slight wag, with each swing of only small breadth, is usually seen during greetings as a tentative, "Hello there," or a hopeful "I'm here."
● A broad wag is friendly: "I am not challenging or threatening you." This can also mean: "I'm pleased." This is the closest to the popular concept of the happiness wag, especially if the tail seems to drag the hips with it.
● A slow wag with the tail at half-mast is less social than most other tail signals. Generally speaking, slow wags with the tail in neither a particularly dominant (high) nor a submissive (low) position are signs of insecurity.
● Tiny, high-speed movements that give the impression of the tail vibrating are signs the dog is about to do something, usually run or fight. If the tail is held high while vibrating, it is most likely an active threat.
Recent studies have found a right/left bias in tail wagging indicate state of mind. In humans, the left brain is associated with positive feelings, like love, a sense of attachment, a feeling of safety and calm, whereas the right brain is associated with fear and depression and behaviours that require energy such as fleeing or fighting.
Since the left side of the brain controls the right side of the body, it follows that the happy, positive feelings of the left brain would bias the tail wagging to the right (dog's right).
So what happens with dogs who are appendagely challenged? Anecdotally, it was reported a dog which had always formed playful relationships at a local dog park was assessed very differently after an accident which required amputation of her tail.
To study this Dr. Stanley Coren conducted an experiment involving 431 dogs and found that of the encounters involving aggressive elements, the majority involved dogs with docked tails. However there may be a confounding element here in that dogs with docked tails are often more aggressive breeds to begin with. Researchers at the University of Victoria carried this one step further by building a robot Labrador Retriever with a replaceable long and short tail.
They found that when the robot was placed in a dog park with the long tail wagging, other dogs approached in a friendly playful manner, however when its tail was held upright and was motionless (a dominant threat signal) the other dogs avoided it. This is what would be expected if it were a real dog. The tail was then replaced with the short tail and all dogs avoided it whether the tail was wagging or not.
So it looks like dogs depend on their tails for a variety of functions which makes one wonder why evolution left us humans without one.