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Why dogs wag their tails

Original Publication Date: June 1, 2015
By C. Sue Furman, Ph.D.

A dog's tail originally served to balance him while walking, leaping, and making sharp turns when running.

Through time, a wagging tail became a tool of communication. It could express happiness, but not all tail wags send the same message. A swishing tail could declare excitement, fear, insecurity, or stress.

It is now accepted among scientists that the brain is in charge of whether a dog wags his tail to the right or the left. A dog wagging his tail to the right of his rear feels generally positive about something. If he has negative feelings, his tail tends to wag to the left side of his body. However, can an approaching dog interpret the tail swishing dog's intentions?

Giorgio Vallortigara of the University of Trento in Italy studied 43 dogs each fitted with a harness to monitor their heart rate when faced with another dog displaying either a right or left wagging tail. He concluded that the onlooker could interpret the wagger's intention by the direction he swished his tail. An approaching dog wagging his tail to the right did not increase the observer's heart rate, and a relaxed demeanor was maintained. When confronted with a dog wagging his tail to the left side of his derriere, the onlooker's heart rate increased, and he showed signs of stress and anxiety.

Speed of the wag also influences the language of the tail. A vigorous wag to the right indicates the dog is happy to see the approaching person or dog. A slow wag to the left signals the arrival of someone unfamiliar.

The position of the tail is another component of tail language. A dog displays confidence when he stands erect looks straight ahead, and holds his tail high when encountering a new dog. He is signaling a friendly greeting but is also telling the new comer that he is boss.

Why dogs wag their tails Why dogs wag their tails
(click image to enlarge)

If a dog stands tall with his tail wagging back and forth, he is trying to impress you. A dog with totally relaxed limbs and tail is completely unconcerned about the situation. A threatened dog will jut his tail straight out. A tail tucked down and between the hind legs is a classic sign of fear.

When reading the meaning of the position of a dog's tail, be sure to consider the average position that dog would normally hold his tail. The tail language of dogs is subject to dialects similar to a Southerner's drawl. That is because different breeds naturally carry their tails at different heights. Greyhounds and Irish wolfhounds have low slung tails while the tails of beagles and many terriers are carried in an almost vertical position.

Dogs still use their tails for balance, but the lopsided swishes of their tails convey many messages to other dogs and to you if you are listening.

Sue Furman, Ph.D, has published two books and a DVD on canine massage and teaches classes in pet massage, acupressure, first aid and CPR. See her schedule and submit questions at