Why Do Dogs Wag Their Tails?


You’re at a friend’s house and along comes her collie, Baby, wagging her tail. Good girl! You bend over to pat her and are rewarded with a growl. What went wrong?

“It is so important for people to realize that a wagging tail does not equal a dog that is friendly or wants to be petted,” says E’Lise Christensen Bell, veterinarian and board certified veterinary behaviorist at Veterinary Behavior Consultations of NYC. “It can, but you are much better off looking at the entire dog.  If there are stiffened muscles, dilated pupils, tense facial muscles, or ears pinned forward or back, these are signs that you should back off.”

Dogs use their tails to communicate strong emotions such as agitation, annoyance and anger as well as happiness. A person can get bitten by a dog that’s wagging his tail because he read the signs incorrectly. And make no mistake; there is a science to tail wagging.

Dogs have been wagging their tails since…well, there have been dogs. These furry masses of bones serve multiple purposes. The original purpose of the dog’s tail was for balance. It prevents him from toppling over as he makes sharp turns while running or swimming. The tail also balances him when walking along narrow structures, climbing or leaping. Over time, the tail adapted itself to playing a vital role in communication, particularly when a dog is just walking or standing around.

Puppies don’t come right out of their mom’s womb wagging their tails. The majority of them don’t begin wagging until they are about a month and a half old when they have a need to communicate with their litter mates or mothers.

For example, if there’s too much “rough-housing” between the pups, one of them might wave their tail like a white flag to signal a truce to its littermates. As they grow, they wag their tail to beg for food from the adults in their canine family.

Next, we’ll look at what the various tail positions mean.

“It is a misconception that a tail wag is a sign that the dog is happy,” says Beth Strickler, DVM of Veterinary Behavior Solutions. “This is one of the reasons that children are often unable to differentiate between a friendly dog and a non-friendly or aggressive dog.”

For help with figuring out what the tail wag means, look for the direction of the wag or at how fast his tail is moving. Studies show that dogs wag their tails to the right when they are happy and to the left when they are frightened.

If Baby wags her tail high and back and forth, she’s in her “happy place”. When she’s just being plain nosy, she will keep her tail horizontal to the ground. When Baby’s tail is tucked between her hind legs, she’s either frightened or being submissive. When she’s wagging it low, she’s worried or feeling insecure about something.

Dogs wag their tails for other dogs, humans, and other animals like cats. But research shows that dogs don’t wag their tails when they are alone because there is no need. Just as humans use smiles and body language as social cues in different situations, our canine friends do the same.

“Dogs are much better at reading each other’s body language than we are,” says Dr. Bell. “Dogs that are behaving appropriately in social systems use their bodies and tails to communicate with other dogs even as they are observing the tails and body position of other dogs. This helps them avoid unnecessary conflicts.”

Dogs also wag their tails to spread their natural scent from their anal glands. Each dog has a scent that’s unique to him or her. An “alpha” or dominant dog that carries his tail high will release more of his scent than a dog that carries his tail lower. Often, when we see a dog holding his tail between his legs, he’s frightened and doesn’t want to release his scent. This is his way of flying under the radar.

Since tails are essential to communication, pooches without tails typically approach other dogs with caution so there’s no miscommunication or fights between the two animals. A playful pup might not be able to interpret cues from the tail-less dog, so he doesn’t back down, causing the tail-less pooch to resort to biting or other acts of aggression if he feels threatened.

Since dogs haven’t yet figured out a way to talk to their owners and their other animal cohorts, they have to use their bodies to communicate. The eyes, ears and body positions are a few clear indicators of how they feel. But wagging their tails is one of the most visible and well-known ways canines use to clue people and other animals in on exactly what’s going on with them.

A dog’s tail is a very important feature of her body. The original purpose of this furry mass of bones was for balance while walking on narrow surfaces. Dogs also use their tails to help them make turns while running or to guide them while swimming. But for generations of pups, tail-wagging has additionally been an effective tool to let their owners and other animals know if they are happy, sad, anxious, scared or even feeling aggressive. So, is tail-wagging involuntary, or voluntary?

“We can’t talk to dogs so we don’t know if they think about the tail wag and then do it, or if it just occurs due to the neurochemical effects of a certain state of mind,” says Lisa Radosta D.V.M. and owner of Florida Veterinary Behavior Service. “However, you can watch dogs in a dog park and know that the dogs have an intent when they hold their tail a certain way or wag it a certain way.”

The America Society for the Prevention of Cruelty to Animals (ASPCA) expert Dr. Stephen Zawistowski believes it can vary. On the ASPCA Web site, he advises to “think of tail wagging like a smile. Sometimes you smile without knowing, and sometimes you can make yourself smile. I think dogs are the same with their tails. Sometimes it just happens, and other times it seems like they ‘think’ about it.”

A 2007 study on dog body language that appeared in the journal Current Biology found that the different sides of the dog’s brain dictate the direction of the tail wag. A dog will wag his tail to the right side of his derrière when he is feeling happy, positive or confident about approaching something. The left brain, which controls the right side of his body, specializes in behaviors that scientists refer to as “approach” and “energy enrichment.”

On the other hand, the dog will wag his tail to the left of his derrière if he feels scared or wants to bolt from the situation. The right side of a dog’s brain controls feelings of withdrawal and energy expenditure and also controls the left side of his body.

So, wagging is both innate and learned, says Dr. Radosta. If a dog learns that a certain body signal, such as tucking her tail, keeps her safe from a threat, she is likely to use that signal again. She reminds us of the story of Pavlov’s dog, a classic example of conditioning. When Pavlov rang the bell, the dog salivated. He didn’t have to think about salivating, he just did it. It was an innate behavior which was under the control of a stimulus (a bell).

Dr. Radosta says the changes in tail wag and tail carriage depend on the stimulus and can occur very quickly. As a result, experts believe that the tail is also under voluntary control. You don’t need to go any further than your dog’s veterinarian’s office to prove this fact.

“Any veterinary technician who has tried to take a dog’s temperature rectally will tell you that the tail can be tucked quickly to avoid a rectal thermometer,” says Dr. Radosta.