Why dogs wag their tails

Most dog owners know that like humans, dogs feel a range of emotions. Joy, fear, anger, sadness, anxiety, love, anticipation, surprise, jealousy, and loneliness are among those emotions that our best buds experience. But without the ability to develop a vocabulary, they need another way to communicate. So why do dogs wag their tails?

“Dogs ‘talk’ with their tails. The position of the tail can tell us a lot about how a dog is feeling; hung low suggests fear and submission, whereas held high is a sign of dominance and arousal”, says Charlotte Corney, zookeeper and founder of The Wildheart Trust.

A wagging tail often conveys happiness and excitement, but neuroscientists at the University of Trento in Italy have found that the speed and direction of wag is also important.

The team found that when dogs are looking at something they want to approach, such as their owner, they wag their tails to the right. But when confronted with something they’d rather back away from, such as another dog displaying an aggressive posture, they wag their tail to the left.

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Of the positive responses (wagging their tail to the right), perhaps unsurprisingly, they also found that dogs wag their tails faster when greeted by their owner. They also found a medium, positive response was exhibited in dogs met by an unknown human, and a very low (but positive) response when greeted by a cat.

Understanding these behavioural asymmetries in tail wagging, could be beneficial to understanding your pooches positive or negative emotions, as brought on by different stimuli. In other words, it’s a non-invasive method to tell us what your dog likes and dislikes.

But it’s not just tail wagging that helps dogs convey emotion. According to a literature review carried out by veterinary researchers at the University of Bari, dogs have a behavioural repertoire when communicating with humans and other dogs. They have a vast range of visual, tactile, acoustic, and olfactory signals, that they use for expressive and fine-tuned communication. In lowering their tails, for example, they are attempting to reduce the appearance of their size and avoid conflicts with other dogs.

Your dog is saying something different depending on the direction they are wagging their tail. © Getty

Although they can exercise a certain amount of control, tail wagging in dogs is largely seen as an instinctive response to stimuli. You might remember a certain dachshund that made the news at the start of the pandemic, Rolo. He was so excited that his family were working from home during social distancing, that he sprained his tail from too much wagging. Thankfully, Rolo has since made a full recovery.

“Like all essential doggy business, such as breathing, barking and begging for treats, tail wagging uses energy. When a dog is happy, knows it, and really wants to show it, muscle cells in the tail produce the energy that is needed via a process called aerobic respiration,” explains Dr Helen Pilcher.

“This uses oxygen, but if the tail wags too much, and the muscles work really hard, the cells start to respire anaerobically, without oxygen. This generates less energy, and a by-product called lactic acid which causes temporary muscle fatigue and soreness. It’s enough to make even the most exuberant pooch take five and wait for its cellular batteries to recharge,” says Pilcher.

Dogs who wag their tail in their sleep are probably dreaming. © Getty

Just like us, dogs go through sleep cycles of Rapid Eye Movement (REM) sleep and non-REM sleep. And it’s during REM sleep where they likely have the most vivid dreams. Yes, dogs dream – and if you’re wondering, what do dogs dream about, they’re probably dreaming about you.

Your pup’s nighttime adventures are likely made up of fragments from their real life. So, all that real-life tail wagging from car rides, walkies, dinner time, trips to the beach, and most importantly – when you come home from work, are likely being relived in doggie dreamland, resulting in happy, excited, or content tail wagging.

Sometimes dogs will wag their tails in their sleep for other reasons. If they’re experiencing anxiety, potentially from a nightmare, are cold or feeling submissive, this may result in a different type of tail wag. It’s often obvious when dogs are wagging their tail in their sleep for more unsatisfactory reasons, as it will usually be accompanied by other noticeable signs, such as shivering if cold, or whining if having a nightmare.

Dr Pilcher is a science writer specialising in biology, medicine and quirky off-the-wall science. She's written many popular science books, and her latest book, Life Changing, How Humans are Altering Life on Earth (£10.99, Bloomsbury Publishing PLC) was shortlisted for the Wainwright Prize for Writing on Global Conservation, and is out now.

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The tail wag: a cute way our dogs tell us they’re happy…or is it?

Although looking at the way a dog is moving their tail can help you to understand how they are feeling, it’s really important to also take note of what the rest of their body is doing, along with their facial expression, to get a better picture of their body language.

Puppies aren’t born wagging their tails, as cute as that would be! Tail wagging develops differently in different breeds, but it usually begins around three to four weeks into life.

The wag of a tail is instinctive in dogs; it’s used as part of their varied communication with one another and with humans.

While tail wagging is instinctive, the shape, size and way the tail moves will vary from breed to breed and individually. For example, most golden retrievers have large expressive tails that tend to swish from side to side when walking, whereas whippets and greyhounds tend to hold their tails far lower than the average breed. The spitz breeds, like huskies and malamutes, have tails that curl backwards; sometimes the tip of the tail will even touch the dog’s back.

Despite these differences, along with the size and shape of today’s breeds, most dogs tend to understand each other and communicate well if they are socialised appropriately.

If you have a puppy, it’s a good idea to introduce them to a range of well-behaved adult dogs of differing breeds – this way they will get used to the variations within their own species and not become fearful of unfamiliar breeds or dogs of different sizes.

Dogs missing part or all of their tails may have an immediate disadvantage over other dogs in terms of their communication skills. Tail docking makes it harder for owners to read their beloved pup correctly, and more difficult for other dogs to understand them too, especially if the tail has been docked close to the body.

A dog with a docked tail loses one of their most valued communication methods. This means that their intentions to other dogs might be miscommunicated and an owner or person interacting with the dog might not fully understand how the dog is feeling.

Many people believe that a waggy tail means you have a happy dog, but it’s important to take into consideration what is happening around them at the time and, more importantly, what the rest of your dog’s body is telling you about their current mood.

Tail expression:

A broad, smooth, sweeping tail (not tucked or high) means the dog is currently relaxed and comfortable
Helicopter tail (the type that moves in circular motions) is normally reserved for people your dog knows and for their close doggy friends. This usually indicates he or she is feeling excited and particularly social. If you’re getting the helicopter tail, your dog is really pleased to see you!
If your dog’s tail wags slightly to the right, research suggests this could indicate your dog knows the person or dog and it is a wag of recognition
A tucked tail, or a tail that is a lot lower but wagging slightly, usually means the dog is worried. Usually used to communicate “I’m no threat” to other dogs and people.
A tail clamped between your dog’s legs means that your dog is really worried and they feel the need to protect themselves
A high tail that’s wagging fast often indicates arousal and excitement, but how the dog really feels will be down to all sorts of factors, such as breed, their individual personality, what the rest of their body is doing and what activity they are doing at the time
Some dogs tend to move their tails from side to side rapidly when focussing on a scent. You might see this is in your own dog if they are searching for a toy you have hidden or have picked up an interesting and exciting smell to track. This movement doesn’t serve to communicate to others; it’s thought just to be a sign of extreme concentration (much like when we humans push our tongues out when concentrating hard!).

You should always be aware of signs that your dog or puppy is feeling worried. These could include:

avoidance, moving away, hiding
tail tucked under, looking away, appearing ‘smaller’
lip licking, yawning (when not sleepy), paw raising
growling, flashing teeth, snapping, biting

If your dog displays any of the above behaviours you should stop what you’re doing with your dog and give them some space.

It’s important to remember that our dogs use their whole body, including the tail, to express how they are feeling, and it’s our responsibility to do our best to pay attention to, and understand what they are ‘saying’.

Always be alert and sensitive to your dog’s communication to keep them happy and safe.