Dogs are able to communicate many different emotions and response by the height, placement, curvature, and movement of their tail. For example:
Tail horizontal, straight out and stiff – ‘I'm boss’ – can be seen when dogs are trying to established who's boss. This dog is looking for trouble and can be an early warning sign of a possible dog fight.
Wide tail wag that is so strong it pulls the hips from side to side and nearly sends the dog off course – can be exhibited in greeting especially after a long absence. It may be reserved for the dog’s favourite person or pack leader.
Tail up and slightly curved up over the back – ‘I’m the the boss and everybody knows it’ – this dog knows it is so confident and that they are boss and nobody will question it.
Some dogs however have short tails, either due to docking or a few breeds are born with short tails such as Boston Terriers, Pembroke Welsh Corgis or English Bulldogs. When a dog’s tail is not visible or is considerably shorter, it means they are unable to communicate the right signal to other dogs, which can be misinterpreted by other dogs and lead to an unwanted response from other dogs.
A number of docked tails are nearly not visible because the tail is completely out of sight, but some have a bit of length to them and appear to be in a constant upright and stiff position. This can then be interpreted by some other dogs as confrontational because a stiff, upright tail suggests the dog is trying to establish ‘who’s boss’ and often means the dog is looking for trouble, even though the dog in question is simply unable to change the shape and height of their tail, which can lead to an attack when it is seen by other dominant dogs.
A study by Leaver and Reimchen in 2008 placed a life-sized model of a dog (similar to a Labrador Retriever) in a room with a wired-tail that could be remotely controlled, and could display four different appearances; short/still, short/wagging, long/still and long/wagging. They then observed the interaction of 492 off-leash dogs in a dog park to see whether they freely approached the model or hesitated first. The researchers found that the dogs were more likely to approach the long/wagging tail than the long/still tail. They also took longer to approach the short/still and short/wagging tails, but did not differentiate between the two and approached the model at the same rate. The results highlighted that a longer tail is more effective at conveying different cues to other dogs, and highlights that a shorter tail impairs communication between dogs, as they are more hesitant to approach a dog with a shorter tail.
Dogs with docked tails are therefore at a disadvantage when socializing with other dogs, and it can put them in a difficult position if they mean perfectly well, but other dogs misread their signals leading to an altercation. Rightfully so, tail docking is now illegal/restricted in over 70 countries including the U.K, the Netherlands, Germany and Ireland. Tail docking is still unrestricted in many countries including the U.S.A and France. Find the full list here.