Docked Tails: The Long and the Short of It

When it comes to canine communication, much of the tale is told by the tail. It is well known that dogs broadcast a lot of information about their emotional state and intentions using their tails. Observing tail signals can tell us whether a particular dog is happy, worried, or threatening. The specific motions that the tail makes—like whether the tail is held high or droops to a lower position—combined with the speed that it moves conveys a lot of information. While all of this may be generally well known, people forget that in order for the tail to be an effective means of communication there has to be enough tail to be visible. Consider for example a note that I received about a Labrador Retriever named Molly. It read in part:

After her accident [involving a collision with a motorcycle] the vet had to amputate her tail, leaving a stump of only around two inches. She recovered okay and still has a personality that is good with people and kids (just like before the accident) but something has changed in her dealings with dogs. We always took her to an off-leash dog park not far from our house and she always had good relations with the other dogs. Since her tail was cut off though, other dogs seem to be suspicious of her and they don’t come up to her the same way they used to. A few have actually snapped or growled at her, which never happened before. Could this be because her tail is gone so that the other dogs can’t understand her tail communications anymore?

The idea that the tail length of a dog might affect its ability to communicate is something that I have been thinking about for a number of years. The reason this has bothered me is because of the practice of tail docking, wherein a dog’s tail is deliberately cut short in certain breeds of dogs, such as Rottweilers, Doberman Pinchers, Cocker Spaniels, Boxers, and so forth. Certainly common sense should tell us that docking significantly limits the usefulness of tail signals and thus reduces the effectiveness of a major channel of communication in dogs. This issue concerned me, but for a long time I could find no data in the scientific literature that addressed the question of whether dogs with short or missing tails had signaling problems.

I decided to try to shed some light on the matter so I carried out a fairly simple observational experiment. In our study we observed dogs interacting in a confined city park area where dogs were allowed to be off leash. We tallied 431 encounters between dogs. Most of these (382 or 88 percent) were typical canine greeting behaviours, often followed by play behaviours including the usual chase games. The remaining 49 encounters contained an aggressive element on the part of one or more of the dogs involved. These could be as mild as a snarl and a snap with no physical contact or, in one case, as severe as an actual physical assault drawing blood. The dogs that we observed were coded simply on the basis of whether they were tailless (most likely docked) or with a tail (undocked or only partially docked). To be classified as being tailless the dog had to have a tail that appeared to be shorter than approximately 6 inches in length (we eliminated small toy dogs from the sample confining our observations to dogs that stood around 18 inches at the shoulder or more). The proportion of dogs with tails was considerably higher in this population, amounting to 76 percent, as opposed to 24 percent of dogs without tails. However, when we looked at the dogs involved in aggressive incidents 26 of these confrontations (53 percent) included dogs without tails. On the basis of the number of dogs with and without tails, we would have expected only 12 aggressive incidents (24 percent) to involve tailless dogs. The surplus number of confrontational incidents involving tailless dogs is highly statistically significant when we do the appropriate calculations: our results show that dogs with short or absent tails are twice as likely to have aggressive encounters as dogs with longer and hence more visible tails. One cannot help but wonder if the increase in aggressive encounters in short tailed dogs might not have to do with the ambiguity or absence of appropriate visible tail signals that could have indicated a social versus a hostile attitude on the part of the docked tail dogs, thus allowing other dogs to steer clear of a potential conflict.

Although I found our results interesting, I worried a bit about the possibility that this study might be flawed. This is because many of the dogs that have docked tails are working dogs designed for guarding and protection functions, such as Rottweilers, Boxers or Doberman Pinchers. Dogs bred for such purposes might be expected to have a somewhat more forceful and insistent personality which might lead them into more confrontations with other dogs. While it would be important to eliminate the differences in the temperament different breeds might bring, we obviously couldn’t go around randomly docking the tales of various breeds of dogs for the purposes of our investigation. So we were left with suggestive but not conclusive results.

Fortunately, science progresses and definitive answers are eventually discovered. In this case a clever pair of biological researchers, Steven Leaver and Tom Reimchen of the University of Victoria in British Columbia, figured out an alternative way to test to see if tail length affected how dogs communicate with each other. Their procedure completely avoided any confounding due to the breeds of dogs involved. They constructed a robot dog which stood around 20 inches at the shoulder and was stuffed with cotton and covered with black synthetic fur so that it looked much like a Labrador Retriever. It could be fitted with a 12-inch long tail or a 3.5-inch short, stubby tail, and these tails’ movements could be remotely controlled.

Starting with the long tailed version of their robot dog, they placed the mechanical canine in an off-leash exercise area. They found that when the robot’s tail was wagging (in a manner which was a nonthreatening signal) other dogs would approach it in what looked like a playful manner; however, when its tail was held upright and was motionless (a dominant threat signal) the other dogs avoided it. This is exactly what we would expect if the dogs were reading the robot’s tail signals as if it were a real dog. Next the researchers replaced the long tail with the short “docked” version and on another day placed the robot dog out in exercise area. Now the other dogs approached it cautiously and in a guarded manner, regardless of whether the tail was wagging or not. The impression the researchers got was that the other dogs were acting as if they could not make up their minds as to whether the robot would receive their approach in a friendly or a hostile manner.

Obviously a real dog with a docked tail could try to use strategies involving other aspects of their body language to offset some of their problems associated with a missing tail. However this study shows that, at the very least, dogs with short docked tails are at a disadvantage when interacting with other canines and this disadvantage can place them in jeopardy of misunderstanding by other dogs. The evidence shows such cases of disrupted communication might lead to aggressive encounters. Tail movements and tail positioning are vital channels of communication among dogs and perhaps we humans should think twice before we dock our dogs tails and deprive them of its benefits—especially if the tail docking is being done solely as a matter of fashion or style.