Dog Tails and Social Signaling: The Long and the Short of It

My dog’s tail is a study in perpetual motion. It wags when he’s happy and when he’s nervous, when he leaves a room and when he enters one, when he stands in a doorway snorting at me in an attempt to communicate his desperate desire for a walk or a toy or a treat. Even late at night, when I’m reading in bed and he’s asleep on the floor beside me, I’ll hear the thwap! thwap! thwap! of his tail, twitching while he slumbers.

Dogs may not have voices, but they have very active tails, and they rely heavily on these furry appendages to communicate. A fast, wagging tail can signal excitement and playfulness, whereas a tail tucked between the legs is a sign of submission. A dog that’s feeling aroused, confident, or aggressive may hold his tail up high, while a relaxed pooch lets his tail hang down lower and looser. These tail movements provide important clues about how a dog is feeling–especially to other canines that may be sharing the same sidewalk or dog park.

That’s another reason, experts have argued, to object to tail docking, a barbaric procedure in which several inches of a puppy’s tail are amputated, often without anesthesia. The pain and suffering that cosmetic tail docking can cause are reason enough to oppose the practice, and they are, indeed, the most commonly mentioned objections. Less often discussed, however, is the possibility that removing  most of a dog’s tail may actually hamper its ability to communicate with the rest of its species.

I recently came across an ingenious little study that illuminates this problem. The study–run by two biologists at Canada’s University of Victoria and published in the journal Behavior in 2008–makes use of my new favorite experimental apparatus: a life-sized robotic dog.

The faux dog–made of synthetic fur, wire, and cotton–resembled a black Lab and had two different detachable tails: one short (9 cm in length) and one long (30 cm). A motor mounted inside the dog’s wire frame allowed the researchers to make both of these tails move using a remote control.

The robo-dog, with the short tail on the right and the long tail on the left.

The scientists set the robotic dog out in “areas of high off-leash domestic dog activity” in Canada, and videotaped nearly 500 different real dogs approaching the impostor under four different conditions: when the robot’s tail was long and still, long and moving, short and still, and short and moving.

The results varied according to the size of the dogs the researchers were observing. Dogs smaller than the robot were cautious in approaching the impostor, regardless of the tail length and movement. Of course, such caution makes sense when dealing with a strange beast that could be twice your size.

It was among the large dogs that the interesting behaviors emerged.  These dogs were most likely to approach the robotic model when the robot had a long, moving tail. (They did so 91.4% of the time.) That makes sense, the researchers say. “Because the long tail was flexible, the simulated motion appeared to us to resemble that of a loose, wagging tail of a real dog,” they write. This kind of loose wag is often an invitation to play–and a social signal that the wagging dog means no harm.

On the other hand, a dog that is holding its tail perfectly still isn’t giving off such obvious “come hither” signals, and large dogs approached the robot with a long, still tail significantly less frequently–only 74.4% of the time.

But when the researchers swapped the long tail for the short one, these preferences disappeared. Large dogs approached a short-tailed robot with a wagging tail just as often as one with a motionless tail (85.2% and 82.2% of the time, respectively). These findings suggest that the dogs were less able to discriminate between a tail that’s wagging playfully and one that’s standing still and erect when the tail itself is short. “It appears that the signals communicated by differences in tail motion were most effectively conveyed when the tail was long,” the scientists write.

The large dogs were also twice as likely to pause while approaching the short-tailed models, perhaps using that time to try to decipher whether they should continue moving closer. As the researchers put it in their paper, “As the efficacy of a visual signal is related to its visibility … it may be that larger dogs had a harder time interpreting the ‘intentions’ of the model when the tail was short.”

Taken together, the findings suggest that docking a dog’s tail may impair its ability to communicate effectively with its canine comrades. And it’s yet another reason–if there weren’t enough already–to put a stop to the cosmetic amputation of dog tails.

ResearchBlogging.org Reference: Leaver & Reimchen. (2008). Behavioural responses of Canis familiaris to different tail lengths of a remotely-controlled life-size dog replica Behaviour, 145 (3), 377-390 DOI: 10.1163/156853908783402894

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9 Responses to Dog Tails and Social Signaling: The Long and the Short of It

  1. Janis says:

    I’ve heard that that was the whole point behind tail and ear docking for fighting breeds — to prevent them from signaling “uncle” to one another so that they would continue to fight, even to the death. It short-circuited their typical means of communication. That was when I realized that yes, tail-docking is bad, and particularly bad in conjunction with trimming off the ear flaps.

  2. Natasha says:

    I haven’t ever heard such a thing. Given the breeds I can think of with docked tails are not fighting dogs by original breed (Pembroke Welsh Corgis, Rottweilers), I can’t imagine that’s the only reason to dock tails.

    Which isn’t to say docking is a good thing. I know a person or two who insists it’s important (in Rottweilers, the breed I grew up with), but they usually just sound silly to me, to be honest.

    As for the post, I remember once, growing up, my mother telling me that every Rottie person she knew agreed that Rotties got along better with fellow Rotties than

  3. Natasha says:

    My apologies. I don’t know how my reply posted when I hit the space bar. I must have fumbled on my keyboard.

    Anyway, mother told me that every Rottie person she knew agreed that Rotties got along better with fellow Rotties than other breeds. I asked why and she said, “Well, I figure it’s because they’re tails are docked and so they talk funny. I bet it’s easier to get along with someone who talks funny the same way you do than someone who doesn’t.”

    That comment has stayed with me for years, partially because it made so much sense. And it has certainly helped me conclude that docking is not a thing my mom’s old friends ought to be up in arms about, even though I know they are. An intact tail is great.

  4. Luisa says:

    @Janis: a myth. A pit bull signals “uncle” during a fight by “curring out” — quitting, turning away, trying to escape from the other dog. Thumb through any book on pit bull terriers [I've got at least a dozen, some written by dog fighters and some by show ring aficionados] and the fighting dogs with natural ears will vastly outnumber the dogs with cropped ears. Tails: not docked. Cropped ears are more of a fashion statement than anything else. At AKC and UKC dog shows, cropped ears for Americn Pit Bull Terriers are the norm, unfortunately.

    People involved in dog rescue occasionally see some horrible DIY crop jobs.

    Tail-docking is more common among gun dogs — English Spaniels, Cocker Spaniels, Weimaraners, German Shorthaired Pointers — due to the belief that a natural tail is more easily injured when the dog is working in the field. That’s what the proponents of tail-docking say, anyhow.

    I’d be inclined to support a ban on both procedures, and certainly on ear-cropping.

  5. Terry says:

    I have a black lab. Her tail is her rudder in the water. It’s beautiful to watch her
    use it to steer quickly from one direction to another. I can’t imagine a lab
    without a long tail. Her tail is her method of communication. Her tail makes
    her whole body shake when she greets me. It is truly one of the happiest
    things of my life.

  6. ange says:

    Corgis, though, have short tails due to a genetic defect, not normally due to docking.

  7. Natasha says:

    Really? I did not know that! I assumed it was a dock.

    I do know a “natural bob” can happen. I knew a Rottie breeder who was thrilled to get a natural bob female when I was a kid, but I never realized it was extremely widespread in other breeds. Thanks for the education. :D

  8. Pingback: Why bobbing your dog’s tail is really bad idea

  9. RRCD says:

    I have always questioned the reasoning behind the use of a robot to explain communications skills of a living animal, and don’t feel it should be taken as serious scientific evidence in supports of anti-docking.
    Why would research being gathered on animals not be done with use of a variety of breeds? The fact that animals are colour blind and rely on their other senses like scent and hearing to determine the difference between a non-living and living being would give the animal early indication that the robot was no threat to them . And if you add a moving object to the robot it would only make that dog more curious and want to approach it.
    To me using a robot for research on a dog for communications is like introducing a human to a mannequin for the first time.
    Here are many reasons –if there weren’t enough already–to allow Veterinarians the right to continue these much needed procedures Docking, Cropping and Dew Claw removal in purebred dogs.
    http://rrcd.ca/my_tail_and_I.html