A dog's tail language is robust and complex and offers a glimpse into their emotional lives. But is wagging it a voluntary action or simply an involuntary reflex which allows them to wear their hearts on their sleeves, or in this case, their tails? Perhaps it might be a little bit of both.
Tail Muscle Control
Your dog's tail may seem to have a mind of its own, but the muscles that control it don't. Just like the rest of her body, she can control her tail muscles by thinking in order to manipulate movement. She can raise, lower or wag her tail at will, and she can stop it mid-motion, too. Some breeds use their tails help with keeping balance, so it's necessary to have voluntary control over its muscles.
Many experts believe that tail wagging is a socially learned behavior as puppies don't wag their tails immediately after they're born. Your dog's tail is kind of like an emotional barometer, and it's important for dogs to convey their emotions to their social group. While we readily associate a wagging tail with a happy dog, the angle and nature of the wag could mean agitation or anger, too. Though different tail wags probably signify different emotions, given their complexity, not all sources agree on the meaning of each type of wag. It's probable that individual dogs have their own unique tail-wagging language.
Stop & Go
Dogs can control their tails and their tail wags, but it appears they often start wagging out of instinct, not conscious thought. It's kind of like a human frowning. You might begin frowning as an ingrained as well as habitual response to, say, an inappropriate joke, but you can return your mouth to resting, smiling or a deeper frown at will. As such, tail wagging appears to be a response to stimuli that can be manipulated by conscious thought. That makes it part involuntary and part voluntary.
If you're confused why your dog's wagging her tail, look at her for other signals. If she looks tense, she may be upset. If she looks relaxed, she may be happy. Tail movements alone are sometimes hard to read. There are no hard and fast rules, but a languid wave is probably a positive wag and a stiff wave is probably a negative one. Dogs lower their tails when they're intimidated or trying to make peace, so a low tail wag probably fits into that arena. You can take note of your particular dog's tail wags to make your own personal dog-tail-wagging dictionary if you want to get a better understanding of your canine friend.
By Nicholas DeMarino
Davidson College: General Physiology of Dogs
WiseGeek.Org: Why Do Dogs Wag Their Tails?
Animal Planet: Why Do Dogs Wag Their Tails?
Marisa Laudau, Northeastern University: Creating a Template of Nonverbal Cues for Immobile Recipients to Use in Communicating with Service Dogs
About the Author
Nicholas DeMarino is a journalist and former newspaper associate editor and reporter. His work has appeared in "The Arizona Republic," "The Billings Gazette," "San Antonio Current" and in other publications. He holds a master's degree in journalism from the University of Oregon.