Why do dogs wag their tails?

Tails serve many practical purposes for our canine companions, from giving them better balance while running to spreading their unique scent to other dogs nearby. Tails are also one of our pets’ key ways of communicating, letting others know when they’re feeling nervous, excited or open to communication. By watching your dog’s wag, then, you can better understand how he’s feeling and what he’s trying to say.
 
Dogs use their tails, face and body posture to communicate, making his tail one of your pet’s primary means of expressing his moods. In fact, studies have shown that dogs only wag their tails when they’re with company, making it a completely social activity. Watching a dog’s tail, how it’s positioned, whether it’s relaxed and how fast it’s moving can communicate crucial information. A tail held high usually signals enthusiasm, for example, and confident canines tend to hold their tails higher, allowing them to spread more of their scent. A dog holding his tail extremely high or wagging only the tip, however, is likely on high alert and you should avoid him or proceed with caution. Those with their tails low or between their legs are more timid or feeling nervous. Similar to tail height, the speed of a dog’s wag can tell you a lot about his mood. A loose, relaxed wag generally means a pet is in good spirits. The “full body wag”—when a dog’s whole body is relaxed and sways with his tail’s sweeping motions—usually means a dog is ready for a friendly interaction. A tense, stiff wag indicates tension or hostility. Watch for the rate of a dog’s wag, too, as brisk tail wagging is generally a good signal, while slower motions can indicate your pet is feeling apprehensive or unfriendly.
 
Perhaps the most common misconception about dogs is that a wagging tail means a happy pet. While dogs certainly wag their tails when they’re happy, the gesture simply means an animal is paying attention and open to communication— not that he’s in a good spirits. Because it can be difficult to gauge a dog’s attitude just from his tail, watch the rest of his body to better understand how Fido is feeling. It’s worth noting that tail movements and their meanings vary from dog to dog and across breeds, making it important to get to know your pet and his unique body language. Dogs with docked tails have difficultly communicating with their canine peers, so you leave your dog’s tail unaltered so he can fully participate in social life.