Elsa is a confident girl, but a very smart one. She was very young here, 6 mos. old maybe. So her tail was probably a little higher than it would be today if she met this dog. It quickly lowered as he delivered his message that he was not sharing his ball. She ran off after their first meeting but was very intrigued by this grouchy male.
"Oh look how happy she is." I heard this I don't know how many times when Tilley was out in the middle of a field. Happy? Yes but she was not wagging out of happiness, she was excited by a trigger. Shadows were a trigger for Tilley and when she saw one her tail would immediately go up and wag like crazy. A wagging tail means just that; excitement. You have to look beyond the tail to read more into what a dog is feeling. Often a wagging tail is a bad thing.
Elsa has a full tail and because of this it is much more active. Many times it is just the very tip that is wagging so for dogs with amputated tails you won't see any movement, only positioning of the tail. Tails are so very important, they should be left on dogs and not amputated for our viewing pleasure. Often when Elsa is in the office with me for a long period of time; I will hear the thump of her tail. I know what it means, she is bored and getting goofy. If I look at her at this moment she will show her teeth to me and turn upside down hoping I'll join her on the floor; sometimes I do, sometimes I don't.
So Elsa and Tilley's tails wagged in these situations but neither meant that they were happy. An extremely aggressive dogs tail will wag as well, highly held with a stiff wag is not a good thing. There are many ways to wag ones tail and it a nice window into a the dog's mind. BUT; it is essentially important to watch the tail and the rest of the body. Below is a great article on tail wagging.
Tail wagging article
Watch your dog's tail, it will give you a great deal of information. Elsa had a low slung tail for two days; this is highly unusual for her and let me know that she was most definitely not happy or feeling well after she was spayed. Now at a full week after her spaying it is back up to full mast. Just yesterday she did the tail thumping in my office, it made me smile to know that she was getting back to her old self.
Watching tails and understanding a dog's body language is very important. Many people think they know but they don't. I have often approached people with my dog who is wagging. I know my dogs and for Jessie it was bad news; tail held high wagging stiffly. Had the other person approaching understood body language they would have also seen her ears up, direct stare, hair up on her back and a very stiff little body. But all they saw was that cute little face until they got too close; even with my warnings.
No a wagging tail does not mean happy, the tail is just a piece of the whole puzzle.