As one watercolorist to another, those are really good. You're not charging NEARLY enough, though. You could ask at least double what you are for that size. Note to everyone on BYC.....buy one now before he raises his prices!!
I actually do sell my paintings in several galleries, and I do sell them for many times over this amount. But...these are so darn fun to do. I have 16 hens in the backyard, and I love to sketch their myriad gestures. They hold their poses for only an instance, but it's great fun to recall them and get them down on paper. So...it's sort of a labor of love to make paintings from these sketches.