Thank you all for the helpful comments. I'll go back to this one, and try a vertical comp, with a bit more contrast and some selective USM. I've had far too many birds with soft heads, so I finally did a fine-tuning of the AF with this lens/body combo, and found (as more than one of you has suggested in the past) that I've been forward-focusing. Hopefully I'll post some sharper images in the future (maybe one today). I just wish I could go back and re-shoot all the soft ones.
Bill, agree with what the others have said. You've placed the subject very well in the frame. The head softness could be a combination of insufficient DOF and some motion blur. But clearly your hands were tied due to the low light.
Beautiful image that I studied for several minutes. I've used a positive exposure bias under similar light and consider the result here having me wonder how the black control might benefit. Although the composition is very pleasing, I think a square crop should be considered before a vertical one while losing part of the right side of the frame. You may not have utilized your camera's ISO setting high enough. Always challenging decisions at the moment of the shot.