Hi John, I like the composition, pose, and background on this shot. As is, I feel the tree trunk dominates the shot. You didn't mention what the crop was, but if you have it, I would try cropping in more to showcase the nuthatch. Thanks for sharing this!
John a fine shot, I wonder if you have used any filters, the detail is very strong in the bark of the tree, and fungi (?) I would be tempted to make it less significant. I appreciate you may well have chosen this becasue it is an interesting perch but I feel it is too dominant.
If the image could take it I would crop a little tighter (I am guessing you considered the portrait version and found the trunk too big?)