It seems f/4 is rather wide for getting most of the bird in focus. It did a nice job on the perch though.
Flash helped you with sharpness at a lower s/s than recommended for your focal length.
This reminds me of my late friend AlexC, God bless his soul, who would say "I know what the bird looks like so I don't need to see it" :) I think it works here, just wish you had a little more light in the tail. Very nice background, btw.
Looks like you were put in a tough situation! Opening up to get the fastest shutter speed works against sometimes, and I feel that this is the case in this image. Your subject looks excellent, and you've got him against a very complimentary background. The shallow DOF makes areas of the image a little more noticeable and distracting (the areas of moss/lichens to the left of your little hummer). My eye also keeps getting drawn to the tip of his beak. Keep up the good work ;)
I like the composition....nice diagonal branch with bird in third of frame. The little branch on main branch might be distracting, but kind of mimics the bird so I don't really mind it.
Have to agree with better DOF, however.