Looks like you did fine on the exposure...maybe brighten it up just a tad.
The head angle is fine. You did fine with the catch light in the eye.
The bird does look soft. I'd sharpen that a little more...just the bird.
From an 'art' perspective, the background isn't to desirable due to all the
branches, with the major distraction being the branches "growing" from
the Flicker's head.
You could probably lessen the distraction by performing a vertical crop
on the Flicker. I would start the crop on the right side of the Flicker where
the first branch is going up. Then crop on the left and either the first or second
vertical branch. After that you could probably do some cloning by getting rid
of some of the left over branches, which would clean up the background a lot.
Over all a nice shot. I am not too concerned about the branches 'growing out of it's head'. To me in that regard, it is clearly a bird among the branches.
Based on the body and lens combination I would be slightly disappointed at the sharpness. It is a little soft, the camera seems to have just missed tack sharp focus. Not too difficult to add a touch more sharpness. The level of cropping may also be playing a part, I have no idea how far you were from the bird.
Under the same shooting conditions I would have been at ISO 640 f/6.3-8.0 and the corresponding higher shutter. Less chance of tiny amounts of camera shake, and away from wide open.
Thanks for the feedback so far. I wasn't pleased with the sharpness either and I will work on that. The distance was approx. 40 yards, so I had to crop it big time.
A nice opportunity but the bird is soft. That body and lens can give excellent sharpness, and even wide open at 400mm it should be very good. There are many issues that can degrade sharpness. If it isn't excellent to start with, a big crop can reveal softness, and noise reduction will cause softening. It's hard to tell from a JPEG but it looks like missed focus may be a contributing issue here, too. The center point has invisible helper points and if it is a big crop it's possible it hit one of the branches. And the camera can focus slightly differently with subsequent shots that should be identical otherwise. I try to shoot several, with a re-focus each time, in hopes one will be better.
Your shutter speed should be good if your hand holding technique is good. Palm under the lens on the zoom ring, not touching the focus ring, elbows tight against your sides, camera pressed against your forehead, and a steady stance.
I prefer to use "silent shutter" mode unless I need the fastest burst speed for action, in the hope that it might give a little less mirror shake. I have never seen it claimed that it would matter at our normal shutter speeds, and haven't tested it, but no harm in trying everything I can.