The first thing I see is the bird isn't in focus, the tree branches look a little sharper.
The levels are off and favoring the right by quite a bit. Bring up the blacks and the whole photo will look shaper with better contrast.
You shot at 1/1000 sec which should be fast enough for a 420 mm telephoto. But even the branches aren't as sharp as they could be. How much of a crop is this?
This is what your levels look like.
This is with the levels optimized.
It does appear that the camera focused on the branches and not the bird. But I think it still can be sharper. The other thing to look at is VR. Did you wait for VR to settle down before pressing the shutter?