Jon, I agree with Rakesh on the crop and would even take a bit of the top. You could even crop just after the second branch in the middle and focus in even further (with equal part of the top).
I like it Jon. As a stand alone photo it's a bit ambiguous, but it makes me imagine it as a background to text, or a greetings card. I guess on the whole I like its atmosphere more than I like it as a picture of a whitethroat.
I like your idea for a "birdscape" of sorts but I think for it to work really well, I think you needed a different situation with the bird totally unobscured, angled a bit more parallel to the camera, more evenly lit, and tack sharp.
The large OOF vegetation on the right also detracts. Would be better if all of the vegetation were closer to being on the same plane and more equally sharp.
These are tough images to pull off but can really be great when it all comes together.