Harsh light as mentioned, always a challenge on a two toned bird like this. I might try to tone down the whites a bit more, many are in the 245-250 range.
Some noise/processing showing up in the shaded white areas on the breat.
Nice pose with excellent head angle.
I might be tempted to trim back the stump by the bill a bit, it is too close. Some might just remove the other stick completely, but a little more space between bill and stick would help.
Beautiful pic, Tim. Quite some noise on the bird, specially in the shades. Have you cropped it in a lot (unlikely since you've had round about 1,200mm FFE reach)? Just wondering whether the 600mm without the TC might have been clearer - perhaps with a CP filter?
I'd try to bring back the blacks a little without darkening the whites using luminosity masks but I'm afraid the noise is going to be your biggest stumbling block here.