This is a very interesting behavioral activity of this species. Possibly to cool its temperature. Had trouble leading my eye from the horizon in this crop. I scrolled the image to view it in a square which I think works better.
I agree with Bob, the upper BG is distracting, and cropping down to the top of the water would simplify the image.
The head and neck look a little soft on my monitor.
Exposure is good. Like the wing display.
I posted a similar pose earlier and Alfred tells me that it is a way they kill parasites. I tried scroll-cropping that top off and I agree with you. Thanks.
Nice behaviour captured. Whatever it is doing this pose is called "sunning". A combination of opening up your aperture (preferably wide-open) and getting down lower (if at all possible here) would have lessesned the distracting impact of the BG. I also find the light a bit harsh and hense the image is somewhat contrasty...you could try a reverse "S-curve" for this.
I think that the F10 was probably overkill, especially at the distance (considering the degree of cropping). The more than necessary DOF included too much of a distracting background, as noted. Detail, again possibly due to the crop, is a bit lacking. What I was mainly going to point out is that this sunning behavior is as you would surmise, done only when the sun is out, and its very hard to get such an image that is not high contrast with dark shadows. Unless you can position yourself precisely head on shadows will always be a problem. I've seen the GBHs and YCNHs that will quickly fold their wings if a cloud blocks the sun momentarily. regards~Bill