I'm not too sure to be honest.
Usually when I'm shooting into the sky I will over-expose in order to bring some detail to the subject, otherwise you just end up with a dark subject with unrecoverable detail.
I've 'worked' on the Buzzard to bring out the highlights, though there was good sunlight on the underside of the bird.
I'm not technically minded when it comes to photography, so apologies for the poor answer to your question.
This is a low-res, uncropped version of the original...
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