What is this harsh white patch at the right hand side of the bird?

[Jonas_Wagner]

Here is an explanation of the problem you face:

Photographers: stop clipping your highlights

In my 4-years long experience of helping people get decent pictures and get a grasp at image processing, I often ran into the same problem, which triggers a lot of subsequent problems in sometimes sneaky ways… Photographers keep clipping their highlights and expecting magic in software to forgive their mistake. What’s clipping ? Digital sensors (and not just in photography) can only record signals up to a certain intensity: the saturation threshold. Past that threshold, if you keep increasing…

In your case you are well above base ISO already so the easiest solution for the future would be to just lower it a bit while keeping the other variables the same. This shouldn’t result in much more noise but makes the result easier to work with.