I agree that the bird is sharp, and the head angle OK, but a slight turn towards the camera would be even better - but you can't control what the bird is doing! The bird to me looks as if there is a lot of digital noise, and there's something a bit weird about the contrast - looks like the bird might have been under-exposed and you lightened it in pp, or there was a heavy crop, or both. There are some subtle but noticeable jpeg artefacts in the sky.
Either this is a huge crop or there is something else going on - IQ is quite bad with noise present also.
Looking forward to seeing the original - so we can help.
Paolo mentioned in his data that the crop is down to 2.5 megapixels - that would certainly account for the lack of details and the huge amount of noise. You really can't cut more than 50% an still retain the sharpness and detail, Paolo. Why don't you post the original uncropped and let us see if there might be a less severe/better crop possible.
Hi - The original is way under exposed - Here you should have been using your exposure compensation to add light to this - I would be thinking in the region of +2 and then check your over exposure warnings and histogram.
Here you need to expose for the subject - not the BG - Doing the above would have resulted in a high key image (Sky totally blown out) but the bird properly exposed.
Under exposing introduces noise when adjusted in PP.
The other issue of course is the crop - Just way to big of a crop - IQ will not stand up to that big of a crop.
If you need any help understanding how to use your exposure compensation (If using AV Mode) or to get a correct exposure using manual - you are in the right place, Just ask I am sure plenty will be only to glad to help.
I shot usually in manual mode and when I shot birds in the sky I am always overexposed, between +1 and +2;in this particular situation ,which was against light +3 was necessary.
I agree for the crop; I should stay around 4 MP to have good results.