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Hi Didier,

I'd agree with Tawny Eagle on both pics but I'm also confused about the barring on the tail of the first bird. I can't think that I've ever seen this on Tawny Eagle, it is rather something you'd expect on Lesser Spotted Eagle. Having said that, the wing shape and tail length don't fit Lesser Spotted Eagle - not to mention the fact that Lesser Spotted Eagle would be happily breeding in Eastern Europe at the end of July. So, of course, would Steppe Eagle so that one is also not really a contender.

You don't have some more pics of the bird perhaps? I'm reasonably sure that it must be a Tawny Eagle. At that time of year and with those S-shaped trailing edges to the wings, I really can't think of anything else it could be but it would be interesting to get some other angles on the bird.

[cautious whisper]I'm not sure if I should consider dark morph Booted Eagle. The barring on the tail and the rounded wings would fit but the blatant lack of "landing lights" and lack of white base to the tail is a problem. Also, when I first opened the picture, I didn't get the Booted Eagle feeling at all, which is probably a strong indicator as they really are rather unique looking birds with which I typically don't struggle. Also, Booted Eagle in KNP at the end of July would be well out of range.[/cautious whisper]

Whens it the correct time to use Juvenile, and immature??!

The terms are absolutely not interchangable. Each refers to a specifically definible moulted set of body plumages.

A bird with its first set of "non-downy" body feathers is referred as being in juvenile plumage.

The next change of body plumage after another full moult, but which is not its adult plumage, is the immature plumage.

If the bird has another body plumage moult, but is still not in adult plumage, it is in it's subadult plumage.

Not all bird have all the stages. Short lived species like passerines can go from juvenile to adult. Longer lived species tended to add the extra stages.
The situation gets complicated in very long lived species (like albatrosses and raptors) where there may be multiple stages of any of the above.

The length of time between body moults also vary depending on the life span of the species. In short lived species there can be 6 months between each moult, a year or more for longer lived species.

The best SA example of a species that has all four plumages is the Kelp Gull which reaches adult maturity at 4 years. I did a population study a few years ago and could age all of the birds in my study group with relative accuracy.

I hope this helps.