Netop, en gammel hun i helt nyanlagt dragt uden mindste spor af igangværende fældning.
Hvis ynglen er mislykkedes, kan fældningen snildt være begyndt tidligt og være færdig allerede nu.

Med så klart gule øjne er der givetvis tale om en temmelig alderstegen dame.

Modsat hvad feks. 'Fugle i Felten' angiver, er undersiden ret varmt farvet. Typisk iøvrigt at gamle hunners længdestriber bliver pilspidsformede (især på flankerne), og er mere eller mindre rustrøde.

Læg også mærke til de store hjerteformede pletter på underhaledækfjerene. Ungfugle er svagere stribet på bugen og har helt ensfarvede lyse underhaledækfjer.

Se også hvor meget den nyligt debaterede hybrids undervinge ligner denne Blå Kærhøgs!

I hate to be a pain in the ass, so please forgive me, but to me this is a young male Hen Harrier, not typically marked on the body, but nevertheless a juvenile male.
The most important difference is in the barring of the primaries and secondaries. Adult females have really strong black bands in the secondaries, with sharp and contrasting edges against an almost whitish background, while the black bands across the primaries are regular, neat and straight bars. In juvenile males the primary barring is typically irregular, often partly missing, and the secondary bands are far less contrasting compared to adult females (bands are not black,the edges are softer and the background is smoky grey, not whitish). Often the median band, like in this bird, is notably narrow, which you don't see in adult females. The body of most adult females is almost whitish, with distinct dark drops or spots, quite similar to a juvenile Goshawk.
As far as I can remember, I have never seen a female Hen with completed moult by mid-September. Please,look up the two adult females on the netfugle gallery from Stigsnaes from early September 2011, and compare. And yes, they are both moulting, and therefore only showing 4 fingers!

Very interesting!

In the field Helge and I tentatively called it a juvenile male (mostly because of the underwing-pattern and the iris-colour), but seeing the images it dawned upon us that it had to be an adult female!

According to available literature (including the brilliant work of reference you did...), the streaking of the underparts is neat and less contrasting to the ground-colour in juveniles.

Never bold and dissolved into irregular spots, blotches and arrow/heart-shaped markings as seen here (note the huge rusty markings on the flanks, so typical of adult females)
The undertail-coverts should look uniformly pale/rusty were it a juvenile, merely with thin, barely visible shaft-streaks, never with prominent, big, bold and heart-shaped spots (again a typical trait of adult females).

I certainly don't want to go out on a limb and argue against your vast experience, but the fact that the underside, from chin to tail, is a text-book example of an adult female in fresh plumage (which explains the richness of colour), is strangely puzzling.

Completed moult by mid-September could perhaps be seen in individuals whose breeding had failed and therefore had started moulting a month or so earlier?

In sum a puzzling bird (as if hybrids weren't enough!) which I am fully prepared to re-label juvenile male. In your opinion the wing-markings are obviously more important than the body-plumage, and I would be very surprised if you weren't right in this matter......but I have yet to see a photo or skin of a juvenile with such body-markings.

If you do find one, please let me know:-)

Best regards
Peter