Hans got a sms of Anton Liebermann who is at this moment on Christiansø together with Mikkel Lausten and Peter Lyngs. They believe it could be a Buskrørsanger/Blyth's Reed Warbler. Going through the information I have this is a real possibility. The second primary is much shorter that the third and fourth primary (unfortunately I only have an unsharp picture of that, but it shows it clearly). The head pattern is certainly pointing to Blyth's reed warbler and not to the Paddyfield reed warbler (supercilium stops at the eye), which is another species with a short second primary. The notch on the second primary is 14,5 mm and the wing length is 65.

This is a species that has to go to the commission and lets hope they will accept the bird for Denmark.