I cant help a lot, but I have seen this bird/a bird very like in Denmark 2 years ago. It did remind very much about dunlin X pec.sand - I dont even know if this exsist but it was the most satisfying explenation I could come up with. (I joked about it was a cox sandpiper - but that isnt dunlin x pec. sand as far as i remember) I have seen pictures of hybrid shorebirds, but not this combination. But I am very happy to see pictures of "my" bird.

Interesting bird. Another possibility is a hybrid between dunlin and white-rumped sandpiper. There has been two reports of such suspected hybrids in Maryland, USA and Ontario, Canada this month. This bird resembles these two hybrids in many respects. Long, decurved black bill and body size similar to dunlin but with streaked upper breast contrasting against a white belly. Did the bird have any arrow-shaped streaks along the flanks? See here for comparison photos of the MD hybrid:
http://www.flickr.com/photos/mikeycerw/4636998575/
and ON hybrid:
http://peregrineprints.com/Blog/Temp/PBurke.htm

My bird had no markings on flanks, the plumage was very much pec. sand. It had adiffereant colleration tone than dunlin more grey/yellowish and nor warm redisb brown like dunlin. Since I wrote last i see that cox sandpiper might be a good candidate they should be very dunlin like.

Hi Frode,

There was no sign of any streaking on the flanks, the bird lacked a white rump and was also too large/robust to be this hybrid. Cox's Sandpiper is also considered in the Netherlands, but it would be rather noteworthy: as far as I know this "species" has only been recorded in Japan and Australia, and furthermore has never been photographed in summer plummage. But bearing in mind the westward expansion of Pec Sandpiper, why shouldn't it be possible that hybrids with this species involved might also appear in the WP...