Icterine warbler, Hippolais icterina, Härmsångare
Thanks go to Peder Winding, birdwatcher, who swiftly identified the bird.
A fairly big warbler with a large head, broad based bill and long wings with a quite short square ended tail. The upperparts are greyish-green and the underparts are uniformly light yellow. It has pale lores and a rather vague yellowish supercilium with a pale eye ring. Other distinguishing features include a panel on the folded wings formed by pale edges to the secondary feathers and tertiary feathers and the grey, sometimes bluish legs. English Wikipedia (Creative Commons Attribution-ShareAlike License))
I first thought it was a juvenile yellow wagtail, since I was shooting one before and after this one. See photo stream. But this one has more yellow and the beak seems orange or yellowish. Overall, it looks more like some kind of warbler, the more I look at it (which makes more sense sitting in a tree and all). On one shot, the mouth it really wide open, and it looks like a juvenile bird begging for food,