Hi Johan-
The blue BG sets off the yellows and browns of the bird nicely. Nice catchlight in the eye--really helps to have with that dark head. Composition is fine by my tastes. Might want to consider removing the horizontal branch as to me it is a little distracting. Alex
Johan- You had harsh light here and not much you could do, although a better sun angle would have been from behind rather than to the left. I like the simple perch but I would crop from below to lose the small branch. A better head angle would have the bird looking a little towards you rather than away.
Not in my experience Johan. I never use them for bird photography because of the cost in light. A polarising filter in this situation cuts down on sheen (which you really don't have here), but then just reduces the amount of light across the board, so dynamic range stays the same.