South Sweden early April (1 Viewer)

[Macswede]

There were 3 birds that I was unsure of during our trip to Skåne in the far south of Sweden from 4th-9th April.
There was also 1 other bird that I was able to identify quite easily but that I think may be of interest. I also a little uncertain of the correct terminology.
1. Some kind of duck. Female Wigeon perhaps?
2., Wood or Green Sandpiper (or something else)
3. More ducks, a pair this time. Gadwall?
4. My heart raced when I saw this beautiful white gull but I quickly realized that it was another white Black-headed Gull. There was a large flock.
I want to call it a leucistic Black-headed Gull but I remember reading somewhere that the term is overused and it is much rarer than most people think.
I think it its appropriate here and I've certainly never seen another gull like this one but I'm curious to know for sure.

 

[Alexander Stöhr]

Hello,
1. first is a male Mallard in an iD-unfriendly posture
2. Green Sandpiper, most Wood SP have brighter legs, a more distinct supercilum and heavy barring to lower breast sides and upper flanks
3. Common Pochard, everything is there, please note good colours for this species
4. leucistic Black headed Gull, right shape and the right head pattern is still visible, this would be different, including bill shape (stouter, drooping) in most similar Med Gull

 

[Macswede]

Thank you very much Alexander! Green Sandpiper is what I wrote in the trip list so I don't have to change that but I'm mentally kicking myself for not recognizing Mallard and Pochard (not on our list).
I'll go ahead and post a picture of the leucistic Black-headed gull in the gallery.