Boy are they ugly! Still nice shots, particularly the second and fourth ones. The first one you probably will want to up the shutter speed to capture the wings flapping, rather than have them blurred. Not sure what camera you used, but I find that a shutter speed of at least 1/1000 second will usually stop this type of action. The third one has a bit of a distracting background. I would have placed the duck more to the left, following the rule of thirds, and maybe tried to hide some of the background birds (Canada Geese?) behind the duck. For the fourth one, I would have placed the duck's head a bit more off centre to the right, so it is looking into the negative space on the left side of the frame.
WesternGuy