I do not consider myself a gull expert. I find them quite difficult to identify. On our return from Prescott, Wisconsin, Erika and I stopped at the Number Two Lock along the Mississippi River in Hastings, Minnesota. This photo was taken during a blizzard, so it is not optimal. The black line through the eye, the very dusky sides of the head and neck, the broad, white window at the wings, the relatively dark back, and the very pink legs all are field marks of the Slaty-backed Gull. Note the yellow eye. The red spot on the bill also seems to be the shape seen on some Slaty-backed Gulls. Compare the dark back to that of a nearby Herring Gull (second photo).