Chicago currently has a few rare visitors: Harlequin Ducks. They usually don't come to this area. There was one around last year, though, so maybe he recommended our fair city to his duck friends.
They were displaying some interesting activity. One of the three would start splashing. Then the other two would splash and all three would dive.
More photos of the Harlequin Ducks are at my bird-watching blog, here.