These images are from April of this year. They are details from larger pictures, and they are not well-focused. They are, however, interesting for what they show, a Ring-billed Gull (Larus delawarensis) perched atop a Red-bellied Turtle (Pseudemys rubriventris) on a log in the Potomac River. (The Red-bellied Turtle is endangered in Massachusetts, but it is fairly common in the Washington area.)
I imagine that the bird had no idea that it was standing on a turtle , and the turtle had no idea that it was being stood upon by a bird.