This morning on Lake Harriet in Minneapolis, Hennepin County between 8:00 - 8:30 am both the adult Great Black-backed Gull, and an adult Lesser Black-backed Gull were roosting relatively close to each other on the ice. They were with about 100 Gulls still lingering on the ice and all of them departed at once.
I do not know who has this location in their CBC count.