Age: The adult-like gray scapulars down the middle of the back and lightly marked uppertail coverts immediately suggest a 2nd cycle type. Also, the solid black tertials with relatively wide white edges support a bird not in its 1st plumage cycle.
Identification: The largely uniform brown wings and dark gray central scapulars point to a dark-backed species. The checkered lesser and median coverts are suggestive of Lesser Black-backed Gull. The lightly barred/marbled region in the tail feathers (specifically the partition between the black tail band and white uppertail coverts) also resembles LBBG, and that's what this month's quiz bird was identified as.
Berrien County, Michigan. September.
Here's a more detailed photo of this rather "large" Lesser:
