Age: Our quiz bird in the center of the frame appears to be an adult black-backed species, but the extensive black on the bill is excessive for an adult. An open wing may reveal subadult features on the plumage. The smaller white apicals are also atypical of adults. Such birds are best referred to as "adult type", which implies some ambiguity in age.
Identification: Adult black-backed species can be sorted into two groups: those with yellow legs and those with pink legs. This individual appears to have intermediate leg color -- not the obvious pink seen on the two Herrings in the foreground, but also not the mustard-yellow seen on the Ring-billeds in the background. The legs do, however, have a dull yellow cast to them, which is not uncommon in adult type Lesser Black-backed Gulls. The bill pattern too is found on a good number of adult type Lessers. The size and structure seem to fit that species, and the clear iris and finer head streaking also support Lesser. It's upright posture and lowered wings give the body a rotund shape, almost recalling Slaty-backed Gull, and from a distance, such a wide tertial crescent may excite observers. But the attenuated look to the wings, leg color and extensive black on the bill all combine to make our August Quiz a relatively straightforward Lesser Black-backed Gull.