Age: Gull identification and aging go hand in hand, with the former often dependent on the latter. As we work on identifying a gull, we should be keen to place it in an age group based on plumage patterns. Age and plumage are discussed below.
Identification: The gray-backed birds on the left and right have slender pinkish-yellow bills with defined black rings. The spotted neck markings and finer streaking on the crown, as well darkish eyes safely relegate them to Ring-billed Gull (2nd cycles). Note the 1st generation outer primaries that are holding on (brown), which is expected at this time of year, with new incoming 2nd generation primaries growing in (black with white apical spots). These one-year old Ring-billeds are starting to show yellowish legs, but it is difficult to appreciate this field mark due to both lighting and a slight delay in bare part color maturation.
The individual in the center is a black-backed species. It's relatively compact, but the solid dark brown upperparts, slender vent region behind the legs and parallel-edged dark bill all look great for Lesser Black-backed Gull. By direct comparison to the Ring-billeds, it is a notably small Lesser, likely a fm type. This too is a 2nd cycle, retaining old 1st generation primaries while molting the inner primaries.
It should be noted that these birds are undergoing their 2nd complete molt (known as the 2nd prebasic molt). Therefore, they are now 2nd cycle gulls.