Age: Both gulls appear to be typical adults with no traces of sub-adult plumes or bill patterns.
Identification: The only thing better than an open wing shot is two open wings for comparison. The gray upperparts are virtually equal in color, and so they're of little help. Suffice to say the gray is pale and any dark-backed species is immediately excluded.
Most useful are the wingtips. To the discerning eye, the bird in front has more extensive black pigment on the wingtip while the other shows limited black and more white. Not only this, the shade of black is slightly paler on the farther individual. The bird in front shows a fairly standard Herring Gull wingtip for the central and western part of the continent, and its pale eye and fairly strong bill agree with Herring as well. The farther individual shows a rather classic Iceland Gull wingtip with thayeri pattern on the 9th primary. The all-white tip to p10 and notable white tongue tips on p6-p8 also point to Iceland Gull. Also note the dusky eye and smudgy head markings, and hints of a smaller bill.
Our October Quiz birds - Adult Herring & Thayer's Gull - were photographed in Superior, Wisconsin in late November.