Age: This individual shows several plumage characters that are obvious, sub-adult, traits. The tailband, brown marginal coverts and "dirty" black primary coverts, combined with a heavily marked bill, all suggest a bird that isn't an adult (despite the largely white body). The plumage looks typical of a 3rd cycle type. Note that the broad white edges on the flight feathers (specifically the tips to the secondaries and inner primaries) are not expected on a 2nd cycle.
Identification: Few gulls in North America show a menacing pale eye such as this with pale gray upperparts, and pink legs. The bill is not dramatically large or bulbous-tipped. This species is one that anyone who has a veritable interest in gulls should know - the archetypical seagull, if you will. The January quiz bird is an American Herring Gull. Although many 3rd cycle Herrings show a p10 mirror by now, this one does not.
Here's an open wing of this individual:
|THIRD CYCLE TYPE HERRING GULL. CHICAGO. FEBRUARY.|