Below is another set of photos of "what I imagine a 1st cycle hybrid" might look like. Ethan Gyllenhaal and I observed this individual in Northern Illinois on 23 Dec 2014 - neither of us was comfortable assigning a label to it:
Features that seem intermediate or atypical for one or the other species:
- Straight, thin, black bill more like LBBG than Herring.
- Neat, brown, plumage aspect with checkered wing coverts.
- Inner-primary window is not typical for Herring but too pale for LBBG.
- Thin tail band with white upperwing coverts, and whitish outer tail feathers.
Is this an Appledore Gull? Who knows. Off to the next one...