He's Back. For the severalth consecutive year. This bird usually appears in September in the north and central part of the county before working its way slowly south and hanging out some in New Buffalo and then mostly northern Indiana by the time winter rolls around. This bird is frequently claimed as a Chandeleur Gull (a Kelp x Herring population that survived for a decade or so in the Gulf of Mexico on some little islands that were wiped out in a hurricane). The Louisiana ornithologists who studied the Chandeleur Island birds say it isn't one.
I emailed Al Jaramillo last year about it who thought Great Black-backed x Lesser Black-backed would be more consistent with its appearance, with the obvious caveat that likely it's impossible to prove.
The bird was up close in New Buffalo and that explanation makes a lot of sense.
A close-up of the head. It has the heavy gony angle of GBBG and the brilliant orange spot of LBBG. The gape of both Herring and Kelp is yellow, this bird's is definitely not yellow. GBBG and LBBG have red and red-orange gapes respectively per Sibley.
Another shot of the spreadwing.
Chandeleur birds, there's a good description of the spreadwings of their birds inside.