Much more intriguing though is the number of individuals that, if found on the Pacific or Atlantic, would be readily identified as the expected taxon in that region. Given the opportunity to "overthink" some of these birds, one may look at the same photograph months later and "aptly" assign a different label.
Here's one of these so-called "Lake Michigan Gulls"; 25 November 2015, New Buffalo, Michigan:
I first spotted this bird in flight, and immediately called it a Kumlien's Gull due to the muted an relatively pale wingtip. My first impression, I've learned, is usually the best impression (given neutral lighting and sufficient views of the upperwing).
I feel a similar-aged Thayer's Gull would average darker primary tips - more blackish than the dark slaty-gray seen here. Here's a 3rd cycle type Thayer's from the same region, from this time last year:
|Michigan City, Indiana. 27 November 2014.|
Now for something a bit lighter - a crisp juvenile Herring Gull showing immaculate plumes for late November:
|Herring Gull. 25 November 2015.|
|A few black marks on the outer tail feathers on an otherwise perfect looking adult.|