Within the Great Lakes areas, Thayer's Gulls are a special treat to witness, and are only seen during the cold months of the year. They arrive in late fall, stick around for the winter, and leave just as the coldest months of spring are approaching; to head back up north to the coasts of the arctic tundra to breed.

The description below is for comparing the two birds in this photo, and is only mentioning what to look for with the adult birds. Both Thayer's Gulls and Herring Gulls reach their adult plumage during their 4th year.

Adult Thayer's Gulls have dark eyes, whereas adult Herring Gulls have pale eyes. Thayer's Gulls tend to have a more round-profile with their form (more compact & rounded head, and more elegant body profile overall). Throughout their wing tips (the black feathers sticking off of their backsides as shown), Thayer's Gulls have larger white spots per feather than the smaller-spotted Herring Gull. Although the books don't mention this, I have found that adult Thayer's Gulls seem to have a "richer" or brighter yellow coloration to their bill, than most adult Herring Gulls have. Gull identification requires looking at very fine subtleties, and I think that the Thayer's Gull is one of the prettiest birds around.