Sorry to keep dragging this out, but I typed in Thayer's Gull into my search
engine and came up with something pretty cool. Go to the site Herring 
Gull v.s. Thayer's Gull and check out the 1st year birds. They are clearly 
Thayer's and even lighter than the Gull that is at School House Pond. These 
are documented Thayer's Gulls and most of the wing patterns on the tertials, 
secondary and primaries can be matched up feather by feather comparison. 
Put the photo's up side by side. Pretty neat to me. The head shape and bill
are the only differences that I see.
Thanks for putting up with me.
Sean McCandless