This gull was photographed in the Coastal Plain near Houston and Galveston, Texas on December 28, 2005; it was one of three LBBG-types seen there that day. It stood out as having a paler mantle than the other two birds, and having a rather blocky head shape, extensive large pale markings internally in the median coverts (and some lessers), and a generally frosty look. It was quite aggressive, challenging Herring Gulls to morsels dropped by smaller gulls.
I was rather surprised by the paleness of the inner primaries from above; also that the outer tail feathers were still growing-in:
Note below the large whitish "thumbprint" on the lower tertials, and the broad pale tips to the upper tertials, lower scaps and even some upper scaps:
The axillaries and underwing coverts are extensively white, with limited brown tipping - this seems too pale for presumed 2nd-generation LBBG underwing coverts?
Below compare the mantle tones of the LAGUs and this bird; in the field I judged it to be either the same tone as the LAGUs or very lightly paler; I've never before seen a LBBG in Texas that was slightly paler than LAGUs, at the same angle:
The eye is placed well-forward in the head, and the bill seems a bit chunky at the tip:
I was struck by how extensively pale are the undersides to the outer primaries:
For comparison here are two presumed 2CY (second winter) LBBGs from the same date and location;