I found this bird on the morning of December 04, 1998 at Arlington Landfill, Tarrant County (east of Fort Worth), Texas. It was in a large gathering of c.1,500+ Ring-bills and c.800+ Franklin's Gulls (they are running very late this year), and my initial thoughts on seeing it were "Black-headed Gull" - especially as a nearby site hosted two BHGUs late last Winter. But the more I looked (and photographed), the more "odd" it looked, and when I finally saw details of the wing pattern I felt sure it was a hybrid - possibly FRGU x BOGU; perhaps even the bird from Waco in 1991/92. However, when I got my photos back and studied them, I found myself wondering (without any conviction) if there is a possibility that this bird is an exreme example of BHGU? Here is my summary of the pertinent points:

General: size and general structure similar to FRGU; gray of upperparts paler than FRGU - much closer to but not quite as pale as RBGU - such that a broad white tertial crescent is apparent.
Bare parts: legs blood-red, lighter and more red-toned than nearby FRGUs; bill similar red color but with black tip that merged gradually into the red base - slight paleness at extreme tip of maxilla; shapeof gonydal area too deep and "angled" for BHGU?
Head: general pattern of head markings good for BHGU, but blackish perhaps too extensive and slightly odd on auriculars for normal BHGU; blackish patch imm. ahead of eye too prominent, and white eye-crescents a bit too big for BHGU? ; tone of black on head looked same as nearby FRGU. Nape white.
Wings: only P10 - P6 with black subterminally, and P5 with a tiny black "comma" on inner web only (BHGU obviously black on P5 and often P4). From above on P7, P6, there is a small whitish tongue (smallest on P6) on outer web (inside from the black subterminal mark), but most of the basal part of outer web is gray (on BHGU white in outer web - when present on these feathers - runs almost to coverts). Black outer edge to P10 plus small black streak mid-way along white outer web of P9; white tips to P10 - P6 very large - too large for BHGU? Underpattern of outer primaries very odd; pale with short black edges to inner webs of P10 - P6 ( BUT look at photo 23, page 199 of Grant's Gulls book - not the same, as black edges are longer and lacking on P10, but suggestive).
I would very much appreciate any comments about the identity of this bird - thank you.

01: standing bird: 4 images (3 leftside; one right side)
02: flying bird: underwing
03: flying bird: upperwing
04: enlargements of head
05: standing bird: comparison of mantle tone to RBGU and FRGU