I photographed this large Larus on 17 Jan 2009 in Puerto Barrios (Department of Izabal, Guatemala). This Caribbean coastal location is the shore of the Bay of Amatique, Gulf of Honduras. The gull most resembles a 1st-cycle Herring Gull (rare but annual at this location), but doesn't seem quite right. Most notably the bill color is advanced for early 1st-cycle, and the rump is quite pale for a 1st-cycle "smithsonianus" Herring Gull. Some possible explanations could be:
1. advanced 7-month old 1st cycle "smith"
2. retarded 17-month-old 2nd-cycle "smith"
3. A 13-month-old "smith" on Southern Hemisphere molt cycle, freshly molted
4. A 6-month-old 1st-cycle F2 hybrid of "smith" and "Nelson's" (Herring x Glaucous)Gull
5. A 6-month old F1 hybrid "smith" x Great Black-backed Gull
6. Something else entirely (ideas?)