Update: January 08, 2008: added two revealing flight shots from two weeks earlier, at the bottom:
This small (female?) Herring Gull-type gull was at Elliot Landfill,
Corpus Christi, Texas on March 18, 2005; the undertail coverts
are of the "Old World" type and the rest of the plumage
seems consistent with Vega Gull: