The results of the AOS meeting are in: Thayer’s Gull is now considered a subspecies of Iceland Gull, rather than its own species. There are other changes too, such as a new species of Red Crossbill. For eBird users, these changes will be reflected in August, when eBird taxonomy is fully updated. For everyone, we’ve just lost ourselves a lifer; for hopeless minutiaephiles such as myself, the challenge to ID a “Thayer’s” Iceland Gull has just become even more of a siren call.
The updated AOU checklist: http://checklist.aou.org/taxa/
On the taxonomic history of Thayer’s Gull: http://www.ofo.ca/site/page/view/articles.thayer
On another note, Yellow-rumped Warblers were not split. Audubon’s, Myrtle, etc., all remain a subspecies of Yellow-rumped Warbler, and Blue-winged and Golden-winged Warblers were not lumped!