The darker the color, the more favorable the climate conditions are for survival. The outlined areas represent approximate current range for each season. More on reading these maps.
This gull is a conundrum. It is difficult to identify, prone to vagrancy and hybridization, and maybe not even a full species. Currently the Thayer’s Gull winters mainly along the West Coast, but with small numbers eastward to the Great Plains and even the western Great Lakes. Audubon's climate model projects a 55 percent loss of current winter range by 2080, with potential for a substantial range shift. In particular, the upper Midwest may soon host considerably more Thayer’s Gulls in winter than is currently the case. The model does not look at climate during the summer on the high-latitude breeding grounds—relatively modest in extent and likely to be affected by climate change.