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.
The largest of the mergansers, the Common Merganser breeds near lakes and riversides both in wooded flatlands (especially boreal forest) and in mountainous areas of the West. Audubon's climate model projects the species will lose 72 percent of its current summer range. Some summer range expansion is also projected, but much of that is where there is now Arctic tundra, though, so unless large trees grow and die there very quickly, the mergansers will be unable to utilize this new area for breeding. There is a noticeable northward shift of the winter range in the east, that may be habitable if climate change keeps water open further north in the future.