Editor's Note 01/06: Recent genetic studies have shown that Motacilla flava encompasses two or more species, with the N. American race now given full species status (M. tschutschensis) by the AOU Checklist Committee (45th Supplement). Future revisions of this account will reflect these changes.
During the breeding season, the Yellow Wagtail is one of the most conspicuous passerines of the arctic tundra. Its bright yellow coloring, its wagging tail with flashing white outer feathers, its use of elevated perches for observation, pursuit-feeding, singing, and territorial defense, and its loud, sharp, persistent vocalizations when disturbed—all combine to attract the attention of nearly every traveler to northern and western Alaska.
The North American breeding form of this wagtail (M. f. tschutschensis) apparently differentiated in the area of the Bering Land Bridge during the Wisconsin glaciation, at which time the emergent land mass supported a tundra-steppe vegetation. Today, this Beringian subspecies breeds on both sides of the Bering Strait, the continental land connection having been broken some 10,000 years ago by rising sea levels at the end of the Pleistocene glaciations.
In North America, this wagtail's breeding range is restricted to Alaska and to the Beaufort Sea coast of Canada east to the Mackenzie River delta. The Yellow Wagtail is common in much of its range in mainland western Alaska and in the western portions of northern Alaska, but it decreases in abundance farther east. Concentrations of migrants on St. Lawrence Island and on the Seward Peninsula indicate the retention of ancestral migration routes that developed before the most recent submergence of the Bering Land Bridge.
Another Asian subspecies of Yellow Wagtail, M. f. simillima, is a regular spring-passage migrant in the western Aleutian Islands. Widely distributed and well-studied western Palearctic subspecies of the Yellow Wagtail are especially known for their association with large grazing mammals on wintering grounds, for the formation of huge communal roosts on migration, and for their considerable accumulation of fat during the fall premigratory period.