Tuesday, August 7, 2018

Warbler Guy, why does American Redstart occur in California more often than most other so-called "East Coast" warblers? Is American Redstart a vagrant on the West Coast?

Excellent question, Joey (in Santa Monica).

Fact is, American Redstart is not always a vagrant in California when detected during the spring and late summer/fall.

That's because its far western home range into Alaska places it in the pathway of where some individuals may migrate up and down the West Coast.

Equally important, a northern California breeding population in the farthest region of the state has occurred in the past.

As a result, it's plausible to suggest annual breeders in this area could be southward migrating individuals that California birders detect from August through November annually, for example, in the outer point of Point Reyes National Seashore in Marin County or at Bodega Head in Sonoma County.

That written, it's ALSO possible some Midwestern and East Coast American Redstarts are seen in California. The species is abundant and locally common throughout much of its range, so, given the plethora of newborns each year, it's possible some become disoriented as vagrants spotted on the West Coast.

In summary, it's challenging to decisively determine the origin of an American Redstart observed from central to southern California. An observer would need to employ bird banding data and recapture a previously banded individual to find out its pathway of dispersion and/or migration.

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