Has anybody looked at the Carroll Park Nashville Warbler to determine whether 
it is the nominate eastern ruficapilla or the western ridgwayi?   The major 
clue for ridgwayi is constant tail pumping, like a Palm Warbler.   Eastern 
birds can pump their tails occasionally, or even continuously if they are 
agitated, such as a migrant that has just dropped in after a long flight.   Plumage 
differences are subtle but include reduced contrast between head and back and 
increased contrast between back and rump, which is a bright yellow-green in 
ridgwayi.   The yellow of the undersides is brighter and a more pure yellow than 
in ruficapilla and there is a bit more white in the vent area.   All these 
characters are a matter of degree, but are discernible in the field if you get a 
good, long look.

At such a late date, a western vagrant may be as likely as an eastern 
holdover.

Paul O'Brien
Rockville, Mont. Co., MD