In response to Al Jaramillo's comments about loral color in White-crowned
Sparrows, the black-lored leucophrys and white-lored gambelii intergrade at
Churchill, Manitoba, but I'm not sure how this is manifested. There is a
nice series from Churchill in the Slater Museum including both loral-color
types, and some day I'll look at them in more detail.
Here is clearly a species that would repay molecular analysis, as
has been done in Fox Sparrows (which consist of >1 species certainly). One
of the most interesting findings of molecular analysis of bird populations
is that genetic populations quite often don't agree with morphological
populations (i.e., subspecies). Birds that look alike can have quite
different genes, and birds that look quite different (for example,
Black-capped Chickadees from west and east of the Cascades) can be (as far
as we have been able to measure) genetically identical.
There's a lot more work to be done.

Dennis Paulson
University of Puget Sound
Tacoma, WA 98416