As I understand the issue, the problems surrounding megarhnycha/
fulva/schistacea turn in part on an interpretive anomaly....
are you BSC or PSC?

Megarhycha and schistacea are not closest siblings based on
mitochondrial halotypes [see Zink in Evolution 48(1):96-111].
However, these are the two "subspecies" which show the highest
degree of hybridization. This puts Fox Sparrow taxonomy into a
"Northern Oriole" complex bind and we probably won't see a
split of the other Fox Sparrows until this gets sorted out.

Most megarhyncha at the north end of their range are generally
placed in the "fulva" group which does not have quite as "mega"
a "rhyncha". These have been found to at least the central
Oregon Cascades (Odell Butte, Deschutes Co. in Zink's study, birds
have been captures that are morphologically similar to fulva at
least to Linn Co. OR and observed birds to the OR/WA divide).
Birds in the north Cascades are generally considered schistacea,
though the southern limit is in dispute. It should be noted,
that very few genetic samples were collected from the North
Cascades (at least up to 1994).

I leave you with this from Zink:
"Hybridization between _megarhyncha_ and _schistacea_ involves
apparent non-sister taxa. A "species" consisting of megarhyncha
plus schistacea is paraphyletic...Treating megarhyncha and
and schistacea as conspecific, but iliaca and unalaschensis
as separate species , would misrepresent the recovered pattern
of evolutionary history."

Greg Gillson's effort to collect current information is
available at: http://thebirdguide.com/fox/fox.htm

--
Mike Patterson
Astoria, OR
celata at pacifier.com

Go, and sin no more (ethics in birding)
http://www.surfbirds.com/blogs/mbalame/archives/002555.html