Reading the crow posts, I began to wonder whether these crow populations
may have been affected by Pleistocene glaciation episodes in the Pacific
Northwest and found some interesting sites and papers for nerds like me.
http://tinyurl.com/ycm63yd

Bird Biogeography (fun stuff on Juncos in here):
http://tinyurl.com/yb4bqgl
"Pleistocene glacial cycles are thought to have played a major role in
the diversification of temperate and boreal species of North American
birds. Given that coalescence times between sister taxa typically range
from 0.1 to 2.0 Myr, it has been assumed that diversification occurred
as populations were isolated in refugia over long periods of time,
probably spanning one to several full glacial cycles. In contrast, the
rapid postglacial range expansions and recolonization of northern
latitudes following glacial maxima have received less attention as
potential promoters of speciation."

Angela Percival
Olympia, WA
Angela at stillwatersci dot com